CHAPTER VII.

New Process for the Manufacture of Beer.

The principles established in the course of this work implicitly involve the conditions of a new process of manufacture, the essential feature of which would consist in the production of a beer of excellent keeping qualities, we might even say a beer that could not undergo alteration. It will not be difficult now to make ourselves clear on the point.

We have shown in the first place, that the changes which take place in the ferment, the wort, and the beer itself, are due to the presence of microscopic organisms of an entirely different character to that of the ferment-cells properly so called, which organisms, by simultaneously giving rise, in the course of their multiplication in the wort, ferment, or beer, to other products, make the materials difficult to keep or effect their deterioration. Again, we have seen that these change-producing organisms, the ferments of disease, never arise spontaneously in the wort or beer, but, whenever they make their appearance in these fluids, have been imported from without, either in company with the yeast, or from accession of atmospheric dust, or from contact with the vessels, or from the materials themselves which the brewer uses in his manufacture. Moreover, we know that these disease-ferments, or their germs, are destroyed when the wort has its temperature raised to the boiling-point. And, following up the inferences from such facts, we have seen that wort exposed to pure air, after having been heated to boiling, remains absolutely free of any sort of fermentation.

Inasmuch then as the disease-germs of wort and beer are destroyed in the copper in which the wort is boiled, and as, by employing a perfectly pure ferment, we guard against the admission of any foreign ferment of an evil character, we have it in our power to prepare a beer which shall be incapable of undergoing any pernicious fermentation whatsoever. This we shall have effected provided we can take the wort as run off from the coppers, cool and manipulate it out of contact with ordinary air or in contact with pure air, charge it with a pure yeast, and, lastly, store the beer when the fermentation is complete in vessels thoroughly purified from disease-ferments.[162]

§ I.—Preliminary Experiments.

We may readily satisfy ourselves as to the truth of these inferences. The following is one of the earliest experiments which I devised with a view to establish their certainty. Into a flask with a straight neck of about a litre (1-3/4 pints) capacity, a quantity of wort from a brewery was introduced and there raised to boiling, and whilst the vapour still issued from the neck of the flask, connection was made with a two-necked flask in which the cultivation of pure yeast had been carried on. The cork and glass tube used for this purpose had previously been treated with boiling water.

When the wort had cooled down in the flask and matters were arranged as represented in Fig. 75, I raised the two-necked flask so as to cause a little of the liquid and yeast to flow into the wort. Thereupon fermentation was set up, and the resulting carbonic acid gas made its escape by the drawn-out end of the doubled-necked flask. The entire arrangement with its supporting stand remained in this connection for eighteen months, sometimes on a stove, sometimes in the laboratory, exposed to all the variations of external temperature. At the end of that time I tasted the beer in the flask; it was perfectly sound, and the ferment, submitted to the microscope, showed not the slightest trace of any foreign ferments: and, doubtless, the experiment might have been protracted over any number of years with the same result.

The only change that occurs in course of time is the appearance in the neck of the flask at the surface of the beer of a deposit of small prominences resembling a crystallization, but which really consists of those forms of ferment to which in Chapter V. I attached the name of _aërobian ferment_. The beer, after being transferred to a bottle that had been washed with hot water, was kept for several months in the heat of summer, without exhibiting the slightest trace of deterioration.

The essential conditions of the preceding experiment can readily be realized on the large scale. For this purpose we may employ the apparatus in the above sketch (Figs. 76 and 77) constructed of tin or tinned copper. As appears from the sketch, this consists of a cylindrical tub resting on a support, and closed at the top by a cover, whose lower edge fits into a gutter containing water. The wort prepared in the copper is led into the cylinder, a process which does not materially lower its temperature. Now we know that wort in breweries which has been cooled in contact with the air, and so got charged with disease-germs, will, nevertheless, recover its faculty of keeping for any length of time in pure air, if we again raise its temperature to 80° C. (176° F.) or even 70° or 75° C. (158°, 167° F.) Having filled the tub with the hot wort and put on the lid, we then connect, by means of a caoutchouc tube _c d_, the metal tube _a c_ (which opens into one of the tubulures projecting above the lid) with the system of tubes _d e_, _f g_, of which _d e_ is fixed to the cylinder; _e f_ is a caoutchouc junction connecting _e_ with the bent glass tube _g_. We then dash over the apparatus, lid, tubulures, and their corks a quantity of boiling water. This collects in the gutter in which the lid rests, and any excess overflows into a second gutter outside the first, where, however, it cannot remain, but passes away by means of a ring of small holes between the base of the outer trough _i i_ and the cylinder. The overflow is collected in a third trough at the bottom, whence it can be removed by a pipe M. T is a bent thermometer to indicate the temperature of the wort; its bulb is protected by an inlet socket _d d_, pierced with holes; _r_ is a stopcock for discharging the water in the gutter, which serves as a hydraulic junction between the cylinder and its lid; R, V, are stopcocks, or openings for the discharge of the liquid in the cylinder and its deposit. The next process is to cool the vessel, which may be done either by leaving it to itself, or by introducing a current of cold water through the tubulure E, soldered on to the lid. This tubulure is of the form of an inverted funnel, and is pierced at the bottom with a close row of holes, through which the cold water issues in a sheet over the surface of the cover. In whichever way the cooling is effected, the external air continues all the time to enter the vessel beneath the lid by way of the long, narrow passage _g f e d c a_, and must necessarily get purified by depositing in its course all fungoid-germs, just as happened in the case of the two-necked flask of air experiments. This, however, may be still further secured by introducing a small plug of cotton wool, or asbestos, into the end of the tube _g_.

The experiments which we have carried out with this apparatus have proved that, by adopting such an arrangement, beer, a liquid peculiarly liable to change, may be kept as long as we wish, for weeks or months, in contact with air, since the tube _g_ is open, without evincing the least symptom of disease. It matters little whether the leaves and strobiles of the hops are introduced with the hot wort or strained off; the result is the same. On the other hand, a leak in the apparatus from which the wort gets mixed with ordinary water from outside during cooling, will speedily effect a change in the wort and cause it to swarm with vibrios, or butyric ferment, lactic ferment, and other germs of disease, whilst its taste will be rendered extremely nauseous. It can only be through one’s own fault, that is, from want of skill in carrying out the operation, that any change can be brought about by the water in the gutter not being kept out of the fermenting vessel. That water may even become putrid without the organisms contained in it being able to reach the wort in the fermenting vessel. The apparatus may be of any size whatever; we have worked with vessels containing 12 hectolitres with as much ease and certainty as when we used an apparatus of 1 hectolitre (22 gallons).

It is easy to carry out the process of cooling in the presence of carbonic acid gas if we fit a bent tube, similar to _a c d e f g_, to the second tubulure D. Through this tube, or its companion, the gas can be passed as it issues from an apparatus in which it is generated, or from a gasometer filled with it, or from a vessel of beer undergoing fermentation.

However, there is no necessity that the cooling should take place in the fermenting vessel. It may be effected separately, in vessels of greater or less depth, in spiral coils surrounded with cold water, or in any kind of refrigerator, provided always that the conditions of purity are satisfied, and that the flow of the cooled wort takes place under the same conditions. Jets of steam, which are already extensively used for the cleansing of pipes in breweries, may be employed here with great advantage.

The pitching may be effected in various ways. A two-necked flask of a capacity of from 200 to 300 cc. (about 7 to 10 fl. ozs.), in which not more than 100 cc. (3-½ fl. ozs.) of wort has been fermented, will be sufficient for an apparatus of 1 hectolitre (22 gallons), although the flask may not contain more than 1 or 2 decigrammes (1-½ to 3 grains) of yeast. In the manufacture of beer, as at present conducted, the employment of so minute a quantity of yeast would lead to most disastrous results. The fermentation would unfailingly become lactic and butyric, since the foreign germs with which commercial worts and yeasts are always contaminated would have ample time to develop during the first twenty-four or forty-eight hours, whilst the small quantity of yeast used in the pitching could scarcely do more than begin to develop during that time. It is simply with the object of avoiding these secondary fermentations that the brewer uses large quantities of yeast for pitching.

After the wort and yeast have been _pulled up_,[163] a process which every practical brewer adopts after pitching, every part of the liquid is occupied by a multitude of yeast-cells, which seize upon the oxygen in solution, germinate with activity, turn to their own account the food-supplies most easily assimilated, and prevent the growth of the germs of disease-ferments. In the new process which we are now explaining, things happen quite differently. Our wort is pure, and our yeast is pure, and if only a single cell of yeast were introduced into the wort, the vital activity of this would be sufficient to bring about alcoholic fermentation, and to transform the wort into beer, without our having the least reason to apprehend the simultaneous development of any other organisms whatsoever. In short, the new process enables us to pitch with as small a quantity of yeast as we like. It is, nevertheless, inexpedient to employ too minute a quantity, since by doing so we should retard the commencement of fermentation.

In the case of an apparatus of 5 hectolitres (110 gallons) or double that capacity, the pitching may be accomplished by means of flasks holding from 4 to 9 litres (from 7 to 10 or 11 pints), (Fig. 79), or copper cans, tinned inside, holding from 10 to 15 litres (2-1/4 to 3-1/4 gallons), and provided at the upper conical end with glass tubes (Fig. 78). The vessel must be half or two-thirds filled with wort. For this purpose it will be well always to employ wort that has been preserved in bottles by Appert’s process. We must use a stopper provided with tubes, as represented in Fig. 79: _a b_ is a glass stopper which closes the india-rubber tube _b c_; _m n p_ is a fine glass tube, or, better still, made of copper.

The tap R being closed, a long india-rubber tube is attached to the extremity of the curved tube, and the flask is completely immersed in a hot-water bath; the india-rubber tube projects from the bath and keeps the interior of the vessel in communication with the external atmosphere. If the tube _m n p_ is of copper, we may avail ourselves of its flexibility and bend it upwards, so as to place its open extremity outside the bath. The water in the bath is then gradually raised to a temperature of 100° C. (212° F.), at which it is kept for a quarter or half an hour. In the case of copper cans, it is more convenient to place them over a gas-heater. They may be treated in the same manner as the flasks with curved necks. Vessels prepared in this manner may remain in a laboratory, or in any part of a brewery, for an indefinite time, without the wort in them undergoing the least change. It gradually darkens in colour through a direct oxidation of a purely chemical nature, but no tendency to disease will manifest itself.

Some days before we require to pitch an apparatus of several hectolitres, we impregnate one of these flasks or cans.[164] For this purpose we pass the flame of a spirit lamp over the tubes _c b a_ and _m n p_, to destroy the particles of dust that might pass inside at the moment when the stopper _a b_ is taken out, and then by means of a long, straight glass tube we take some of the liquid from a flask or vessel containing pure beer in a state of fermentation, and let a few drops of this, with the yeast that it holds in suspension, fall into the flask or can; the stopper _a b_ is once more passed through the flame and then replaced; generally in the course of one or two days the yeast develops in the flask sufficiently for the fermentation to show itself. We may shorten the operation still further by emptying into the can the contents of one of those double-necked flasks. To do this, we have simply to attach the straight tube of the flask to the india-rubber _b c_, and pour the liquid in. In a similar manner we introduce, through one of the tubulures surmounting the lid of the fermenting apparatus, the contents of the flasks or cans, either whilst they are still in active fermentation, or after fermentation is over. For this purpose, the tap R is connected by means of an india-rubber tube (Fig. 79), with a tube passing through a cork fixed in one of the tubulures of the large apparatus. All this may be done in considerably less time than we have taken to describe it; and the operation may be performed accurately and safely by any one who has witnessed it a few times, even though he may not be skilled in chemical manipulations, especially if he takes care to bear in mind the very simple principles which we have explained.

Since certain parts of the apparatus—the outer opening of the tap, or the india-rubber tubing, for example—may contract particles of dust from the air, those parts, before being used, must be boiled in water, or washed with boiling water, or passed through the flame of a spirit lamp, to destroy the germs mixed with the particles of dust that settle upon them.

The method of cooling the wort in contact with carbonic acid prevents access of oxygen to the latter up to the time of pitching, so that the development of the yeast takes place apart from the influence of oxygen. Now, we know that these conditions necessitate the employment of a very young yeast—a yeast that is in course of active germination, such as may be taken from an incipient preparatory fermentation. Nevertheless, even with this, the development of the yeast under such conditions is extremely slow, and the fermentation takes from fifteen to twenty-five days; whilst, under the same circumstances, but with an aerated wort, it would be finished in from eight to twelve days. This is a considerable drawback, but, perhaps, a still more serious inconvenience is that the beer takes much longer to clarify, and does so with greater difficulty than those beers which are made with aerated worts. At the same time, this is largely compensated by the superior quality of the beer, which is stronger and has greater fulness on the palate, whilst the aroma of the hops is preserved to an extent never found in beers brewed by the ordinary process. Besides this, the yeast deposited at the bottom of the fermenting vessel is much less active, and, being of an older type, is revived with greater difficulty than that which forms in aerated worts. This, which might be considered a disadvantage, if we had to employ the yeast afterwards for pitching, has the great advantage of giving a beer which, when racked, undergoes its secondary fermentation only slowly, and with difficulty.[165] A beer of this kind is better adapted than ordinary beer to stand a long journey without developing great pressure inside the casks, and, if bottled, it will contain very little deposit, and will not froth violently when uncorked. The reason is, that a yeast is the more active, the more ready to multiply rapidly, and to work vigorously the more highly aerated the wort was in which it was grown. On the other hand, a yeast formed apart from air readily gets exhausted, and may even perish in the liquid in which it ferments, when that is kept out of contact with air; in other words, the vital action of yeast is more restricted when it has not been subjected to the action of oxygen during its formation.

If a great depth of wort, the surface of which alone is in contact with atmospheric air, is left to cool down, it will act in almost exactly the same manner as that which is cooled under an atmosphere of carbonic acid gas, because the oxygen of the air is very slow in pervading wort that is undisturbed. The gas will be taken into solution by the upper layer only, whilst the bulk of the liquid will remain unaffected by it. In some experiments which we conducted in a vessel which contained wort to a depth of 70 centimetres (27·5 inches), and which was provided with a tap that enabled us to draw off some of the liquid every day, until we had reduced the depth to 35 centimetres, we found, at the end of eight days, that there was not a trace of oxygen in solution at the latter depth. It is even probable that, considering the slow diffusion of the oxygen, on the one hand, and the combination that may take place between it and certain components of the malt, on the other hand, it would take a long time for all the wort, if undisturbed and of a certain depth, to become saturated with oxygen. In the vessel represented in Figs. 76 and 77 there is a considerable depth of wort to cool down. Nevertheless, the mere fact of the possibility of an aeration from the surface, whilst the wort is cooling down in contact with pure air, is enough to account for a certain effect that is produced on the yeast, later on, for the more youthful appearance of the yeast of the deposit, compared with that which we find in the case of wort cooled in the presence of carbonic acid gas. The difference between the results is particularly striking if, in both cases, we follow up microscopically the development of the yeast during the first few days succeeding the pitching.

The influence of the air on fermentation is considerable. In the ordinary process of brewing, fermentations would be almost impossible, and in every case most defective, if the wort, before being run into the fermenting vessels, were not aerated by its passage over the “coolers,” where the aeration is more or less effective, according as the liquid is more or less shallow. Worts and yeasts being impure, that is containing the germs of foreign ferments, those germs would have time to germinate in the fermenting vessels during the delay that the want of aeration in the wort would cause in the development of the yeast. We are aware that several inventions have been proposed to do away with the coolers, and we feel convinced that the object has been to remedy irregularities in fermentation. Considering the facts which we have published[166] on the development of yeast in the presence of air, and its inactivity in non-aerated media, such inventions ought to be supplemented by some means of further aeration for the prevention of the mischief that they must otherwise cause. In the existing process of brewing, the employment of coolers is a necessity.

The influence of the air on the vital action of the yeast may be proved in ways innumerable. The following is an experiment which we have often carried out with surprising results. A fermentation is going on; we draw off the liquid as rapidly as we please, and pour it back again into the vessel immediately. Within an hour we find a marked increase in the fermentation, evidenced by the liberation of a greater quantity of carbonic acid gas. This experiment may be performed with especial ease if we use the fermenting apparatus that we have described, for, by fitting a gas measurer to the escape tube _a b c d e f g_, the number of litres produced before the drawing off of the liquid may be compared with those obtained after. The least physical change in the running of the fermenting liquid whilst it is being drawn off, modifies the effect in question; such as change in the diameter of the stream, the height from which it falls, its greater or less scattering in falling, all influence it. Again, as might be expected from such results, corresponding modifications take place in the cells of yeast which come under the influence of the air. They become firmer in aspect and outline, their plasma becomes fuller, assumes a younger and more transparent aspect, and the vacuoles disappear. The molecular granulations, too, are less apparent. At a certain focus they disappear; at another they reappear, not as black spots, however, but as brilliant points so small as to be scarcely perceptible. If germination has been suspended it is resumed; in short, everything tends to prove—and having the yeast actually under our eyes we cannot doubt the fact—that the life of the cells is more decided, and the work of nutrition more active after they have been brought into contact with the oxygen of the air, and have absorbed a greater or less quantity of that gas.

Under the ordinary conditions of brewing, the atmospheric air is present in very varying quantities, whether introduced by the wort which holds more or less in solution, or by diffusion over the surface of the vessels, so that the same cells of yeast live by turns without air and with air. At first they absorb all the oxygen held in solution, and multiply under the influence of this absorption. Afterwards, when the supply has been exhausted, and various assimilations have resulted from it, they are deprived of it. Their life continues apart from oxygen, and if the vessel were closed, fermentation would be accomplished under these conditions, although more slowly. The vessel being open, a small quantity of air diffuses continuously through the layer of carbonic acid gas on the surface, and supports the vitality of the cells.

It is interesting to observe that, in the working of breweries, there are several empirical practices the explanation of which is to be found wholly in the fact that the aeration of wort or beer exercises a great influence on fermentation. In many breweries we have seen the pitching performed in the following manner: the brewer, having mixed his yeast in many times its volume of wort, pours all the thick liquid from a height from one bucket into another, and from that back again into the first, and so on a great many times, until the two buckets are filled with the froth enclosing air. In certain London breweries we have seen a bucket suspended by a pulley over the fermenting tun, which is 3 or 4 metres (10 or 12 feet) in depth; this the brewer, by means of a cord, can lower into the tun and pull up again at will, giving it a kind of see-saw movement which agitates the surface of the liquid and aerates it. The use of the fermenting tun itself and the racking of the wort from that tun into casks have the effect of aerating the beer and the yeast, and imparting to the latter a greater vigour and activity.

The resumption of fermentation in cask, after the beer has been run out of the tuns in “low” fermentation breweries is, in our opinion, principally due to the aeration of the beer at the moment when it is racked. The brewer ought to bear in mind that, during racking, every detail is of importance; it makes a great difference whether when the beer is run into the casks it falls from a height or is conducted by a tube to the bottom of the casks, whether it passes directly into the casks, or is poured into them from buckets, and whether it runs in a stream of small or large diameter, since these different methods cause the introduction of corresponding different quantities of air into the beer.

We have devised a simple arrangement for bringing the fermenting liquid into contact with various proportions of atmospheric air. Appended is a sketch of this apparatus (Fig. 80). Instead of one tube serving alike for the entrance and escape of gas, there are two similar ones, each of which opens into one of the tubulures on the cover. Round the other end of one of the tubes is fitted a kind of muff or bag, composed of a cylindrical cage of metallic gauze, over which a layer of well-combed cotton wool is placed, the whole being covered with a muslin bag. The object of this arrangement is to act as an air-filter for retaining the particles of dust. When fermentation has commenced in the apparatus, we have simply to press momentarily the india-rubber connection between the tube from the lid and the tube with the bag. This will at once cause a regular stream of carbonic acid to issue from the end of the uncovered tube, whilst the air will enter by the filtering tube to take its place; and this arrangement will be maintained throughout the whole course of the fermentation, even if we omit the precaution of increasing the power of the syphon by making the tube for the escape of this gas longer than the other one.[167]

It will be readily understood how, whether by this last method, or by the diameter of the tubes, we may vary the conditions of this circulation of air in the apparatus, on the surface of the beer.

§ II.—Method of Estimating the Oxygen held in Solution in Wort.

The use of carbonic acid gas and the cooling of the wort, in contact with that gas or in contact with very limited quantities of pure air, are by no means necessary to the application of the new process. There is only one thing that is absolutely essential—which is, the _purity_ of the gases in the presence of which the wort is cooled and treated. If, therefore, it is well to aerate our wort, either before or during fermentation, this may be done, on the sole condition that the air employed does not introduce any germs of disease that are likely to develop in the beer during fermentation or afterwards. The question of aerating the wort is not, however, so simple a matter as it seems at first sight. A very simple observation will show that wort cannot be safely oxygenated by exposure, without precaution, to the air, even leaving out of account the germs of disease which that air may contain. It is easy to show that finished wort has a decided flavour and aroma of hops, as well as a sweet taste, and that it leaves a certain pleasant, bitter after-taste on the palate. When we taste it in this condition we cannot help thinking that a liquor of the kind, after fermentation, ought to constitute a very valuable beverage, as wholesome as it is pleasant. Now all this pleasant and refreshing sensation that the wort leaves on the palate, which is due as much to the aroma as to the bitterness of the hop, disappears absolutely, we may say, if the wort is left exposed to contact with air for a sufficient time, and that whether the air be warm or cold. We may easily perform the experiment in one of our two-necked flasks, in which we can preserve the wort, in contact with pure air, without any fear of change. The oxygen of the air enters into combination with the substances that the hop introduces into the wort, and the wort, in consequence of this oxidation, gradually becomes transformed into a saccharine decoction, without odour, in which even the bitter flavour is destroyed or hidden. In other words, the wort grows weak and flat, in just the same way that beer and wine do, as well as all the various natural or artificial worts which serve to produce them. Thus it is evident that considerable care is necessary in subjecting wort and beer, whether in course of manufacture or finished, to the action of atmospheric air. If, therefore, it is a good thing to supply wort with oxygen, as we have already pointed out, in order to facilitate the fermentation and nourish the yeast, it is, on the other hand, important that the quantity supplied to it should not be too great, otherwise we may injure the quality of the beer, and particularly its fulness on the palate, that is its apparent strength, which has very little to do with the proportion of alcohol in it. The strength of a beer is intimately connected with those substances introduced by the hops into the wort and thus into the beer, to which we previously alluded, and of which too little is known; their properties and the palatableness resulting from them are very readily affected by the oxygen of the air.[168]

We have, therefore, to ascertain the measure in which air occurs during the process of brewing, and whether, in the actual process, there may not be too great a proportion of active oxygen present. The study of this subject requires that we should know what quantities of oxygen may be held in solution in the wort or absorbed by direct combination. Fortunately this has been rendered a comparatively easy matter by a rapid method of estimating the oxygen held in solution in liquids of various kinds, devised by M. Schützenberger in 1872. As soon as this method was made known, we requested M. Raulin, who was attached to our laboratory as assistant-director, to apply it to the determination of oxygen in wort. This he did with his accustomed skill, devising certain alterations of details which rendered the method at the same time surer and more expeditious.

The principal feature in M. Schützenberger’s process consists in the employment of a salt, the properties of which that chemist was the first to recognize; he has named it _hydrosulphite of soda_, and it is obtained by the action of zinc filings on a solution of bisulphite of soda, out of contact with air.

Hydrosulphite of soda S^2O^2,NaO,HO, which is isomeric with hyposulphite of soda, only differs from the bisulphite by two equivalents of oxygen.[169] When brought into contact with free oxygen, it absorbs that gas instantaneously and becomes converted into bisulphite; similarly when mixed with water, it immediately absorbs the oxygen held in solution. Again there are colouring matters, such as M. Coupier’s soluble aniline blue, that are instantaneously decolourized by hydrosulphite of soda, whilst they resist the action of the bisulphite. If, taking care to avoid the access of air, we add hydrosulphite of soda to a certain volume of water—a litre, for example—that has been deprived of air and faintly coloured with Coupier’s blue, we shall see that a few drops will be sufficient to effect the decoloration. If, on the contrary, the water is aerated, the decoloration will not be effected before a sufficient quantity of the hydrosulphite has been added to absorb the oxygen in solution, and the volume of the reagent required is in proportion to the quantity of oxygen in solution in the water. To render the process sensitive, we must dilute the hydrosulphite to such an extent that 10 c.c., for example, may correspond very nearly with 1 c.c. of oxygen. If the reagent would keep we should only have to determine directly, once for all, the volume of oxygen that a known volume of the liquid could absorb; but, in consequence of its extreme liability to change through contact with air, it is necessary to titrate the liquid every time before using it. This is easily done in the following manner:—

According to the observations of Messrs. Schützenberger and Lalande, the hydrosulphite decolourizes an ammoniacal solution of sulphate of copper, reducing the copper to a lower state of oxidation; the sulphite and bisulphite having no action as long as there is an excess of ammonia. We prepare a strongly ammoniacal solution of sulphate of copper, containing such a quantity of copper that 10 c.c. of the liquid will correspond, as far as action on the hydrosulphite is concerned, with 1 c.c. of oxygen. Calculation by equivalents gives us the correct value verified by direct experiment.[170]

The object of the modification which M. Raulin has introduced, is to avoid the loss of time thus occasioned by the changes which take place in the titrated liquids by long keeping, as well as certain errors which may arise from the acidity of the wort. On this latter point M. Schützenberger has remarked that the quantities of hydrosulphite of soda corresponding with one and the same volume of oxygen vary with the acidity of the liquid operated upon, a phenomenon which that skilful chemist explains by the formation of oxygenated water, of varying stability in media of different acidity.

Instead of determining the strength of the titrated solution of hydrosulphite before each operation, we take the solution as it happens to be, and determine its strength by causing it to act on a known volume of pure water saturated with oxygen at a certain temperature. The tables of solubility of oxygen in water give the exact volume of oxygen on which the measured volume of hydrosulphite used has acted. According to Bunsen, about one minute’s brisk shaking in a closed bottle, with excess of air, will be sufficient to effect the maximum saturation of the water at the temperature at which we operate.

For experiments on wort we require:—

1. A 2-litre (3-½ pints) flask, A, containing _saturated_ hydrosulphite of soda,[171] of such strength that 2·5 c.c. will be sufficient to absorb almost all the oxygen in 50 c.c. of water saturated with air at the ordinary temperature (that is, 1 volume of hyposulphite must equal 20 volumes of water).

2. A 2-litre flask, B, containing a solution of indigo-carmine, 50 c.c. of which will be decolourized by about 20 c.c. of the hydrosulphite. This solution contains about 20 grammes (30·7 grains) of commercial indigo-carmine per litre (1·76 pints).

3. An apparatus, C, for the production of hydrogen.

4. An experimental apparatus composed of a burette, D, graduated in tenths of a cubic centimetre, and a three-necked Wollf’s bottle, E.

5. A flask, F, holding about 100 c.c. provided with a straight tube divided into tenths of a cubic centimetre, and containing a solution of ammonia of such strength that about ten drops of it will neutralize the acidity in 50 c.c. (1·76 fl. oz.) of wort.

To perform the operation we shake about 150 c.c. (5·3 fl. oz.) of distilled water, at the existing temperature, in a 1-litre flask for a minute or so; this saturates it with air, and we must at the same time note the temperature. To be extremely precise, we should note also the barometrical pressure.

Into the bottle E we introduce about 50 c.c. of the indigo solution, and 200 c.c. of water at about 60° C. (140° F.), and fill the tube _e_ to the point _b_ with water saturated with air; we then expel the air from the bottle E by a current of hydrogen. The blue colour of the liquid in the bottle is then very carefully brought to a yellow tint, by running in, drop by drop, the hydrosulphite with which the burette D is filled.

We next pour 50 c.c. of distilled water saturated with air into the funnel _a_, and pass it into the flask; the blue colour reappears. We must then bring back the colour to exactly the same tint of yellow. Let _n_ represent the number of divisions on the burette denoting the volume of hydrosulphite employed for this purpose.

We repeat this last operation immediately, taking 50 c.c. of the wort, the oxygen of which we wish to determine, having first introduced into the funnel _a_ a sufficient number of drops of the ammoniacal solution to neutralize the acidity of the wort. Let _n´_ represent the number of divisions of hydrosulphite employed to restore the yellow tint in the case of the wort.

We once more perform the experiment with 50 c.c. of saturated water; let _n´´_ be the number found.[172]

The ratio which the quantity of oxygen held in solution in the wort bears to the quantity of oxygen contained in the same volume of water saturated with air, at the temperature _t_, and under the pressure H, will be

it will be sufficient in most cases to bear in mind this ratio.

When we want to deduce the absolute quantity of oxygen held in solution in a volume V of the wort, we have merely to multiply this ratio by the quantity of oxygen contained in the same volume of water saturated with air, at the temperature _t_ and under the pressure H, a very simple problem if we know the coefficients of the solubility of oxygen in water at different temperatures. These coefficients are given for ordinary temperatures in the following table, which was compiled by Bunsen. We have restricted the numbers to three places of decimals:—

Temperatures. Coefficients. 0° C. (32° F.) 0·040 1° C. (33·8° F.) 0·040 2° C. (35·6° F.) 0·039 3° C. (37·4° F.) 0·038 4° C. (39·2° F.) 0·037 5° C. (41·0° F.) 0 036 6° C. (42·8° F.) 0·035 7° C. (44·6° F.) 0·035 8° C. (46·4° F.) 0·034 9° C. (48·2° F.) 0·033 10° C. (50·0° F.) 0·033 11° C. (51·8° F.) 0·032 12° C. (53·6° F.) 0 031 13° C. (55 4° F.) 0·031 14° C. (57·2° F.) 0·030 15° C. (59·0° F.) 0·030 16° C. (60·8° F.) 0·029 17° C. (62·4° F.) 0·029 18° C. (64·4° F.) 0·029 19° C. (66·2° F.) 0·028 20° C. (68·0° F.) 0·028

The primary condition which enables us to rely on the exactness of this method is the fact which we have mentioned above, that a liquid if shaken up with air for one minute will become perfectly saturated with oxygen. Substantially this is the case. In estimating the oxygen in different parts of a liquid treated thus, we have invariably obtained the same figures to within about 1/50th.

It is true that the variable quantity of the oxygen held in solution in the liquid contained in the part of the tube _eb_, as well as the oxygen absorbed during the treatment of the liquid in contact with air, constitute causes of error. Experience, however, proves that these causes of error are insignificant, as long as we have to deal with a liquid the aeration of which is not very far removed from the point of saturation, and whose solubility-coefficient for oxygen is not widely different from that of water for the same gas. Under such conditions we have always found a constant ratio, to within about 1/40th between the same liquid and air-saturated distilled water, placed under the same circumstances.

If, on the other hand, we have to deal with a liquid which holds but a minute quantity of oxygen in solution, the causes of error mentioned may very seriously affect our results, and it will be absolutely necessary to avoid them. The liquid experimented on must be treated out of contact with air, by aspirating it directly from the vessel that contains it into the pipette H, which is graduated for 50 c.c., and causing it to pass thence into the flask E, by substituting the pipette for the funnel _a_. Finally, before arranging the pipette, we cause a small quantity of the liquid in the flask, which has been previously brought to the exact yellow tint, to pass, by pressure, through the tube _eb_, so as to avoid the cause of error that is likely to result from the air held in solution in the liquid of that tube.

The liquid, the oxygen of which has to be determined, may also be passed directly from the vessel containing it into the flask E; the rest of the operation being performed as already described.

It was by this method that the oxygen held in saturate solution in wort was determined. The following are the principal results obtained by M. Raulin:—

1. At different pressures the ratio between the quantities of oxygen held in solution in water and in wort is, all other conditions being similar, constant. This ratio has been found equal to 1·20 in the case of wort and water saturated with air at the ordinary pressure, and 1·24 in the case of wort and water saturated with pure oxygen.

2. The ratio between the coefficient of the solubility of oxygen in water and that of its solubility in wort is very nearly constant at different temperatures, increasing, however, slightly as the temperature diminishes.

This ratio has been found to be—

Temperatures. 26° C. (78·8° F.) 1·20 19·5° C. (67·1° F.) 1·25 4° C. (39·2° F.) 1·37

Another wort gave the following results:—

Temperatures. 9° C. (48·2° F.) 1·15 21° C. (69·8° F.) 1·10 25° C. (77·0° F.) 1·07

3. The ratio between the quantities of oxygen held in solution in water and those held in solution in wort increases with the concentration of the wort. By evaporating the same wort to different degrees of concentration, and afterwards saturating it with air, at the same temperature, we obtained the following figures for the ratio in question:—

Weak wort 1·06 The same evaporated to half 1·15 “ ” “ 2/5 1·27 ” “ ” 3/10 1·45 “ ” “ 1/6 1·96

4. Worts of different origin, but of the same density and temperature, when saturated with oxygen, always contain very nearly the same quantity of that gas.

Two portions of the same wort, shaken up with air, one being hot the other cold, then left to themselves for some time, and afterwards saturated with air, at the same temperature, gave the figures 1·22 for the ratio between the oxygen in the water and that in the wort.

Different worts of the same density, saturated at a temperature of 15° C. (59° F.), gave the following ratios:—

Wort kept in a bottle with air for 19 1·140 months

Wort recently prepared 1·142

Wort kept in a bottle without air for 20 1·142 months, aerated for 18 days

Wort evaporated to dryness and made up 1·126 with water

5. The solubility of oxygen in wort differs very little from the solubility of oxygen in sweetened water of the same density.

An experiment was made with a solution of sugar on the one hand, and with wort more or less diluted with water on the other hand, at the same temperature of 11° C. (51·8° F.). The following figures were obtained for the ratios of solubility:—

Solution Wort. of Sugar.

Marking 17·9° 1·278 1·27 Balling[173]

“ 14·0° ” 1·190 1·15

“ 7·0° ” 1·092 1·06

6. From the preceding results it is easy to deduce a general formula which shall give the coefficient of solubility of oxygen in any wort, marking B° by _Balling_, and at temperature _t_°.

From the figures of (2) it follows that above and below the temperature of 15° C. (59° F.), the ratio which the coefficient of solubility of oxygen in water bears to that of the solubility of the same gas in wort varies about 0·006 for each degree of the thermometer. From the figures of (3) it follows that the same ratio varies about 0·002 for each degree of _Balling_ above and below the 15th degree on the instrument.

By taking _c_ for the coefficient of solubility of oxygen in water at _t_° C., and _c´_ for that of oxygen in wort also at _t_° C., and having a density B, by _Balling_ at 15° C.; and taking X for the ratio _c_/_c´_, at 15° C. and 15° _Balling_, we shall have

_c_/_c´_ = X + (B - 15) 0·022 - (_t_ - 15) 0·006.

By carefully ascertaining the ratio _c_/_c´_ for different worts, and adopting the preceding formula, we have found for X a mean value of 1·16.

The definitive formula, therefore, is:

(1) _c_/_c´_ = 1·16 + (B-15) 0·022 - (_t_ - 15) 0·006,

or again,

(2) _c_/_c´_ = 0·86 - (B - 15) 0·016 + (_t_ - 15) 0·004.

The coefficient _c_ of the solubility of oxygen in water will be found in the table given a few pages back.

§ III.—On the Quantity of Oxygen existing in a state of Solution in Brewers’ Worts.[174]

The wort, when it comes from the copper in which it is boiled with the hops, remains exposed upon the coolers for a time, the length of which varies according to circumstances, the most important of which is the exterior temperature. The average time is from seven to eight hours, during which the volume of the wort diminishes, whilst its density increases; at the same time, it deposits its proteinaceous matters and absorbs oxygen from the air, either by way of solution or of combination.

In the present paragraph we shall confine ourselves to the uncombined oxygen held in a state of solution in wort, recognizable by the change of colour produced by its action on white indigo.

The use of the coolers enables the brewer to obtain his wort in two distinct states of limpidity—filtered wort and unfiltered wort. At the same time there is a further difference between these worts, namely, in the quantity of oxygen held in solution. The unfiltered wort comes direct from the coolers; the wort to be filtered, mixed with a part of the deposit, is run into a special vessel, from which it is distributed over the filtering surfaces, which are generally of felt; filtered bright, it is then received in a reservoir, from which it is distributed amongst special fermenting vessels. Falling through the air in a thin stream of drops, it must necessarily have become charged with a greater quantity of oxygen than ordinary wort. In good breweries it is put apart by itself to ferment, and the yeast which it yields is firmer and deposits more easily than that of unfiltered wort. As for the fermentation, it is, under similar conditions, quicker by a day or a day and a half than in the case of ordinary wort. The difference in the quantity of oxygen held in solution in the two kinds of wort is greater in proportion as the external temperature is lower; in winter it may be twice as great as in summer. The reason is that in summer a boiling wort does not obtain a minimum temperature of 20° C. (68° F.), on the best coolers, in less than six or seven hours. After leaving the coolers it is passed over a refrigerator. In winter it attains that temperature in about three hours, or less, which then goes on sinking on the coolers. During the last two or three hours which are employed in bringing the temperature still lower, as also during the running off, the wort absorbs an appreciable quantity of oxygen. In other words, wort in winter remains for a longer time at low temperatures, in free contact with air.

Another circumstance unites with this exposure upon the coolers to increase the aeration of the wort; the wort is run into the fermenting tuns through pipes of large sectional area, more or less bent, and carries with it by suction considerable quantities of air, which, from the continual agitation, gets well mixed with it. The effect of this mixing in the pipes is to considerably increase the proportion of air in solution in the wort, especially in winter, when the temperature of the wort is lower; and from the figures given below we may, although it is very variable, put the average increase at a quarter of the whole amount. The calculation has been made by comparing the quantities of air held in solution in two samples of the same wort, one of which was taken from the coolers at the moment of “turning out,”[175] and the other from the fermenting vessel after it was filled.

Let us call the ratio between the quantity of oxygen held in solution by a wort, and that which the same wort would hold in solution if saturated at the same temperature, the _degree of saturation_ of that wort at the temperature _t_.

The determination of degrees of saturation is reduced to a comparison of the number of divisions of hydrosulphite _n_ which satisfies the wort in the first case, with the number _n´_ corresponding with the same wort saturated at the same temperature. The ratio _n_/_n´_ gives the degree of saturation at the temperature _t_.

In experiments made with a wort at 14·5° _Balling_ as mean density, we found the following results:—

In summer, in the case of worts reduced to the temperature of 5° C. (41° F.) by a refrigerator, the degrees of saturation may be set down as—

For unfiltered worts 0·500 For filtered worts 0·800

In winter, in the case of some worts which were racked at a temperature of from 3° to 4° C. (37·4° to 39·2° F.), without the use of a refrigerator, we found the saturation complete in both worts. In the case of a very low external temperature, however (-10° C., 14° F.), we have failed to determine the saturation in an unfiltered wort. As regards the mean winter figures, in the case of worts racked at a temperature of 5° C. (41° F.), they may be fixed at these:—

For unfiltered wort 0·850 For filtered wort 0·950

In autumn and spring we find the mean figures to be intermediate between those given above:—

For unfiltered wort 0·500 to 0·850 For filtered wort 0·800 to 0·950

From these ratios it is easy to find the quantity of oxygen contained in brewers’ worts, if we also refer to Bunsen’s Tables and the formula (2) given in the preceding section. At the temperature of 5° C. (41° F.), at which the above worts were “gathered,”[176] and not taking into account the very small correction that should be made for the difference of half a degree on Balling, we find, by this formula, as the ratio of the coefficients of the solubility of oxygen in saturated wort and in water—

_c´_/_c_ = 0·82

Now, at the temperature of 5° C., the quantity of oxygen held in solution in 1 litre of water is, according to Bunsen, 0·036 litre, at the atmospheric pressure, and therefore at the pressure of 1/5th atmosphere, which is that of the oxygen in atmospheric air, it will be—

0·036/5 litre = 7·2 c.c.—[that is, 2 cubic inches per gallon.]

And, consequently, in the case of saturated wort, it will be—

7·2 c.c. × 0·82 = 5·904 c.c.—[that is, 1·62 cub. inches per gall.]

Multiplying this last number of c.c. by the different _degrees of saturation_ found, we shall obtain the volumes of oxygen held in solution in 1 litre of different worts:—

Summer worts {Unfiltered 0·500 × 5·904 c.c. = 2·952 c.c. {Filtered 0·800 × 5·904 “ = 4·723 ”

Winter worts {Unfiltered 0·850 × 5·904 “ = 5·018 ” {Filtered 0·950 × 5·904 “ = 5·609 ”

It is important to notice that we are here dealing with wort taken from the fermenting vessel just before it was pitched; that is to say, when the quantity of oxygen held in solution was as large as the treatment to which it had been subjected allowed of its being. The mode of taking it for examination is as follows:—A burette, H (Fig. 81), is plunged into the fermenting vessel, the temperature of which at the time is ascertained very exactly, the upper part of the burette being fitted with an india-rubber tube, _a b_, longer than itself. The liquid is then sucked up the tube, and soon completely fills the apparatus and runs out at _b_ (Fig. 82). By lowering the tube the whole arrangement thus forms a syphon, and enables us to let the wort that we are experimenting on flow for some minutes; when every trace of air has been thus expelled, the lower tap is closed and the liquid is introduced into Schützenberger’s apparatus.

As for the saturated wort, the value of which in oxygen serves to determine one of the elements of the degree of saturation, it is readily obtained by introducing a volume of from 100 c.c. to 150 c.c. of wort into a 2-litre or 3-litre flask, and shaking it briskly so as to saturate it with air; it is then poured into a settling-glass, to separate it from the great quantity of froth formed in the shaking, and then, by means of a graduated pipette, 50 c.c. is taken for examination.

We have spoken of the influence that oxygen has on the activity of yeast, on its development and, consequently, on the progress of fermentation. Moreover, we know, from experiments already mentioned, which we communicated to the Academy and the Chemical Society in 1861, that the rapid development of yeast in contact with air is in reciprocal relation to the disappearance of the oxygen from the air. Knowing the conditions of the aeration of wort from the moment when it arrives on the coolers until the moment when, in the fermenting tun, it is about to be pitched, it would be interesting to ascertain what happens to the oxygen dissolved in the wort at the moment of pitching, how yeast is affected when suddenly brought into contact with that oxygen; what part, in short, that gas plays in fermentation.

Let us therefore follow up, hour by hour, the degree of saturation after pitching, in Tourtel’s brewery. On November 4th, 1875, some wort at 14° Balling was pumped on to the coolers at 7 p.m., and at 4 a.m. went down to a 32-hectolitre (700 gallons) tun, its temperature then being 6° C. (42·8° F.) The pitching, in which about 100 grammes (3·2 oz. troy) of pressed yeast was used per hectolitre (22 gallons), took place at 5 a.m. The following is the curve of the degrees of saturation of the oxygen, as drawn by Messrs. Calmettes and Grenet.

The abscissæ represent the time expressed in hours, and the ordinates give the degrees of saturation of the wort with oxygen. It will be seen that about twelve hours after the pitching, and at a temperature of 6° C., all the oxygen had disappeared, absorbed by the yeast. We shall find that wort by itself, unassociated with yeast, would also have combined with oxygen; but in the course of twelve hours, at 6° C., this combination would have been scarcely appreciable in absence of yeast. It follows, therefore, that the oxygen in solution is taken up by the yeast, under the conditions of which we are speaking. This has been proved directly by an experiment. A double quantity of yeast was employed for a tun similar to the preceding one, and it was found that the oxygen in solution disappeared completely in less than half the time that it took to disappear in the first case.[177] It is very important to notice that in our 32-hectolitre tun, at the moment when we determined the complete disappearance of the oxygen in solution, the cells of yeast had assumed a younger and fuller appearance than they had at first; but they had not multiplied at all up to that time, nor were there even any buds then visible on them. The oxygen, therefore, must be stored up somehow in the cells, taken up by their oxidizable matters to be brought into work subsequently, or to act as a _primum movens_ of life and nutrition, spreading its influence over several successive generations of cells.

§ IV.—On the Combination of Oxygen with Wort.

The atmospheric oxygen is not merely taken into solution by wort; it also combines with it, as a very simple experiment will suffice to show. If we place in a tinned iron vessel some boiling wort, separated from the hops in the copper, and cool it suddenly by plunging it into iced water, and after having cooled it down in this manner to 15° or 20° C. (59° or 68° F.), saturate it with oxygen, by shaking it briskly in a large flask, and then completely fill a vessel with it and close it up for twelve hours, we shall find at the end of that time, if we test it with the hydrosulphite of soda, as we have described in § II., that it does not contain a trace of free oxygen. The whole of the gas which was originally held in solution will have entered into combination, that is to say, the liquid, first coloured blue with the indigo-carmine, and then brought to a yellow tint by means of the hydrosulphite of soda, will not regain its original blue colour through the action of this wort. The following experiments were undertaken with the object of studying this property of wort, and in order that we might form some idea of its importance, and of the total quantity of oxygen that wort can absorb under certain special circumstances. The experiments were performed in our own laboratory on wort from Tourtel’s brewery, which M. Calmettes had forwarded to us in bottles prepared in the brewery at Tantonville, in the following manner: Each bottle was filled with boiling wort taken from the copper and closed with a bored cork, through which the neck of a funnel passed; the funnel also was filled with the wort, and the whole preserved from contact with air by a layer of oil. The next day the bottles were corked full by the help of a bottling needle,[178] previously heated, with perfect corks that had been passed through the flame. The bottles arrived in Paris in very good condition, quite full of the liquid up to the corks. They were left undisturbed for one or two days at the same temperature as that to which they had been exposed during the corking and the journey. The object of this was to afford time for a deposit of the wort to form at the bottom of each bottle. As a matter of fact, we know that wort boiling in the copper is charged with proteinaceous matters and other floating and insoluble substances. The wort above the deposit was turbid and opaline; it was in this state when we used it for our experiments. It may be taken for granted, without risk of appreciable error, that the wort had been absolutely deprived of oxygen in solution, inasmuch as it had been bottled when boiling, and had cooled down out of contact with air. As for the quantity of oxygen that it might have held in combination, this must have been insignificant, although there must have been some, since the wort had been exposed to the air in the copper; the oxygen in combination, however, could have had no appreciable influence on the results which we obtained. Let us call this wort _boiled wort_.

_First Experiment._—Into a straight-necked flask we introduced a certain measured quantity of this wort by means of a syphon, taking care that the syphon should only act on the opaque wort, and should not reach the deposit at the bottom of the bottle. We then drew out the neck to a fine tube in the flame and boiled the wort; and during ebullition we sealed the end of the fine tube. After it had cooled, we arranged that pure air should enter the flask. To do this we made a file mark near the fine closed point of the flask, and connected the point by a piece of india-rubber tubing with a glass tube containing a column of asbestos, which we heated. We then broke off the point of the flask inside the india-rubber tube, so that the air entered the flask after being filtered through the asbestos. We removed the india-rubber tube and sealed up once more the fine end of the neck at the point where we had broken it off. Finally, to aerate the wort to saturation, we shook the flask briskly for some minutes, and then placed it in a hot-water bath, where we left it for about a quarter of an hour. We afterwards removed it to an oven at 25° (77° F.). We repeated the same operation next day and the four succeeding days.

The wort, which at first was scarcely coloured, gradually assumed a reddish-brown tint, and deposited an amorphous matter, but without brightening. It became clear, however, when filtered, which was not the case with the turbid, opaline wort in the bottles when they arrived.

The following is an analysis of the air in the flask, made immediately after a renewed and vigorous shaking, the object of which was to saturate the wort with air before analyzing the supernatant air:—

November 29th.

Temperature at which the flask was refilled with air 4° C. (29·2° F.)

Atmospheric pressure 751 mm. (29·6 ins.)

Total volume of flask 333 c.c. (20·32 cub. in.)

Volume occupied by the wort 120 “ ( 7·32 ” )

December 8th.

Volume of gas analyzed 27·6 c.c. (1·68 cub. ins.)

After treatment with potash 27·4 c.c. (1·67 “ )

” “ pyrogallol 22·4 ” (1·36 “ )

Oxygen 5·0 c.c. (0·305 cub. in.)

Composition of the gas:— Per cent.

Oxygen 18·25

Nitrogen 81·57

The formula which we deduced above (§ II.) allows us to conclude that at the temperature of 8° C. (46·4° F.), which was the temperature at which the wort was saturated before the analysis given above, the quantity of oxygen in solution in the 120 c.c. (4·2 fl. oz.) of wort was 0·84 c.c. (0·051 cub. in.).

At the moment when the flask was closed, the total volume of oxygen, calculated to zero and 760 mm. (30 in.) pressure, was 44·73 c.c. (2·729 cub. in.).

At the moment when the analysis was finished, the volume of oxygen was calculated to the same conditions of temperature and pressure, 38·86 c.c. (2·355 cub. in.); 5·87 c.c. (0·374 cub. in.) has, therefore, disappeared. Now, as there is 0·84 c.c. (0·051 cub. in.) in solution, there has, consequently, been an absorption, by combination with 120 c.c. of wort, of 5·03 c.c. (0·32 cub. in.) of oxygen, or 41·7 c.c. per litre (11·6 cub. ins. per gallon).

_Second Experiment._—In a similar experiment, in which, however, the flask was kept for five days at a rigorously constant temperature of 55° C. (131° F.), day and night, and in which the supernatant air was not shaken up with the wort, we found—

Volume of gas analyzed 28·5

After treatment with potash 28·3

“ ” “ pyrogallol 23·0

Oxygen 5·3

Composition of the gas:— Per cent.

Oxygen 18·6

Nitrogen 81·4

Total oxygen at first 29·40

“ ” remaining 26·04

“ ” that has disappeared 3·36

“ ” in solution 0·54

“ ” in combination 2·82

Or per litre, 35·2 c.c. (9·8 cub. ins. per gallon).

The colour of the wort in this experiment had become sensibly similar to that of the wort in the preceding experiment.

_Third Experiment._—In another experiment we left the flask, for the same length of time again, after it had been refilled with air and reclosed, at a temperature which varied between 2° and 4°C. (35·6° and 39·2° F.). In this case we found—

Volume of air analyzed 27·8

After the action of potash 27·8

After pyrogallic acid 22·3

Oxygen 5·5

Composition of the gas:— Per cent.

Oxygen 19·7

Nitrogen 80·3

Total oxygen at first 29·40 c.c.

“ ” remaining 27·58

“ ” that has disappeared 1·82

“ ” in solution 0·44

“ ” in combination 1·38

Or per litre, 17·20 c.c. (4·8 cub. ins. per gallon).

In this last experiment the wort was scarcely darker in colour. Its colour, compared with that of wort cooled on the coolers in the brewery, was slightly darker; but the difference, although it existed, was scarcely appreciable. We shall revert to this fact, which is of importance, presently.

_Fourth Experiment._—The following series of experiments were undertaken to enable us to form some idea of the rapidity with which oxygen is absorbed by wort.

We employed three flasks. A, B, C, of the following capacities:—

A = 234

B = 214

C = 203

into which we introduced the following quantities of wort (boiled wort, without air):—

Into A 96 c.c.

“ B 84 ”

“ C 84 ”

The necks of the flasks were then drawn out and sealed in a flame, the liquid being at a temperature of 5° C. (41° F.). The flasks were then placed in a hot-water bath and kept at 100° C. (212° F.) for a quarter of an hour. The flask A was repeatedly shaken during cooling, as also was the flask B, this being omitted in the case of the flask C.

The contents of flask A were submitted to analysis as soon as it was quite cooled—that is to say, in about three hours. The analysis of contents of B and C was delayed for about twenty-four hours. We took the precaution of not commencing the analysis before we had shaken the flasks for a few minutes, so that the wort in all of them might be saturated at a fixed temperature, and thus enable us to ascertain the exact quantity of oxygen in solution.

The analyses showed that the worts in the three flasks contained:—

Flask A, oxygen in combination, per litre 20 c.c.

“ B, ” “ ” 21·4 c.c.

“ C, ” “ ” 16·8 c.c.

Several facts may be deduced from these experiments: the shaking up of the wort with air has a marked effect on the absorption; a very appreciable absorption immediately follows the shaking up of the wort when warm; whereas, in the case of cold wort that has remained undisturbed, the absorption takes place slowly.

The results of the preceding experiments plainly show that the wort, which is very hot when it comes on to the coolers, where it remains for several hours, must absorb an appreciable quantity of oxygen by combination; but these same experiments teach us nothing definite concerning the volume of oxygen that is actually absorbed. We can only gather from the remark which concludes the third experiment given above, that the total quantity of oxygen absorbed by the wort in Tourtel’s brewery, during the time that it remains on the coolers, must be less than 17 c.c. per litre (4·7 cubic inches per gallon), inasmuch as the coloration effected by combined oxygen in the proportion of 17 c.c. per litre was considerably greater than that of the wort taken from the backs in the brewery.

If we knew the curve of cooling on the Tourtonville coolers we might easily, in experiments conducted in our laboratory, assimilate the conditions of our experiments to those of the oxidation of the wort in the brewery, by exposing wort in contact with air in closed flasks to temperatures varying according to the indications of the curve in question. For this purpose, we induced M. Calmettes to study the process of cooling upon the coolers at Tantonville. In Fig. 84 the figures found in one of that gentleman’s experiments are given.

The abscissæ represent the time expressed in hours; the ordinates, the degrees of temperature. The exterior temperature was 0° C. (32° F.); the atmosphere was calm. The wort was pumped on to the coolers at 5.20 p.m., its temperature then being 85° C. (185° F.), and the operation of pumping lasted from 5.20 to 5.30 p.m. The first determination was made at 5.30 p.m., and was repeated every ten minutes until 7.30 p.m. Between 7.30 and 8.30 p.m. it was repeated every twenty minutes; after that, it was repeated every half-hour until 2 a.m., when the wort went down to the fermenting vessels. The mean depth of the wort was 8·5 centimetres (3·1 inches).

Having determined the rate of cooling in the brewery, we made the following experiment: a known quantity of wort from the copper—deprived, consequently, of oxygen—in the same condition as when it comes on the coolers, was put into a graduated, cylindrical vessel, which was then closed with an india-rubber cork, and placed immediately, without being shaken, in a hot water bath at 85° C. (185° F.). Another vessel similar to the preceding one, and having a thermometer passed through the cork, and immersed in the wort, enabled us to observe the temperature. The temperature was gradually reduced, in exact accordance with the data of the preceding curve, until the water, in the course of eight hours and a half, was brought down to 10° C. (50° F.). It is true, that we cannot pretend to have realized all the conditions of the coolers, in this manner, but we approached them very nearly; moreover, it was an approximation rather than a rigorous determination that we desired to obtain. We then collected over mercury the air which remained in the flask, and analyzed it very carefully; at the same time, with Schützenberger’s apparatus, we determined the oxygen held in solution in the wort so treated. From the results thus obtained we easily found the quantity of oxygen that had disappeared—that is, the oxygen which the wort had acquired from the atmosphere of the flask, and which had combined with the oxidizable matters of the wort.

The volume of the flask being 815 c.c., that of the wort 391 c.c., and the depth of the liquid 8 cm., we found an absorption by combination of 9·49 c.c. of oxygen per litre of wort (2·63 cub. ins. per gallon). Another flask treated in the same manner gave us similar results.

As the oxygen in solution has so great an influence on fermentation, it is important that we should, likewise, know the effect produced by the oxygen in combination. The following considerations and experiments may throw some light on this subject:—

We have already remarked that natural saccharine worts oxidize, and acquire colour in contact with air, and that this coloration disappears when these worts are caused to ferment. This furnishes one presumption, that the oxygen in combination disappears then, from, being abstracted by the ferment. A similar phenomenon is observable in the case of wort. After having acquired a marked dark shade by remaining in contact with pure air, it loses this colour very appreciably during fermentation; and if the wort does not quite regain the colour which it originally had when it came from the copper, this circumstance is probably owing to the fact that the quantity of oxygen in combination with the wort is larger than that which is abstracted by the yeast. We have seen that yeast absorbs oxygen, since, in the case of a saccharine wort, more or less saturated with oxygen in solution, when fermentation commences, the first effect of the ferment is to cause that oxygen to combine with its own substance. We should, therefore, expect to find the oxygen in combination, as well as that held in solution, in wort, abstracted by the yeast and contributing to the activity of fermentation. As a matter of fact, this is proved by direct experiments, for the fermentation of a wort that has oxidized in contact with air, or of one from which all the oxygen that was held in solution in it has disappeared by direct combination, is much more easy, rapid, and complete than the fermentation of the same wort when it contains no oxygen, whether free or combined. These experiments were as follows: we boiled some _copper wort_ in a large double-necked flask, like those shown in Fig. 73; all the air being expelled, pure air was allowed to enter the flask; and when the wort was cool it was saturated with this air, by being shaken briskly for a quarter of an hour. The wort was then forced by a pressure of air, applied to the extremity of the S-shaped tube, into smaller flasks, similar to the preceding ones; these we filled completely, and then plunged the end of their sinuous tubes under mercury. After waiting for two or three days, a longer time than was required for the oxygen in solution to enter into combination—a fact which we confirmed by means of a similar flask, which served as a standard—we caused the wort, so prepared, to ferment in the flasks, and side by side, for the sake of comparison, some _copper wort_ that contained no air in solution or combination.

In other experiments we operated on pure wort, saturated with oxygen in combination, by being allowed to remain for one year in an open flask in contact with pure air. This wort was deprived of air in solution by a protracted boiling over mercury. It was then pitched, out of contact of air, with an old yeast. The yeast underwent no development at all, a proof that oxygen in combination cannot act like oxygen that is free, or simply in solution, in effecting the revival of the yeast; nevertheless, after the revival has been once started by means of a small quantity of air, fermentation declares itself with much greater facility than in the case of copper wort, placed under the same conditions, but deprived of oxygen in combination.

§ V. On the Influence of Oxygen in Combination on the Clarification of Wort.

Oxygen in combination has another effect which it is essentially important to point out, for it concerns the clarification of beer. One of the most valued properties of this beverage is its limpidity and brilliancy. We know from the results of the fourth experiment in the preceding paragraph that in the case of a wort shaken up when hot with air, and examined as soon as cold, that is, after an interval of only three hours, we find a notable volume of oxygen to have been absorbed by combination; in the experiment to which we allude, this volume was not less than 20 c.c. of oxygen per litre of wort. The shaking up of the wort when cold with air saturated it with oxygen in solution, but the quantity of oxygen which under these conditions entered into combination, in the course of three hours, is insignificant, although saturation by solution may be attained in the course of one minute’s shaking. If two samples of the same wort are shaken up with air, one of them being hot and the other cold, and both filtered after having been left undisturbed for twenty-four hours, or even immediately after the agitation, we cannot fail to be struck with the great difference that they will present in point of brightness. The wort that was shaken up hot will have more colour, and will be brilliant; the other will be turbid, and will not become clear for five or six days, when left to itself in contact with air and filtered again. This explains a fact that may be easily verified in practice: Boiled wort, if cooled down suddenly, or slowly but out of contact with air, or shaken up cold in contact with air, is opaque when filtered; whilst the same wort, cooled down on the coolers where it has taken a certain quantity of oxygen into combination, generally passes through the filter very bright. The intelligent brewer is uneasy when this is not the case, for it cannot be denied that the easy clarification of wort has a favourable influence on the easy clarification of beer.

It would, nevertheless, be a grave error to suppose that the clarification of beer must necessarily follow that of wort, and we may be permitted to make a digression here on the subject, to prove this statement.

On February 3rd, 1874, we brewed 2 hectolitres (44 gallons) of beer. The boiling wort, hops and all, was run into a vessel like that represented in Fig. 80, but provided in addition with a false bottom, pierced with holes and fixed at 1 centimetre (0·39 inch) above the true bottom of the vessel; this was meant to retain the spent hops. The temperature of the wort in the vessel after it was filled, February 3rd, 4 p.m., was 90° C. (194° F.), that of the room was 10° C. (50° F.). We permitted the wort to cool down gently, without running cold water over the vessel. The wort indicated a density of 14° Balling.

The following temperatures were taken:—

Temp. of Temp. of Wort. Room.

Feb. 4, 11 a.m. 38° C. (100·4° F.) 9° C. (48·2° F.)

7 p.m. 30° C. ( 86° F.) 9° C. (48·2° F.)

11.30 p.m. 26·3° C. ( 79·3° F.) 9° C. (48·2° F.)

Feb. 5, 9 a.m. 21° C. ( 69·8° F.) 8° C. (46·4° F.)

12 a.m. 19·75° C. ( 66·6° F.) 8° C. (46·4° F.)

4 p.m. 18° C. ( 64·4° F.) 8·5° C. (47·3° F.)

Feb. 6, 11 a.m. 14° C. ( 57·2° F.) 8° C. (46·4° F.)

Feb. 7, 2 p.m. 11° C. ( 51·8° F.) 7° C. (44·6° F.)

At the end of this time the wort drawn from the smaller tap half-way up the vessel had already become very bright, although it was taken from the bulk of the liquid above the deposit of hops.

On February 8th the temperature of the wort was 9·5° C. (49·1° F.), and that of the room 5° C. (41° F.); the wort was again very bright. Taken from the small tap and tested by Schützenberger’s process it gave no evidence of free oxygen in solution, although its surface was in contact with air. It continued absolutely pure, the arrangements of our vessel, as we have already explained, allowing only such air to enter as was first deprived of its disturbing germs.

Not till February 12th, after we had again determined the purity and brilliant clearness of the wort, a brilliancy which we can compare with nothing so well as Cognac, without the faintest trace of cloudiness, did we set it to ferment in a vessel similar to that in which it had cooled, but without the false bottom. In the process of transfer we effected its aeration by causing it to fall on a small inverted tinned iron capsule some 4 or 5 centimetres (1-½ to 2 inches) in diameter. By this arrangement the wort took up air to the extent of rather more than a third of its saturate capacity, that is to say, by spreading over the capsule, and falling from it in a kind of sheet, it absorbed a volume of oxygen more than a third of the total amount of oxygen which it was capable of absorbing at the existing temperature; this was 12° C. (53·6° F.) at the moment when the wort was drawn off. The pitching was accomplished with a 6-litre flask containing about 4 litres (7·04 pints) of beer that had been in “low” fermentation from February 3rd. The beer was cleansed on February 24th, and had a density of 5-1/4° Balling. We collected 2·345 kilos (75·39 oz. troy) of yeast, containing 56 per cent., that is, 1·313 kilos (42·21 oz. troy) of pressed yeast, containing 36·7 per cent. of yeast dried at 100° C. (212° F.), that is 482 grammes (15·49 oz. troy) for the brew, which would give 241 grammes (7·748 oz. troy) of yeast formed per hectolitre (22 gallons).

The beer was turbid when drawn off, and the small glassful that we removed did not brighten in twenty-four or even forty-eight hours. The samples for some days previously had been in the same condition. The yeast existed as a fine deposit without any straggling yeast about the sides. The want of brightness was dependent rather on spurious colour than on any actual turbidity. We may here remark that if in the preceding experiment the wort had taken up oxygen into combination as well as into solution at the time that it was aerated, the other conditions being the same, the beer would have been bright and better.

It follows from this experiment that a wort may be _perfectly bright_ at the moment when it is pitched, yet fail to produce a beer which shall be bright when racked, or one that will brighten subsequently otherwise than with great difficulty. We may add that when we repeated this same experiment, cooling the wort, however, as rapidly as the conditions of our apparatus permitted, and employing iced water, the beer appeared very nearly bright when it was racked, and brightened pretty quickly in cask and in bottle. The total duration of cooling was not longer than two hours.

The question here arises what part does the oxygen combined with wort play in the clarification of the latter, or in the clarification of beer? Although it may be difficult to give a definite answer to this question, we must bear in mind that in cases where the beer brightens best, if we examine it under the microscope during fermentation, we see, besides the clusters of yeast-cells, floating amorphous particles, which are larger and more compact than those to which the turbidity of worts and muddy beers is due, a circumstance which should lead us to suppose that the oxygen in combination with the wort has the effect of modifying the nature of the amorphous deposit which is produced during the fermentation of the wort. During boiling, the hop yields to the wort a variety of resinous, odorous, and astringent substances, which, for the most part, are held in solution by the presence of sugar and dextrin. At the moment when, under the influence of the yeast, which is itself more or less oxidized, the sugar becomes transformed into alcohol and carbonic acid, a portion of the bitter and resinous matters of the hop becomes insoluble and remains in a state of suspension in the liquid. It is very probable that at this point it is when the combined oxygen assumes its function of modifying the physical structure of these insoluble particles, agglomerating them, so that they become more easily deposited.[179]

Moreover, oxidation tends to form a special precipitate in the wort, which precipitate contributes towards the collection and deposition of the very fine particles suspended in the wort, by a mechanical action, similar to that which we notice in fining operations. On the coolers an effect of this kind is produced. The wort in the copper contains insoluble matters which pass on to the coolers. Very bright when boiling, it grows turbid as it cools, and then contains two kinds of insoluble substances: 1. Substances insoluble alike in the hot and cold liquid, some of which even, as we have just seen, are formed under the influence of heat and air: all these substances precipitating rapidly to the bottom of the vessels. 2. Very fine particles insoluble in the cold, but soluble in the hot liquid, appearing as the wort cools down, and giving it a milky appearance. If the air does not come into play they remain in suspension for an indefinite time, so to say. Wort taken boiling from the copper and cooled down, therefore, forms a considerable deposit at the bottom of the bottles. Now, if we put this wort into bottles without filling them, putting into some only the milky wort from above the deposit, and into others the same wort along with some of the deposit, then raise it to 100° C. (212° F.), and before it has time to cool down shake it up with air a good many times, it will be readily seen that the wort in the bottles containing the deposit will brighten more rapidly and satisfactorily than those in the bottles without the deposit. The deposits which are insoluble in the copper have, therefore, an influence on the clarification. We must add, however, that this influence cannot be compared with that of direct oxidation.

The “turning out” of the wort and its stay upon the coolers to a certain extent exhibit the different conditions which take part in its clarification, inasmuch as the wort charged with its insoluble matters is run off very hot, and with more or less violence against the external air.

§ VI.—Application of the Principles of the New Process of Brewing with the Use of Limited Quantities of Air.

We have now an idea of the quantities of oxygen which occur, free or combined, in the actual processes of manufacture. We know, moreover, that an excess of air may be injurious, especially to the aroma of the beer, and to that quality which consumers prize so highly, which goes by the name of _bouche_. It must, therefore, be important to ascertain whether in existing processes the proportion of active oxygen may not be excessive.

The best practical means of determining this would consist in comparing the products of different processes with progressively increasing access of air, starting from none at all, as in the case of cooling in the presence of an atmosphere of carbonic acid gas. The following arrangement (Fig. 85) permits us to realize these conditions:—

The wort brought to a temperature between 75° and 80° C. (167° and 176° F.) in the double-bottomed vessel C, passes by the tube _a b_ into a refrigerator, such as Baudelot’s, for example, but acting in an inverse manner to the ordinary mode of using Baudelot’s; that is to say, the wort is made to circulate inside the tubes, whilst the cold water plays on the outside.[180] The wort when cooled, its temperature being indicated by a thermometer _c_, passes down by the tube _c_DD to fill the fermenting vessel A. This vessel is made of tinned iron, or, better still, tinned copper, and has a cover provided with a man-hole and eye-hole; _m n_ one of the tubes for the circulation of air during fermentation; its connecting-tube is not represented, it would be behind the vessel.

At the point _d_ there is a pipe for admission of pure air; this is represented on a larger scale at T. The wort, as it runs through the large tube, carries with it air from outside, and this air is calcined on its way in by means of a flame which plays on the copper tube through which it passes. This arrangement supplies a third or more of the total quantity of oxygen that the wort is capable of acquiring by solution at the temperature at which we work.

F represents the arrangement of the reversed funnel in which the tube _m n_ terminates. Its mouth is closed with cotton-wool held in place between two pieces of wire gauze, for the purpose of purifying the air that enters by it into the fermenting vessel during fermentation.

_v_ is an entrance tap for steam, by means of which the vessel and refrigerator are cleansed from all extraneous germs before each fermentation, and before the wort passes into the refrigerator.

When the fermenting vessel A is at work, we may start a fermentation in a second vessel in the following manner: opening a small tap situated at about a third of the height of the vessel, we pass a few litres of the fermenting beer into a can of tinned copper, previously purified by a current of steam, and filled with pure air. This can is then emptied into the fresh vessel, an operation of no difficulty, since we have merely to connect the tap of the can with the small tap of the vessel, and lastly, the vessel is filled with wort, which then mixes with the fermenting liquid. These various manipulations, it is evident, are performed under conditions of complete purity, without the slightest contact of the liquids either with the exterior air or with utensils contaminated by disturbing germs.[181]

It is seldom that an industry adopts at once in their entirety new practices which would necessitate a re-arrangement of plant, and the process of which we are speaking would require such re-arrangement, as far as the fermenting vessels and the method of cooling the wort are concerned. The new process would, however, be of great value if once introduced, simply for the manufacture of pure ferment and pure wort, or even for that of pure ferment alone. In other words, we might retain the ordinary methods employed in low fermentation, use the same method of cooling or the new one, the same fermenting vessels, and the process of fermentation at low temperatures; the yeast, however, would be prepared in a state of purity in the closed vessel which we have described, collected in those vessels, aerated, and then employed after the old-established custom; better still, the pitching might be performed with beer in the act of undergoing pure fermentation.

Above the fermenting-stage there might be arranged a room for the vessels used in the new process, from which the pure beer could be run for pitching purposes into the large tuns in the brewery below. It is true that beer prepared in this manner would not be perfectly pure, but from the results which have been obtained by working on this system, there is no doubt that it would possess keeping qualities far superior to those of beer made with ordinary yeast, even supposing that beer to have been treated with every possible precaution, and to be as pure as any produced in the best regulated breweries.

In the month of September, 1874, we conducted an experiment at Tantonville, in a closed vessel capable of holding 6 hectolitres (132 gallons). The deposit of yeast served to pitch an open vessel, the wort of which had, moreover, been cooled under conditions of purity. The cooling had been effected by means of the Baudelot refrigerator, represented in Fig. 85, the wort in the closed vessel having been similarly treated. For shortness sake, we may designate the closed vessel and its beer by the letter K, and use the letter M for the open vessel and its beer, and T for the corresponding beer of the brewery. The vessel K was pitched on September 4th, and racked on September 17th, the beer then showing a density of 5·5° Balling.

The beers K and M were sent to Paris at the same time as some barrels of the beer T, brewed by the ordinary process; and samples of these different beers, which arrived on October 22nd, were procured from five different cafés for purposes of examination.

The beer M did not suffer by comparison with the beer T. The similarity between the flavours of these two was so close as to puzzle even experienced judges. In both cases the beer was brilliantly clear. In two cafés the beer M was even preferred to T, being considered softer on the palate (_moelleuse_) and of more decided character (_corsée_) than T, a circumstance which may be explained by the fact that its wort had been less aerated.

The beer K, although very clear and bright, was considered inferior to M, but the sole reason of this was that at the date when it was tasted—November 3rd—it did not froth. As we have already remarked, a peculiarity of the beers made in closed vessels is that their secondary fermentation takes a longer time to develop. The yeast held in suspension in the beer, at the moment when it is drawn off, is, in the case of all beers, the yeast of a supplementary fermentation, if we may use that expression. In the ordinary process of brewing, this yeast, in consequence of the greater aeration of the wort at the commencement of fermentation, is more active, or, rather, more ready to revive and multiply than is that which develops in closed vessels. If the barrels of the K beer had been tapped on the 12th or 15th of November, instead of on the 3rd, it is probable that they would have contained as much carbonic acid gas as the beer M contained at the earlier date. This delay in the resumption of fermentation, which characterizes beer made in closed vessels, is an advantage, inasmuch as it facilitates the transmission of the beer to long distances, besides giving us the smallest deposits of yeast in cask or bottle, as we have already pointed out.

In comparing the keeping qualities of the beer M and the beer T (the latter being the brewery beer), we made the following observations:—[182]

On November 25th we began to detect in the brewery beer an unsound flavour; a large deposit, too, had formed; the beer had lost its brilliancy, and frothed enormously. The deposit swarmed with diseased ferments, especially those represented in Nos. 1 and 7 of Plate I. The beer M, on the contrary, was in brilliant condition, with an insignificant deposit, and an ordinary froth, if anything, rather small, and beautifully bright.

On December 3rd the beer M was still good, very clear, and in excellent preservation; it was considered by professional brewers as remarkably sound.

December 22nd, the same beer M was still very bright and good.

January 20th, the beer was still bright; for the first time, however, we detected in the deposit in the bottles, which was still small, the filaments of turned beer. This unsoundness was in its earliest stage. Now, comparing the relative unsoundness of the two beers, we see that M kept at least two months longer than the corresponding brewery beer. This example shows us that as far as the keeping powers and the quality of beer are concerned, the existing process would gain considerably by the employment of pure wort and pure ferment; and, indeed, it seems likely that the new process may be introduced into breweries with this object in view.

In the course of the summer of 1875 we made the following observations on the keeping qualities of a beer brewed on the new system, all the details of which had been rigorously carried out. The beer brewed at Tantonville during the months of June and July, at a temperature of 13° C. (55·4° F.), in 50-litre and 80-litre casks (11 and 18-gallon), had been sent by slow trains to Arbois (Jura), where we were staying for a time. The temperature of the wine cellars in which these barrels were stored was, on June 1st, 12·5° C. (54·5° F.); this rose gradually until September 1st, when it attained 18° C. (64·4° F.). In this cellar the brewery beer, brewed in the ordinary way, underwent change in the course of fifteen days or three weeks, whilst the beer brewed on the new system remained sound for several months. It is true that some of the barrels lost their frothiness, and that the beer in them underwent a peculiar vinous change, but these effects in no way depend on the conditions peculiar to the new process.

Comparing the beers K, M, T, of which we have been speaking, we see that, however useful the aeration and oxidation of the wort may be in quickening fermentation and facilitating clarification, yet it is by no means indispensable to the success of our operations that we should introduce into our worts large quantities of oxygen, whether by solution or combination. Beyond a certain limit—a limit which is undoubtedly overstepped in the existing process—oxygen is injurious to the palate characteristics and aroma of beer.

These comparisons have proved to us that the new process can be applied to wort aerated to the third of its saturate-capacity for oxygen, and pitched with a good “low” yeast, taken from the fermentation of a wort aerated in the same way, and that the beers thus obtained not only possess vastly superior keeping properties, but are equal in quality and superior in palate-fulness to beers brewed with the same wort on the existing system. We should be perfectly justified in forming this conclusion as to the _strength_[183] of the beer furnished by the new process, even if on tasting it we found that the new beer M was merely equal in strength to Tourtel’s beer brewed in the ordinary manner, since the wort in the new process, other conditions being the same, is weaker than the same wort treated in the usual way, from not having undergone that evaporation on the coolers which concentrates it. If we were to restore to the concentrated wort of ordinary brewing all the water lost by it through evaporation, the beer that we should obtain would be sensibly weakened.[184]

One thing, however, is that we must employ good varieties of “low” yeast. We have seen how the employment of certain forms of yeast renders the clarification of beers difficult, as well as extremely slow, and almost prevents their falling bright at the end of fermentation. These yeasts, moreover, frequently impart to beer a peculiar yeast-bitten flavour, which does not disappear even after a prolonged stay in cask. Even repeated growth of these yeasts, whether in closed or in open vessels, and no matter what quantity of air we may supply them with before fermentation, seems to have no effect in changing their character. The only thing we can do with these varieties of yeast is to get rid of them with all speed, and to replace them with others.

Notwithstanding the comparative success that has attended various trials of the new process on the commercial scale, that process has not yet been practically adopted: and here we must bear in mind that we have not to deal with any casual invention or mechanical improvement that could be introduced all at once into the working of a brewery; we are dealing with operations of considerable delicacy, which necessitate the adoption of a special plant to carry them out. Under such conditions time and labour are required to effect a change in the established processes of a great industry. This, however, cannot diminish the confidence that we have in the future of our process, and it is our hope that the same confidence will be shared in by all those who may give this work an attentive perusal.

Footnote 162:

M. Galland, a brewer in Maxéville, near Nancy, published with his name, in November, 1875, a pamphlet, which was reproduced in the brewing journals of that date, bearing the title, _It is said, “the air being impure, let us exclude it;” I say, “The air being impure, let us purify it.”_ These two aphorisms, together or apart, constitute the essential novelty of my researches on beer, and M. Galland is mistaken in attempting to appropriate the merit of the second alternative (see my note in the _Comptes rendus_ of the 17th November, 1873, and the text of the letters-patent obtained 13th March of that year). M. Galland has devised some arrangements for putting the latter of these two schemes into practice; but it is possible, of course, to effect this in a variety of ways. M. Velten, a brewer in Marseilles, had already accomplished this in his efforts to carry out practically the procedure advocated in the present work.

Footnote 163:

[Non-technically, stirred about.—ED.]

Footnote 164:

As stated in the paragraph on aërobian ferments, in Chapter V., “low” yeasts, to be preserved in their state of “lowness,” must be submitted to often-repeated growths—every fifteen days in winter and every ten days in summer, that is to say, they must be grown afresh after each of these intervals. If this is done, there will be no reason to apprehend the formation of aërobian ferments, which, as we have stated before, may embarrass us by transforming our “low” yeasts into “high” yeasts.

Footnote 165:

It has been observed by brewers that, sometimes, without any apparent cause, a yeast suddenly becomes inactive and fermentation ceases. Accidents of this kind may probably be explained in the same manner as the facts of which we are speaking. If a wort has not been aerated, or if it has been deprived of oxygen by a commencing development of microscopic organisms, the yeast formed in it will be very inferior, and the fermentation may stop at its commencement or soon afterwards. In such a case, an aeration of the yeast and wort would be the best remedy.

Footnote 166:

PASTEUR, _Comptes rendus de l’Académie des Sciences_, vol. lii. p. 1260, and _Études sur le Vin_, 2nd Edition, p. 277.

Footnote 167:

We may here remark that the system of gutters in the above apparatus is much simpler than that described in connection with Figs. 76 and 77. The water which falls on the cover is carried off, when the gutter is full, by a circle of grooves, inclined so that the streams running from them meet and form more readily a sheet of water, which flows over the exterior surface of the cylindrical vessel.

Footnote 168:

[It will be well for the reader to bear in mind, that the word “strength,” used by Pasteur many times in this chapter, has a different meaning to that which attaches to it in the minds of English brewers, who in nearly every case use it in reference to _original gravity_, while the author employs it, in this chapter, at any rate, to denote the _palate characteristic of strength_, in other words _palate-fulness_. For this reason we have thought it best in many cases to actually substitute the term “palate-fulness,” or “body,” for the literal translation of the French word “force.”—F. F.]

Footnote 169:

[As some confusion has existed in the nomenclature of these salts, it may be as well to offer some explanation.

The salt here used for absorbing oxygen was discovered by Schützenberger, and named by him _hydrosulphite of soda_. It no longer now goes by that name, being called _hyposulphite of soda_, NaHSO_{2}.

The salts formerly known as _hyposulphites_ are now called _thiosulphates_, as Na_{2}S_{2}O_{3}.

Thus to put them together we have:—

Hyposulphite (Hydrosulphite) NaHSO_{2} Bisulphite NaHSO_{3} Thiosulphate (Hyposulphite) Na_{2}S_{2}O_{3}

The thiosulphates were formerly regarded as containing the elements of water in their composition, thus:—Na_{2}H_{2}S_{2}O_{4}, which being halved would give NaHSO_{2}, isomeric with hyposulphite, as Pasteur says. It is further to be observed that Pasteur uses the old notation, in which the number of atoms of sulphur and oxygen are the double of what they are in the new.—D. C. R.]

Footnote 170:

SCHÜTZENBERGER, _Comptes rendus de l’Académie des Sciences_, vol. lxxv., p. 880.

Footnote 171:

M. Schützenberger applies the term _saturated_ to a solution of hydrosulphite prepared thus, or very nearly so; a current of sulphurous acid is passed through a solution of commercial bisulphite of soda, to excess; 100 c.c. (3-½ fl. oz.) of this solution and 30 grammes (46 grains) of zinc filings are put into a small flask, so as to completely fill it; the bottle is corked up and the mixture is shaken briskly for about a quarter of an hour. Lastly, the contents of this flask are poured into a large 2-litre flask, with water and containing milk of lime, prepared by mixing 100 grammes (3·2 troy oz.) of quicklime in the water just before it is used. The whole is shaken briskly for some minutes and then left to settle. The supernatant liquid soon becomes bright. This is the hydrosulphite; but in this state it is too concentrated; and should be syphoned into another 2-litre flask half full of water. In the alkaline condition this salt absorbs gaseous oxygen much less rapidly than in the acid, so that the liquids will retain their strength much longer, if they are kept in well-corked bottles.

Footnote 172:

The numbers _n_ and _n´´_ will vary as the wort, or liquid which we have to test, is perfectly neutral or otherwise. Should it be acid _n´´ n_, should it be alkaline _n n´´_. This would be a very exact method of estimating the acidity or alkalinity of any coloured liquid.

Footnote 173:

[The Balling saccharometer being almost unknown in England, we may explain that its indications are for percentages of sugar in saccharine solutions, or of extract in worts; 17·9° Balling, therefore, means 17·9 per cent. of sugar or extract in the respective liquids.—F. F.]

Footnote 174:

Experiments made, at our request, by MM. Calmettes and Grenet, at Tantonville; in Tourtel’s brewery.

Footnote 175:

See foot-note, page 367.

Footnote 176:

[For non-technical readers we may explain the expressions “gathered,” here used, and “turning out,” used on page 365. “Turning out” describes the operation of emptying the _copper_ contents into the _hop-back_, or the _hop-back_ contents on to the _coolers_. “Gathering” refers to the time when the worts are finally intermixed and _weighed_, prior to the commencement of vinous fermentation.—F. F.]

Footnote 177:

We know also from the direct experiments of M. Schützenberger, performed on aerated water with which yeast had been mixed, that yeast causes all the oxygen in solution to disappear very quickly, so that hydrosulphite gives no evidence of a trace. (See SCHÜTZENBERGER, _Revue scientifique_, vol. iii. (2), April, 1874).

Footnote 178:

[The bottling needle (_foret â aiguille_) is a contrivance for permitting a cork to be driven into a bottle completely filled with liquid, without bursting the bottle. It consists of a slightly-tapering iron pin about 1/8th inch in diameter and 2 inches in length, somewhat flattened, and slightly curved throughout its entire length, with a groove running down one side from end to end, the pin being jointed with a ring, like a common ring cork-screw. In using it the pin is driven into the bottle alongside the cork, thus allowing the excess of liquid to escape as the cork advances. When the cork is completely home, the needle is withdrawn, and the elasticity of the cork enables it to fill up the space left, so that we have the bottle corked air-tight, and no air left between the cork and liquid.—D. C. R.]

Footnote 179:

We have remarked in our observations on No. 6 of Plate I. (p. 6) that amongst the amorphous granular deposits of wort and beer we often find minute balls of resinous and colouring matter, perfectly spherical and very dense, which if the liquids be shaken up will render them very turbid, but which readily and rapidly deposit again, without remaining in suspension in the least. Such then is the form in which the deposits of wort in course of fermentation are precipitated, when the wort has been freely exposed to oxygen. One day in the laboratory we were desirous of starting a fermentation in a vessel capable of holding 12 hectolitres (264 gallons). But as we only had at our disposal a copper capable of holding 2-½ hectolitres, we procured the wort from a neighbouring brewery in two barrels of 6 hectolitres each. This wort we re-heated, in portions, in our 2-½ hectolitre copper, a treatment which had the effect of oxidizing the wort more than it would have been in the brewery. In this case the beer fell remarkably bright, and the cells of yeast were accompanied by the deposit of minute agglomerations sketched in Plate I., No. 6. We have repeated this experiment on a smaller scale and have obtained the same result.

Footnote 180:

It is evident that this arrangement may be modified in many ways. Any of the ordinary worms, or, generally speaking, any of the more modern refrigerators invented during the last few years, may be adopted. The only point that is of importance is the preservation of the purity of the wort during cooling.

The Baudelot refrigerator is extensively adopted in France; for this reason we used it in our experiments at Tantonville. We might equally well, by enclosing the worm in a casing of sheet iron or tinned copper, pass our wort over the exterior of the tubes, the cold water passing through them. The wort would cool quicker in this way than with the arrangement described in the text, and if we arrange to admit only pure air into the case, always under conditions of purity. The aeration, moreover, could be made as much as we wished.

Footnote 181:

This arrangement limits the proportion of oxygen that may be introduced into the wort by direct oxidation. But it would be easy to increase this at will, by causing the wort as it comes from the copper and the hop-back to pass into a cylinder turning horizontally on its axis and furnished with blades fixed inside, so as to divide the wort and bring it better into contact with the air in the cylinder. Instead of a revolving cylinder we might use a fixed vessel, in which the wort could be stirred up by some arrangement outside. In either case we should have to take care that the air was pure when it came into contact with the wort, but this would be a matter of no difficulty; we would simply have to make communication with the outer air by means of a tube filled with cotton wool. Any air that might be in the vessel at the moment when the wort was introduced would be purified by the high temperature of the wort coming from the copper. We should, moreover, gain the great advantage of being able to bring oxygen to bear on our wort in determinate amounts. From this vessel it would pass on to the refrigerator. We might again raise the wort oxidized on the coolers to a temperature of 75° C. (167° F.), to recool it in this manner and aerate it by means of the pure-air pipe.

Footnote 182:

One of the barrels of the brewery beer was bottled about the end of October, at the same time that a barrel of M was.

Footnote 183:

Refer foot-note, page 354.

Footnote 184:

The evaporation on the coolers varies according to the arrangements in different breweries; but in no case is it less than several hundredths of the total volume. One special advantage of the new process is that it gives us, _ceteris paribus_, a volume of beer that is 5, 6, or 7 per cent. greater than that which we should obtain by the old process, without in any way affecting the strength of the beer. It is easy to ascertain the quantity that evaporates on the coolers, by determining the quantity of water that must be added to a known volume of wort coming from the coolers to bring its density back exactly to that of the original wort, both being calculated to the same temperature. Bate’s English saccharometer, which shows differences of nearly 1/1000th in density, may be employed with advantage in this determination.

APPENDIX.

Whilst this work was passing through the press there appeared two small works on the subject of the generation of inferior organisms.

One of them was by M. Fremy. The author’s object seems to have been merely to give an account, under a new form, of the part which he took in the discussion on the origin of ferments that was carried on before the Academy of Sciences in 1871-1872. In the course of that discussion M. Fremy had announced his intention of publishing an extensive Memoir, full of facts, bearing on the subject. The perusal of the promised work gave us much disappointment. Not only were our experiments, and the conclusions which we drew from them, given there, for the most part in a manner which we could not possibly accept, but, moreover, M. Fremy had confined himself to deducing, by the help of his favourite hypothesis, a series of _à priori_ opinions based on half-finished experiments, not one of which, in our opinion, had been brought to the state of demonstration. To tell the truth, his work was the romance of hemi-organism, just as M. Pouchet’s work of an earlier date was the romance of heterogenesis. And yet, what could be clearer than the subject under discussion? We maintain, adducing incontestable experimental evidence in support of our theory, that living, organized ferments spring only from similar organisms likewise endowed with life; and that the germs of these ferments exist in a state of suspension in the air, or on the exterior surface of objects. M. Fremy asserts that these ferments are formed by the force of hemi-organism acting on albuminous substances, in contact with air. We may put the matter more precisely by two examples:—

Wine is produced by a ferment, that is to say, by minute, vegetative cells which multiply by budding. According to us, the germs of these cells abound in autumn on the surface of grapes and the woody parts of their bunches; and the proofs which we have given of this fact are as clear as any evidence can be. According to M. Fremy, the cells of ferment are produced by spontaneous generation, that is to say, by the transformation of nitrogenous substances contained in the juice of the grape, as soon as that juice is brought into contact with air.

Again, blood flows from a vein; it putrefies, and in a very short time swarms with bacteria or vibrios. According to us the germs of these bacteria and vibrios have been introduced by particles of dust floating in the air or derived from the surface of objects, possibly the body of the wounded animal, or the vessels employed, or a variety of other objects. M. Fremy, on the other hand, asserts that these bacteria or vibrios are produced spontaneously, because the albumen, and the fibrin of the blood themselves possess a semi-organization, which causes them, when in contact with air, to change spontaneously into these marvellously active minute beings.

Has M. Fremy given any proof of the truth of his theory? By no manner of means; he confines himself to asserting that things are as he says they are. He is constantly speaking of hemi-organism and its effects, but we do not find his affirmations supported by a single experimental proof. There is, nevertheless, a very simple means of testing the truth of the theory of hemi-organism; and on this point M. Fremy and ourselves are quite at one. This means consists in taking a quantity of grape juice, blood, wine, &c., from the very interior of the organs which contain those liquids, with the necessary precautions to avoid contact with the particles of dust in suspension in the air or spread over objects. According to the hypothesis of M. Fremy, these liquids must of necessity ferment in the presence of pure air. According to us, the very opposite of this must be the case. Here, then, is a crucial experiment of the most decisive kind for determining the merits of the rival theories, a criterion, moreover, which M. Fremy perfectly admits. In 1863, and again in 1872, we published the earliest experiments that were made in accordance with this decisive method. The result was as follows:—The grape juice did not ferment in vessels full of air, air deprived of its particles of dust—that is to say, it did not produce any of the ferments of wine; the blood did not putrefy—that is to say, it yielded neither bacteria nor vibrios; urine did not become ammoniacal—that is to say, it did not give rise to any organism; in a word the origin of life manifested itself in no single instance.

In the presence of arguments so irresistible as these, M. Fremy, throughout the 250 pages of his work, continues to repeat that these results, which, he admits, seem subversive of his theory, are, nevertheless, explicable by the circumstance that the air in our vessels, although pure at first, underwent a sudden chemical change when it came in contact with the blood, or urine, or grape juice; that the oxygen became converted into carbonic acid gas, and that, in consequence, hemi-organism could no longer exercise its force. We are astonished at this assertion, for M. Fremy must be aware that, since 1863, we have given analyses of the air in our vessels after they had remained sterile for several days—for ten, twenty, thirty, or forty days—at the highest atmospheric temperatures, and that oxygen was still present, often even in proportions almost identical with those to be found in atmospheric air.[185] Why has M. Fremy made no allusion to these analyses? This was the chief, the essential point in question. Besides, if M. Fremy had wished to test the truth of his explanation, there was a very simple means of restoring the purity of the air in contact with the liquids open to him; he might have passed through his vessels a slow and continuous current of pure air, day and night. We have done this a hundred times, and we have always found that the sterility of the putrescible or fermentable liquids remained unaffected.

The hemi-organism hypothesis is, therefore, absolutely untenable, and we have no doubt that our learned friend will eventually declare as much before the Academy, since he has more than once publicly expressed his readiness to do so as soon as our demonstrations appear convincing to him. How can he resist the evidence of such facts and proofs? Persistence in such a course can benefit nobody, but it may depreciate the dignity of science in general esteem. It would gratify us extremely to find the rigorous exactness of our studies on this subject acknowledged by M. Fremy, and regarded by that gentleman with the same favour bestowed upon it everywhere abroad. It may be doubted if there exists at the present day a single person beyond the Rhine who believes in the correctness of Liebig’s theory, of which M. Fremy’s hemi-organism is merely a variation. If M. Fremy still hesitates to accept our demonstrations, the observations of Mr. Tyndall may effect his conversion.

The other publication to which we alluded was the work of the celebrated English physicist, John Tyndall. It was read before the Royal Society of London, at a meeting held on January 13, 1876.

The following letter explains how the illustrious successor of Faraday at the Royal Institution came to undertake these researches:—

“London, February 16, 1876.

“Dear Mr. Pasteur,—

“In the course of the last few years a number of works bearing such titles as ‘The Beginnings of Life’; ‘Evolution and the Origin of Life,’ &c., have been published in England by a young physician, Dr. Bastian. The same author has also published a considerable number of articles in different reviews and journals. The very circumstantial manner in which he describes his experiments, and the tone of assurance with which he advances his conclusions, have produced an immense impression on the English as well as the American public. But what is more serious still, from a practical point of view, is the influence that these writings have exercised on the medical world. He has attacked your works with great vigour, and, although he has made but slight impression on those who know them thoroughly, yet he has succeeded in producing a very great and, I may add, a very pernicious one on others.

“The state of confusion and uncertainty had come to be so great that, about six months ago, I thought that I should be rendering a service to science, and at the same time performing an act of justice to yourself, in submitting the question to a fresh investigation. Putting into execution an idea which I had entertained for some six years, the details of which were set forth in an article in the _British Medical Journal_, which I had the pleasure of sending you, I have gone over a great deal of the ground on which Dr. Bastian had taken his stand, and, I believe, refuted many of the errors by which the public had been misled.

“The change which has taken place since then in the tone of the English medical journals is quite remarkable, and I am inclined to think that the general confidence of the public in the exactness of Dr. Bastian’s experiments has been considerably shaken.

“In taking up these researches again, I have had occasion to refresh my memory by another perusal of your works; they have revived in me all the admiration which I experienced when I first read them. It is my intention now to pursue these researches until I have dissipated any doubts that may be entertained in respect to the unassailable exactness of your conclusions.

“For the first time in the history of science, we are justified in cherishing confidently the hope that, as far as epidemic diseases are concerned, medicine will soon be delivered from empiricism, and placed on a real scientific basis; when that great day shall come, humanity will, in my opinion, recognise the fact that the greatest part of its gratitude will be due to you.

“Believe me, ever very faithfully yours,

“JOHN TYNDALL.”

We need scarcely say that we read this letter with the liveliest gratification, and were delighted to learn that our studies had received the support of one renowned in the scientific world alike for the rigorous accuracy of his experiments as for the lucid and picturesque clearness of all his writings. The reward as well as the ambition of the man of science consists in earning the approbation of his fellow-workers, or that of those whom he esteems as masters.

Mr. Tyndall has observed this remarkable fact, that in a box, the sides of which are coated with glycerine, and the dimensions of which may be variable and of considerable size, all the particles of dust floating in the air inside fall and adhere to the glycerine in the course of a few days. The air in the case is then as pure as that in our double-necked flasks. Moreover, a transmitted ray of light will tell us the moment when this purity is obtained. Mr. Tyndall has proved, in fact, that to an eye rendered sensitive by remaining in darkness for a little, the course of the ray is visible as long as there are any floating particles of dust capable of reflecting or diffusing light, and that, on the other hand, it becomes quite obscure and invisible to the same eye as soon as the air has deposited all its solid particles. When it has done this, which it will do very quickly in two or three days, if we employ one of the boxes used by Mr. Tyndall—it has been proved that any organic infusions whatever may be preserved in the case without undergoing the least putrefactive change, and without producing bacteria.

On the other hand, bacteria will swarm in similar infusions, after an interval of from two to four days, if the vessels which contain them are exposed to the air by which the cases are surrounded. Mr. Tyndall can drop into his boxes, at any time he wishes, some blood from a vein or an artery of an animal, and show conclusively that such blood will not, under these circumstances, undergo any putrefactive change.

Mr. Tyndall concludes his work with a consideration of the probable application of the results given in his paper to the etiology of contagious diseases. We share his views on this subject entirely, and we are obliged to him for having recalled to mind the following statement from our _Studies on the Silkworm Disease_:—“Man has it in his power to cause parasitic diseases to disappear off the surface of the globe, if, as we firmly believe, the doctrine of spontaneous generation is a chimera.”

THE END.

Footnote 185:

See _Comptes rendus_, vol. lxi., p. 734, 1863.

INDEX.

A

Absorption of gases by air-free liquids, 292 oxygen by blood, 50; by urine, 50 from solutions by _bacteria_, 295

Acidity, natural, of wine a preservative, 2, and footnote of beer heated, 20 action on ferments, 35

Acetate of lime from fermentation of tartrate, 288

Acid, sulphuric, facilitating filtration, 250

Acid, carbonic, _v._ carbonic acid

Adaptability of liquids to certain growths, 36, 73, 85 (supposed) of vibrios to aërobian or anaërobian conditions, 309, 310

Aeration, reviving influence of, 138 adoption by brewers of, 253 tardy, of wort in deep vessels, 348 on “coolers,” its importance, 348, 349

Aeration-conditions in ordinary brewing process, 350, 351, 364, 365

Aeration of wort, apparatus for regulating, 352

Aeration, influence on clarification of worts, 381 experiments on its influence on growth, 107, 130

Aërobian, definition, 116 ferment, growth of, 208, 209 ferments, general characteristics, 210; origin of, 210 (footnote); cultivation of, 211; aspects of, 212-217; distinguishing features of, 218 life in ferments overlooked, 260

“Age,” as applied to a ferment, 169

Age of cells, 246

Aged aspect of exhausted cells, 133, 147

Air, influence on ferment-life, 242 renewal of, in brewers’ yeast, 246, 247 mode of expulsion from growing media, 285 unnecessary to life of _vibrios_, 292 injurious to life of _vibrios_, 304

Air, compressed, and ferment-life, 324 composition unaffected by contact with blood, &c., 398

Albumen-transformation theory of fermentation, 273

Albuminous liquids, growth of yeast in, 265

Alcohol, percentage is heated beer, 20

Alcoholic ferment, minute species of, 71

Alcohol, detection in minute quantity, 78, 79 (footnote) produced by _penicillium_, 99, and following pages by _aspergillus glaucus_, 101, and following pages by _mycoderma vini_, 111, 113 explanation of, 114

Alcoholic fermentation, general explanation of, 114, 115

Alcohol, proportion of, to mucor forming it, 134, and following pages

Alcohol produced by moulds, 258 (footnote) production of, within fruits, 267

Alcoholic fermentation, restricted meaning, 275 (footnote) necessary relation with yeast-cells, 275

_Altenaria tenuis_, 157

Ammonia, a test for vegetable organisms (Robin), 312

Ammoniacal urine, 45, 46

Anaërobian, definition, 116 growth of yeast, 239, and following pages precautions to be observed in, 248 life of fruit-cells, 272 growth of _vibrios_, 302

Animal or vegetable nature of organisms, 312, and following pages

Anti-ferments, 45

Apparatus for sterilizing liquids, 27 for producing pure beer, 340, &c. for pure pitching, 344 for pure aeration, 352 for cooling beer with regulated supply of pure air, 388, 389

Appert’s experiment, 62

Aroma of beer destroyed by excess of air, 353

Asbestos, useful plug, 27, and footnote, 30

Ascospores of yeast, 150 (footnote)

Aspect of yeast variable, 37

_Aspergillus glaucus_, functioning as ferment, 101, and following pages different aspects of, 105

Atmospheric germs, 6, 26, 38 variety of, 39, 76, 87 (footnote)

_Autonomy_ of organisms, 84 (footnote)

B

Bacteria, 35, 36; medium for growth of, 294; absorption of air from solutions by, 295

Bacteria and butyric vibrios, how related, 296 influence of oxygen upon, 305

Bail mentioned, 92, 93, 127

Balling saccharometer explained, 363 (footnote)

Barley-wine, 1 (footnote), 230

Barley decoctions, experiments on development of ferments in, (Fremy) 273 (footnote)

Bary, De, mentioned, 92; on relations of yeast to other organisms, 180, 181

Bastian’s experiments, 403

Baudelot refrigerator, 387 (footnote)

Bavarian beer, 10

Béchamp’s _microzyma_ theory, 121 influence of air on fermentation, 178 (footnote)

Beer, definition, 1; difference between it and wine, 1 changeable nature of: effects upon brewing purposes, 2, 3 two kinds only, “high” and “low:” difference, 7 samples of bottled, examined, 222 general precautions for pure manufacture of, 338 improved apparatus for commercial production, 340, and following pages

Beet root preservation in pits, 269 (footnote)

Berkeley mentioned, 92

Bellamy’s researches on fermentation in fruits, 270

Berard on fermentation of fruits, 270, 271

Berthelot’s mode of isolating inverting constituent of yeast, 322 (footnote)

Bert, action of compressed air on ferments, 324

Birds, experiment upon, described, 309

Bistournage, 43 (footnote)

Bisulphite of lime used by bottlers, 15

Blood, study of sterilized, 49, 50

Blood-crystals, 50 (footnote)

Boiling sterilizes liquids, 34

Bottling needle, 372 (footnote)

Bottled beer, treatment of, 16

_Bouche_ influenced by presence of oxygen, 387

Bouchardat, 323

Brefeld, strictures on Pasteur’s theory criticised, 280 convinced of truth of Pasteur’s theory, 315, 316

Breweries, statistics of, 10

Brewing, change in processes of, 7 practices largely empirical, 222

Brewing processes under conditions of purity, 390

Budding, rate of, experiment on, 145 process of, 146

Buffon’s hypothesis mentioned, 121

Bulbs, glass, for study of growths, 156 (footnote) for vibrios, 298

Bunsen, tables of solubility of oxygen in water, 360

Butyric vibrios in must, 65; in wort, 70

Butyric acid from fermentation of lactates, 297 not a suitable food for vibrios, why?, 301 (footnote)

Butyric fermentations yield variable products, 308

C

Cagniard Latour, on cause of fermentation, 60

Calmettes, M., 369, 371; experiments on the curve of cooling of wort, 377, 378

Carbolic acid for purifying yeasts, 232

Carbonate of lime crystals formed in fermentation of lactate, 294

Carbonic acid, influence on preservation and fermentation of fruits, 268 evolution from fermentation of tartrate of lime by vibrios, 287 amount of evolution, 288 mode of collection of, 288 influence on bacteria, 305 (footnote)

Caseous ferment, occurrence, 200; aspect, 201; endurance of heat, 203 (footnote); meaning of title, 202; origin of in brewers’ high yeast, 203, 204; origin of in English pale ale, 204, 224; aërobian form of, 215

Cells, power of endurance, 134 aspect of dead, 139 (footnote)

Cells, glass, for study of growths, 155 (footnote)

Cells, probable function in elaborating proteic matter, 335

Cellulose, not soluble in ammonia (Robin), 312

Change of yeast, usual remedy for disease, 22

Chauveau on castration, 43

Circumstances modifying nature of germs present in atmosphere, 73, 87 (footnote)

_Cladosporium_, 55 (footnote)

Clarification of liquids by fungi, 66 (footnote) of wort, 381, and following pages of a wort and its beer not always correlated, 382, 383

Cohn’s medium for growth of vibrios, 294 (footnote)

Colour darkened by oxidation in pure liquids, 57

Coloration of vibrio-fermented liquors, 291

Colpoda, 39, 40

Composition of medium, influence on life, 296

Conidia, definition, 137

Conditions affecting the ferment character of cells, 266

Consumption of beer in France, statistics, 17 (footnote)

Contagion and ferments, 41, and following pages

Continuity, non-, of germs in air, 62

Continuous vital activity of cells, 278

Contact-action, theory of, 326

“Coolers,” importance in aeration of wort, 348, 349 influence on worts, 364

Cooling of wort must be rapid in ordinary brewing, 2 artificial of “low” beers, 12

Cooling of wort in presence of carbonic acid, 342; difficulties of the process, 346, and following pages

Corpuscles on grapes and stalks, 54

Corpuscles refractive in bodies of vibrios, 300, _v._ also cysts

Correlation of special germs with special fruits, 61 of special ferment and fermentation product, 277

Cotze and Feltz, 43

Crushers for the vintage, 268 (footnote)

Cream of tartar, _v._ tartrate

Cultivation of yeast under conditions of purity, 29-32 of pure penicillium, mode of, 88, and following pages of aërobian ferments, 211, and following pages

Cysts of vibrios, 306, 307

D

Davainne, on splenic fever, &c., 42

Daughter-cells, 146

Dead cells, aspect of, 139 (footnote)

Declat’s treatment of infectious diseases, 44

_Dematium_, 167; resemblance to _Saccharomyces pastorianus_, 179, 180, 181, 214 resemblance to “caseous” yeast, 201

Degrees, Balling, _v._ Balling

Deposits, amorphous, of wort, 6, 193, 385, and footnote

Deterioration of beer correlated with presence of foreign organisms, 26, 32

Differential vitality, a means of separating ferments, 226

Difficulty of experiments on growths, 63, 85

Disease-ferments, what they are, why so called, 4 classification and account of, 5, 6 origin of, 6 inactive at low temperatures, 14 often found only in deposits, 24 not everywhere in atmosphere, 31

Disease-germs usually latent, 220 development in bottled beer, 222

Diseases of wort and beer, meaning of, 19 mode of proving the cause of, 19, 20

Diseased beer always result of disease ferments, 26

Distribution of germs limited, 61

Division, fissiparous, of vibrios, 299

Dried yeast, 81

Dryness decreases sensitiveness of moulds to heat, 35

Dumas, distinction between organized and unorganized ferments, 323

Dust, atmospheric, contains disease-germs, 6, 26 on fruits, experiments with, 153, and following pages when fertile, 157, and following pages

Dutch yeast, 200

Duval, Jules, experiments on transformation of ferments illusory, 37

E

_Efflorescence_ of fermented liquors, 108, 117

Egg-albumen, experiments on, 51

Egypt, beer first brewed in, 17

Empiricism in ordinary brewing, 222

Energy stored by cells, 133, 134

Endogenous sporulation of yeast, 150 (footnote), 172

English beers all “high,” 7 temperatures and yeast employed, 8 (footnote) breweries, usages of, 8 (footnote), 14

Errors, causes of, _v._ experimental errors

Equations of fermentations variable, 276, 277

Examination of deposits, mode of, 21 (footnote)

Exhaustion, definition of, 171 (footnote)

Exhausted vibrios, 290

Experimental errors, 63, 85, 92 avoided by use of double-necked flasks, 120

Experiments, exactness of Pasteur’s, 95 (footnote) to prove connection between quality of ferment and quality of beer, 26, and following pages on living fluids, 47, and following pages comparative, on pure must and must with corpuscles boiled and unboiled, 54, and following pages by Gay-Lussac on must, 62, 63 by Pasteur after Gay-Lussac, 64 on distribution of ferments, 65, and following pages on distribution of fungus-spores, 68 in wide shallow dishes, 69, and following pages comparative on germs in air, 72, and following pages with non-fermentative species of _torula_, 78 on spontaneous impregnations, 65, 66, 69, 73, 79, 87 (footnote) on spontaneous fermentation, 184 on dried yeast, 81, and following pages on influence of aeration on growths, 107 on aeration and its absence, 130, and following pages on function of oxygen on ferment-life, 238, and following pages on the capacity of yeast for oxygen, 255 on influence of carbonic acid on fruits, 268 on growth of vibrios apart from air, 285 on fermentation of lactate of lime apart from air, 292, and following pages on influence of air on vibrio-life, 303, 304 on influence of air on bacterium-life, 305 on gradual adaptability of organisms to adverse life-conditions, 309 on influence of air on fermentation, 349 on solubility-coefficients of wort for oxygen, 361-3 of brewers’ worts, 366, and following pages on combination of oxygen with worts, 371, and following pages on the rapidity of the combination, 376 on amount of combination, 379 on non-transformation of _mycoderma vini_, 110, and following pages, 113 (footnote) of _mycoderma aceti_, 124, and following pages of _mucor racemosus_, 128, and following pages on non-transformation of yeast into penicillium, 333-335 on cultivating pure _penicillium_, 88, and following pages on its transformation into yeast, 91 transformation, Trécul’s, details of, 98 with submerged _aspergillus_, 101, and following pages _penicillium_, 99 in disproof of the _hemi-organism_ theory, 273 (footnote) on growth of mixed moulds, 112 on purification of mixed ferments, 226, and following pages on growth of _mucor mucedo_, 140, 141 on proportion between weights of mucor and alcohol formed, 134, and following pages on the anaërobian cultivation of yeast, 239, and following pages on variation of proportion of sugar used to yeast formed, 249 on growth of yeast in sugar solutions, 318, and following pages, 331-333 on dust on fruits, 153, and following pages on seasonal influences on fertility of dust-germs, 157, and following pages on exhaustion of yeast, 169, and following pages of “high” yeast, 189, 190 on revival of yeast, 207, 208 on cultivation of aërobian ferment, 211, and following pages on gradual _senescence_ of yeast, 245 on production of a pure beer, 338, and following pages on clarification of worts and beers, 382, and following pages comparative, on the qualities of beers brewed by different processes, 391 on rate of budding, 145

Exportation of “high” beers unsatisfactory, 16

F

Ferment, _v._ also yeast

Ferments of disease, _v._ disease-ferments

Ferments, special, 14, 15

Ferments and animal diseases, 41, and following pages butyric, lactic, alcoholic, 72 moulds functioning as, 100, 101, and following pages, 111, 113, 129, 133 general character of a, 115 of grape, varieties, origin, 150, and following pages alcoholic, summary of, 196 intermixture of, 224, 225 mode of separation of mixed, 226 and following pages succession of, in must, 227 exceptional vital processes of, 236, 237

Ferment power in relation to time discussed, 252 character, how related to heat, 270 and fermentation correlated, 277 a chemical substance existing in cells (Traube), 283 (footnote) of tartrate of lime, 290

Ferments, two classes, distinctive characteristics, 323

Fermentation, rapid, inexpedient, 3 spontaneous, in case of must, 4 “top” and “bottom,” _v._ “high” and “low” masked by moulds in shallow vessels, 75 (footnote) by _penicillium_ (Tréoul) 94 by _mycoderma vini_, 111, 113 by _mucor racemosus_, 129, 139 alcoholic, general explanation of, 114, 115 conditions of, in sweetened mineral liquids, 211 without air, 242 with and without air, results compared, 243, 244 a cell-life without air, 259 a general phenomenon, 266, 267 of fruits not truly “alcoholic,” 276 not definable, according to Brefeld, as life without air, 280 of lactate of lime, 294

Fermentative energy, 252 character dependent on conditions, 266

Filamentous tissue (Turpin), 123

Fitz on fermentation, 142

Fissiparous division of vibrios, 299

Flask sterilizing, 27, 29

Flasks with double necks, advantage of, 120

Fluid, Raulin’s, 88 (footnote)

Flavour dependent on ferment species, 230

Foreign organisms correlated with unsound beer, 26, 32 greatly promoted by adaptability of liquids, 36

Formula for solubility-coefficient of any wort for oxygen, 364

Fremy’s statement of _hemi-organism_, 52 answer to Pasteur’s facts, 58 explanation of vintage fermentation, 272 “organic impulse,” 325 latest assertions, 396-399

Fruits, ferment organisms on surface of, 153, and following pages internal fermentation of, 267, and following pages yeast cells not present within, 267 (footnote) influence of carbonic acid gas on preservation of, 268 respiratory processes of, according to Bérard, 270 fermentation within, Lechartier and Bellamy, 270 crushed and uncrushed, fermentation of, 274

Fruit-cells, anaërobian life of, 272

Fungi, wide distribution of spores, 68 absorption of oxygen by, 257 production of alcohol by, 258 (footnote)

Fungoid manner of growth of well-aerated yeast, 251

G

Galland’s claims of priority, 338 (footnote)

Gay-Lussac’s experiments on grape-juice, 59, 60

Gayon’s experiments on egg-albumen, 51

“Gathered,” 367 (footnote)

Generation, theories of, contrasted, 397

Germs of ferments in air, &c., 6, 26, 38 brought by other matters, 38 absent from fruits, when? 58, 59, 157, and following pages not universally distributed, 61, 63, 181 (footnote) distribution experiments, 65, and following pages, 87 (footnote) and their correlated fruits, 61 of disease latent, 220

_Germ_, use of term by Pasteur, 313

Germ theory of disease discussed, 46, 47

Globuline tissue (Turpin), 123

Globulines, punctiform, 121, and following pages

Globules, 275 (footnote)

Glycerine, fermentation of, by vibrios, 306, 307

Gosselin, M., report, 44 and Robin on ammoniacal urine, 45

Gramme, value in grains, 135 (footnote)

Granules in wort, explanation of, 95

Graham’s, Dr., criticisms of Pasteur, 13 (footnote), 196 (footnote)

Graham, Dr., on aspect of bottom yeast, 194 (footnote)

Grape juice, experiments on, 57, 59

Grape-ferments, _v._ ferments

Grapes, do they contain cells of yeast? 267

Greasiness of _mycoderma vini_, 80, and footnote

H

Hallier mentioned, 92

Hard water, influence on aspect of yeast, 194 (footnote)

_Head_ of vibrio, 292

Heating sufficient as preventing deterioration of liquids, 20 influence on beer, 20

Heat, production of, its relation to ferment-power, 270

_Hemi-organism_, chimerical, 53, 162, 399, 273 (footnote) latest assertions by Fremy on subject of, 396-399 theory of vintage-fermentation, 272, 273

Heterogenesis, facts against, 51

“High” fermentation, meaning of, 8, 9 beers, disadvantages of, 12, 13 ferment, aspect of, 188, 189 characteristics of, summary, 191 ferment (new), occurrence, 198 aspect and characteristics of, 199 aërobian form of, 216

High yeast, aërobian form, aspect of, 214

Hoffmann, H., transformation of ferment, 92, 93

Hop-oil as a beer-antiseptic, 16, and footnote

Hopping influence on growths _quâ_ temperature, 96

Hot countries, absence of breweries in 16

Hydrogen from vibrionic life, 300 occasional absence in butyric fermentations, 308

Hydrosulphite of soda, composition, use in determinations of oxygen, 355, and footnote preparation of _saturated_ solution, 357 (footnote) alterability of solutions of, 356 improved method of M. Raulin, 356, and following pages

I

Ice, quantities consumed in “low” breweries, 11

Illusions as to absence of foreign organisms, 36, 85, 92

Impregnations, spontaneous, 65, 66, 69, 73, 79

Impregnation, mode of (_penicillium glaucum_), 86

Impurity of ferments, source of experimental errors, 37 of yeast masked for a time, 220

Increase of yeast disproportionate to sugar used, 237

Infusions, nature of organisms in, 39

Infusoria, 35

Insoluble substances in wort, 386

Inverting constituent of yeast, 321, and footnote

Isolation of ferment, 77

L

Lactic ferments, 5, 36 transformation from and into other ferments (Duval), 37

Lactate of lime, fermentation of, 292

Lechartier and Bellamy, researches on fermentation in fruits, 270

Leptothrix, 36

Liebig’s views of fermentation, 317, and following pages on fermentation of malate of lime, 321 definition of a ferment, 324 modified theory, 326; answer to, by Pasteur, 326, 327 neglect of microscopical observations, 329, 330

Lime, bisulphite, use of, by bottlers, 15 carbonate sterilized, use of in growths, 126 dextro-tartrate, 284 acetate and metacetate, 288 lactate, fermentation of, 292

Lister’s, Prof., letter on germ-theory, 43

London breweries, usages of, 8 (footnote) Pasteur’s visit to, 22-24

“Low” fermentation, meaning of, 9, 10; advantages, 12 beer breweries, statistics of, 10 properties of, according to Dr. Graham, 13 yeast and “high” yeast distinct, 192, 193 yeast, aspect of, 193; characteristics, 195 aërobian form of, 215

Low temperatures prejudicial to disease-ferments, 14

M

Malignant pustule, 42

Mashings, 3

Medium, mineral, for growing lactic vibrios, 293, 297 (footnote) Cohn’s formula, 294 (footnote) for growth of bacteria, 294

Medium, composition of, influence on life, 296

Microscopical study of yeast important, 23 formerly neglected in English breweries, 22-24

Microscopical examination of vibrios, 298, 299

Microzyma, 121; source of _mycoderma aceti_ according to Béchamp, 124

Milk, temperature of sterilization of, 34

Milk-sugar, growth of yeast in, 265

_Mother of vinegar_, _v._ mycoderma aceti

Moulds thrive in acid liquors, 36 functioning as ferments, 100, 101, and following pages, 111, 113, 129, 133 growth of, and production of alcohol, 257, 258 (footnote) suggested employment of, industrially, 261

Mucedines, 36, 40

_Mucor mucedo_ and _racemosus_ on must, 66

_Mucor racemosus_, different aspects of, 105 pure growth of, 128, and following pages

Mucor normal, growth of, 132 weight of to alcohol formed, 134, and following pages morphology of abnormal growth, 137

_Mucor mucedo_ distinguished from _racemosus_, 140 growth in double-necked flasks, 140, 141

Müntz, 323

Must, fermentation of, always regular, 3 pure fermentation of, 54, and following pages succession of ferments in, 227, 228

_Mycelium_ and _mycoderma vini_ on wine, 56, 65

Mycoderma in wort experiments, 70

_Mycoderma vini_, arborescent form of, 77 growth of pure, experiments on, 110, and following pages, 120 growth with _penicillium_, 112 with _mucor_, 112 endogenous sporulation, 151 (footnote)

_Mycoderma aceti_ transformations (Béchamp), 124 pure growth of, 124, and following pages

N

_Nageurs_ used in low fermentation, 9

Nature of liquids, influence on growths, 36, 73, 85

Natural liquids for pure growths, use of, 40, 41 experiments on, 47, and following pages

Neutrality, conditions of, as affecting sterilization of liquids, 34; explanation of fact, 35

Neutralization of acidity in pure growths, mode of, 126

New high ferment, _v._ high

New process of brewing, 391-393

Nitrogenous soluble parts of yeast, 319, 320

Nomenclature used by Pasteur purposely vague, 314

Normal growth of mucor, 132

O

Organic substances, have they any tendency to become organized? 33

Organic liquids sterilized by boiling, 34

Organizable globulines (Turpin), 123

Organisms and animal diseases, 42

_Ouillage_, 2

Oxidation of germ-free liquids, 57 processes of fungi, 261, and footnote of wort, excessive, injurious, 353, 354

Oxygen absorbed by blood, 50 by urine, 50 and fermentation, according to Gay-Lussac, 60 store-energy imparted to cells by, 134 no influence upon fermentation, (Béchamp), 178 (footnote) function in fermentation, experiments on, 238, and following pages influence on fermentation (Schützenberger and Pasteur), 253, 254 amount absorbable by yeast, 255 deficiency of, function in fermentation, 259 influence on products, 100, 108, 113 influence on morphology of moulds and ferments, 105, 106, 133, 137, 262 necessity of, to growth of yeast discussed, 280 unnecessary and adverse to vibrionic life, 284, and following pages necessary to bacterial life, 305 removal from solutions by bacteria, 295 growth of vibrios apart from, 302 compressed, influence on ferment life, 324 determination of, in worts (Schützenberger), 355, and following pages solubility-coefficients in water (Bunsen), 360 usual amounts in solution in brewers’ worts, 366, 367 changes in amounts during brewing processes, 369, 370 combination of, with hopped wort, 371, and following pages experiments on rapidity of combination, 376 on amount of, under brewing conditions, 379 in combination with wort not available for yeast, 380, 381 clarification of wort by, 385

P

Palate-fulness definition, 354, and footnote impaired by oxidation, 354

Parasites and their germs, 40 influence on animal diseases, 41

Pasteur’s repetition of Trécul’s experiments, 98, 99 subject of his inquiries stated, 311 experiments, exactness of, 95 (footnote)

Pasteurization, meaning and use, 15 (footnote)

Patches of froth in growth of pure yeast, 31

_Penicillium glaucum_ on must, 66 growth of pure, 86, and following pages precaution, 89 transformed into ferment (Trécul), 94 spores, varieties of, 97 production of alcohol by, 99, and following pages transformation into mycoderma, 109

Phenol for purifying yeasts, 232

Pitching, mode of, for pure beer, 342, and following pages flasks, 344 peculiar in London breweries, explanation, 350, 351

Plaster of Paris and yeast powder, 81, and following pages

_Ploussard_ grapes, experiments on, 161

Polymorphism of organisms, 84 (footnote), also _v._ transformation

Precautions for pure fermentation of must, 64 brewers’, to check disease-germs, 220, and following pages for pure anaërobian growth of yeast, 248

Preservation of yeast, 207

Preoccupation of liquids by organisms, 36, 109, 220

Products of fermentation variable, 276, 277

Price of beer as affected by losses from disease, 24

Proliferous pellicles, 121

Proportions of alcoholic products variable, 276, 277

Proportions of products diagnostic of the fermentation, 279

Proteic matter elaborated by cells, 335

“Pulling up,” 343

Pure growth of yeast, precautions for, 29-32 growths in natural liquids, 40, 41 wort and ferment, advantages of, 391-393

Purification of mixed ferments, 226, and following pages practical methods, growth in sweetened water, 230 shallow basins, 231 in acid and alcoholic liquids, 231 with aid of carbolic acid, 232

Putrid wort, ferments of, 5

Putrefaction prevented by use of sterilizing flask, 27 of yeast, cause of, 221 of tartrate of lime, 291

Q

Qualities of “high” and “low” beers, 12, 13, 19, 196

Quality of beer dependent on kind of ferment, 26, and following pages

R

Racking, 222 precautions necessary in, 351

Raulin’s fluid, 88 (footnote) improvement on Schützenberger’s oxygen process, 356, and following pages experiments on solubility of oxygen in worts, 361-363

Rayer on splenic fever, &c., 42

Reducing action of vibrios, 291

Rees, Dr., 150 (footnote)

Refrigerator, Baudelot’s, 387 (footnote)

Revival of mould-cells by aeration, 130, 131 (footnote), 138

Revival of starved yeast, 148, 208 vibrios, 301, 302

Ripening of fruits, 270, 271

Robin, Ch., mentioned, 93; strictures on Pasteur, 310, 311 recantation of views on fermentation, 314

S

_Saccharomyces apiculatus_, 71, and footnote, 150 _exiguus_, 185, _ellipsoideus_, 165 _pastorianus_ 151; mode of growth of, 167 two aspects, globular and filamentous, 168, 169 exhaustion and revival of, aspects, 172, and following pages occurrence as impurity in most ferments, 225 most suitable for growth experiments in sugar solutions, 332

_Saccharomyces pastorianus_, _ellipsoideus_, _apiculatus_ in must, 227, and following pages

_Sang de rate_, 43

Schützenberger on budding of yeast, 146, and footnote

Schützenberger’s strictures on Pasteur’s views answered, 252, and following pages process for determining oxygen in solutions, 355

Seasons, influence on success in brewing, 25 at which germs are absent on fruits, 58, 59

Secondary fermentation in English beers, 224

_Senescence_ of yeast cells, 208 gradual of yeast cells, experiments on, 245

Shallow basins for purification of yeasts, 231

Sodium hydrosulphite, _v._ hydrosulphite

Solubility-coefficients of oxygen in water (Bunsen), 360 in worts (Raulin), 361-363

Sour beer, ferments of, 5

Soundness of beer always dependent on purity of yeast, 26, 32

Specialization of ferment-variations, 197

Specimens, necessary precautions for taking, 126 (footnote)

Splenic fever, 42

Spontaneous fermentation used in must, not in beer, 4 fermentation or putrefaction prevented by use of sterilizing flask, 28 ferment, definition of, 182; experiment on, 184 generation, facts against, 51, 52, 57 supported by experimental errors, 62, 63 (Trécul’s theory of), 94, 95 impregnations, 65, 66, 69, 73, 79 use in isolating ferments, 77

Spores on grapes, gooseberries, &c., 54 of fungi widely distributed, 68

Statistics of breweries, 10 of French beer consumption, 17 (footnote)

Starved yeast, appearance of, 148

Stability of sterilized liquids, 286

_Stemphylium_ spores, 55 (footnote)

Sterilizing apparatus, 27, 29, 285 flask, 28

Sterilization-temperature of various liquids, 34

Stock beer, 223

Store beer, must be surrounded by ice, 16

Straw wine, peculiar fermentation of, 166

_Strength_, Pasteur’s use of word, 354 saving by the new process, 394

Submerged _penicillium_, 99 _aspergillus_, 101, and following pages _mycoderma_, 111, 113, and following pages _mucor_, 129, and following pages, 133

Submerging growths, precautions for, 91 (footnote)

Succession of transformations (Trécul’s scheme), 93, 94

Sugar decomposition by submerged cells, 114 different modes of, by different cells, 115 decomposed disproportionate to yeast formed, 237, and following pages variation of disproportion in different cases, 249 amount decomposed in a given time, as an index of fermentative energy (Schützenberger’s views), 252 solutions pure with mineral salts, growth of yeast in, 317, and following pages denial of the fact by Liebig and reply by Pasteur, 328, 329

Surface growth of yeast in pure culture, 31

Sweetened water for exhausting yeast, 169, 170, 190 for purification of yeasts, 230

T

Tartrate-acid of potash for purifying yeasts, 231 -dextro of lime, fermentation of, 284, and following pages products of, 288 ferment of, 290

Temperatures in use in London breweries, 8 (footnote) high, prejudicial to quality of “low” beer, 19 at which disease-ferments perish, 20; differs in different liquids, 34, 96 influence on fermentation, 129

Temperatures suitable for “high” or “low” yeasts respectively, 192 influence of on mixed “high” and “caseous” yeasts, 203 for observing active vibrios, 299

Theories of generation opposite stated, 397

Tieghem, Van, on ammoniacal urine, 45

Torula, sense in which used, 73 (footnote) varieties of, 77 non-fermentative species, 78

Transformation of ferments, according to Duval, 37 of non-fermentative to fermentative impracticable, 80 of _penicillium_ into yeast impracticable, 91 of ferment into moulds (Hoffmann), 92 series, Trécul’s scheme of, 93, 94 of _penicillium_ to _mycoderma_ (Ch. Robin), 109 (footnote) of _mycoderma vini_ refuted, 113 (footnote) Turpin’s system of, 122, and following pages of _mycoderma aceti_ (Béchamp), 124 historical account of views on, 128 (footnote) of _mucor_ (Bail), 127 of filamentous into globular yeast, 169 of yeast into _penicillium_, &c., impracticable, 333-335 mutual of low and high yeast, discussed, 192, 193 of “high” yeast into “caseous” ferment illusory, 203 of albumen, theory of the vintage, 272, 273 theory disproved generally, 273 (footnote)

Traube, Dr., on ammoniacal urine, 46 researches on fermentation, 282 theory of fermentation, 283 (footnote)

Trécul and Fremy, _v._ Fremy

Trécul’s theory of successive transformations, 93, 94 details of transformation experiments, 98 theory refuted, 99

_Trousseau_ grapes, experiments on, 162

“Turned” beer, ferments of, 5; filaments of, 23

“Turning out,” 367 (footnote)

Turpin, M., mentioned, 92

Turpin’s system of transformations, 122, and following pages, 113 (footnote)

Tyndall, letter to Pasteur, 399-401

U

Unsoundness of beer correlated with disease-organisms, 26, 32

Urea-ferment, the transformation of (Duval), 37

Urine, ammoniacal, 45, 46

Urine, sterilized, study of, 49, 50

V

Variability of fermentation products, 277

Variations of ferment strengthened and established, 197

Varieties of yeast, 149, and following pages

Vaureal, De, budding of yeast, 146 (footnote)

Vegetable distinguished from animal organisms by ammonia (Robin), 312

Vesicular tissue (Turpin), 123

Vibrio, 36; butyric, 65, 70 also an example of anäerobian life, 282, 284 active and exhausted, 290 reducing action of, 291

Vibrionic ferment of tartrate of lime, 290

Vibrios, _head_ of, 292; supposed reproductive corpuscles, 306 growth of, in lactate media, 293 medium for growth of, according to Cohn, 294 (footnote) not genetically related to bacteria, 296 of butyric fermentation, description of, 298, 300 mode of examining microscopically, 298 fissiparous division of, 299 measurements of, 300 cannot live on butyrates, 301 (footnote) revival of, 301, 302; anaërobian growth of, 302 life of, destroyed by oxygen, 303, 304

Vigour of ordinary brewer’s yeast, 246

_Vin de paille_, 166

Vinegar, temperature at which it is sterilized, 34

Vinous flavour in stock beer, 224

Vintage, varied conditions of, 268 (footnote) fermentation, theory of, according to Fremy, 272, and following pages

Viscous wort, ferments of, 5

Visit to London brewery by Pasteur, 22-24

Vital processes of ferment exceptional, 237 activity of yeast apart from air, 259 potential in cells, 278

Vitiation of experiments, causes of, 63, 85, 92

W

Wad-dressing, antiseptic, 44

Water, hard, influence on aspect of yeast, 194 (footnote)

Weights of _mucor_ and alcohol, proportion of, 134, and following pages

Weight of yeast grown, what due to, 257 (footnote)

Wide dishes, experiments on fermentation in, 69, 70 favourable to mould developments, 75 (footnote)

Wine, less liable to deteriorate than beer, 2 temperature of sterilization, 34

Wort, definition, 2; cooling of, 3, 4 temperature of sterilization, 34 solubility of oxygen in, 361, and following pages formula for solubility in any wort, 364

Worts, brewers’, usual amounts of oxygen in solution, 366, 367 experiments on amounts, 379

Wort, hopped, its affinity for oxygen, 371, and following pages mode of transmitting it free of oxygen, 371, 372 insoluble substances in, 386

Y

Yeast, _v._ also ferment, germs, torulæ nature and properties of, 143, and following pages starved and well-nourished, appearances contrasted, 147, 148 varieties of, 149, and following pages commercial origin of, where? 187 relations to other organisms, 180, 181 commercial mixtures, 224, 225 practical purification of, 230-233 impurities in masked for a time, 220 exceptional characteristics of, 237 growth of in sterilizing flasks, 29-32 not transformable into any other organism, 37 aspect may change under modified circumstances, 37 non-transformation of _mycoderma vini_ into, 120 _mucor_ into, 132 non-fermentative species of, 79, 80, 206, 207 “high,” characteristic aspect of, 188-192 well aerated, fungoid mode of growth, 251 anaërobian growth, cause of fermentation, 259 growth of, in solutions of sugar, 318, and following pages growth in relation to proportion of sugar used, 237, and following pages difficult propagation in saccharine mineral media, 329, 330 growth of, without producing alcohol, 265 capacity of absorbing oxygen, 255 necessity of oxygen for its growth discussed, 280 incapable of using oxygen in combination in worts, 380, 381 soluble nitrogenous part of, 320, 321, 79 (footnote) dried into dust still active, 81, and following pages does not perish at temperatures at which disease-ferments do, 20 sudden inactivity of, cause and cure, 347 (footnote) change of, a trade custom, 22 reason of addition of yeast to wort, 3 proportion commonly added, 3 reason of the large proportion used, 343.

Yeast-cells abundant in brewing laboratories, 75 gradual senescence of, 245

Yeast-cells, mode of examining fruits for, 267 (footnote) necessary relation to “alcoholic fermentation,” 275

Yeast-water, definition, 79 (footnote) exhaustion of yeast by, 171 use of in pure growths (_penicillium_), 88

“Youth” of cells, 246

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● Transcriber’s Notes: ○ Missing or obscured punctuation was silently corrected. ○ Inconsistent spelling and hyphenation were made consistent only when a predominant form was found in this book. ○ Text that was in italics is enclosed by underscores (_italics_). ○ Text that was in bold face is enclosed by equals signs (=bold=). ○ Footnotes have been moved to follow the chapters in which they are referenced. ○ Subscripts are transcribed by an underscore and a value enclosed in braces, such as O_{2}. Superscripts are transcribed by an up-caret and a value enclosed in braces, such as MC^2, or sometimes by an up-caret and a single character, such as 4^e.

End of Project Gutenberg's Studies on Fermentation, by Louis Pasteur