CHAPTER II.

On the Causes of the Diseases which affect Beer and Wort.

From our preceding observations it will be evident that the manufacture of beer, the arrangement of breweries, and all the processes practised by the brewer immediately depend upon this fact, that beer and wort are fluids essentially liable to change. Thus it becomes a matter of extreme importance that we should have an exact knowledge of the causes and nature of the changes which affect our produce, and it may be that this knowledge will lead us to regard the conditions of the brewing industry from a novel point of view, and bring about important modifications in the practices of the trade. We might vainly search the numerous works which have been written on brewing for information respecting the proposed subject of these studies. At the most we should find the diseases to which beer is liable in the course of its manufacture, or afterwards, vaguely hinted at; perhaps we might be favoured with certain empirical recipes for disguising the evil effects of those diseases.

It will be our endeavour to demonstrate the truth of the proposition we have already laid down, that every change to which wort and beer are liable is brought about solely by the development of organic ferments, whose germs are being perpetually wafted to and fro in the dust floating through the air, or distributed over the surface of the different materials and utensils used in brewing, such as malt, yeast, water, coolers, vats, tubs, casks, shovels, workmen’s clothes, and innumerable other things.

It is evident that this proposition bears a marked resemblance to the one which we have demonstrated concerning the diseases of wine.[16]

By the expression _diseases_ of wort and beer, we mean radical changes which so affect the nature of those liquids as to make them unpalatable, especially if they are kept; such changes produce beer which is sharp, sour, turned, oily, putrid, and otherwise bad. It would be unreasonable to apply the term _disease_ to certain modifications in the quality of beer, which may be produced by practices more or less commendable. Such modifications, too, may result from want of skill in the brewer, from the composition of the wort, from the specific nature of the yeast, or from the inferior quality of ingredients. It is a well-known fact that “low beer,” if manufactured according to the ordinary process, has not that same delicacy of flavour which characterizes beer fermented at a lower temperature than 10° C. (50° F.). Fermented at 10° C. (50° F.), or 12° C. (53° F.) or at a higher temperature, it loses the peculiar properties which consumers prize. Nevertheless, in point of soundness it may be as good a beer as one which has been fermented at 6° C. (43° F.), or 8° C. (46° F.). One might say of the former beer that it is inferior to the latter in estimation; but we could not rightly call it diseased, for we are supposing a case in which disease does not actually exist.

§ I.—Every Unhealthy Change in the Quality of Beer coincides with a Development of Microscopic Germs which are alien to the Pure Ferment of Beer.

Our proposition concerning the causes of the diseases of wort and beer might be demonstrated in several ways. The following is one of the simplest:—Take a few bottles of sound beer, say, for instance, that which is known in Paris as Tourtel’s, Grüber’s, or Dreher’s, from the name of the brewer who manufactures it. Place some of these bottles in a hot-water bath and raise the temperature to about 60° C. (140° F.). Permit them to cool, and then place them by the side of the other bottles that have not been heated. In every case, especially if we conduct this experiment in summer, we shall find that in the course of a few weeks—the length of time varying according to the temperature and the quality of the beer—all the bottles which have not been heated will have become diseased, in some cases even to the extent of being undrinkable. Let us next examine, by way of comparison, the deposits in the heated and non-heated bottles. We shall find associated with the pure alcoholic ferment other organisms, filiform and for the most part very slender, and either simple or articulated, as represented in Plate II., the design of which is taken from actual deposits occurring in beer that had been kept for some time at the ordinary temperature. A number of bottles of beer which had been heated on October 8th, 1871, were compared with those of an equal number of bottles of the same beer which had not been heated. The examination took place on July 27th, 1872. The beer, which had been heated to 55° C. (131° F.), was remarkably sound, well flavoured, and still in a state of fermentation. As a matter of fact, we have proved by exact experiments that alcoholic ferments, heated in beer, can endure a temperature of 55° C. (131° F.), without losing the power of germination; but the action is rendered somewhat more difficult and slower. Diseased ferments, however, existing in the same medium, perish at this temperature, as they do in the case of wine. The beer which had not been heated, had undergone changes which rendered it quite undrinkable. Its acidity, due to volatile acids, was higher than that of the other beer in the proportion of 5 to 1. The beer which had been heated contained ½ per cent. of alcohol more than the other.

The deposits in the heated bottles also showed filaments of disease, but in such minute quantity that it was necessary to search many fields of the microscope to discover their existence. Those which we found after the heating must have existed in the beer before that operation; the heat had destroyed them, without sensibly altering their shape or size; they could neither multiply nor continue to exert any influence upon the components of the beer.[17]

From these experiments we may easily perceive, on the one hand, that beers apparently sound to the taste do not contain these or any other filiform ferments, save in a scarcely appreciable quantity; and, on the other hand, that these same ferments appear with the first unfavourable change in the quality of the beers, and that they exist more or less abundantly in proportion to the intensity of disease.

In certain extremely rare cases it may happen—so, at least, we have been assured, but we have not proved the fact ourselves—that beer may keep sound in bottle, even without the preliminary heating. This exception can only occur in the case of certain beers of a peculiar composition, which are highly hopped, and are made during the favourable months of November or December, out of the choicest materials, and fermented with yeast that happens to be pure. In the deposit of such beer, even after a lapse of several months or several years, we should find only the ordinary alcoholic ferment, the slow action of which would merely cause a gradual increase in the quantity of alcohol existing in the beer, and a diminution in the proportion of dextrine. This beer might grow old, as wine does, and remain perfectly sound.

Very often the whole work of the brewer is jeopardized by the unsuspected presence of diseased ferments, a remedy for which is only devised after the evil has evoked the complaints of customers. In such a case the brewer avails himself of the kindness of some other brewer to obtain a change of yeast—a custom which is recognized and valued in the trade, since all managers of breweries have an interest in keeping it up. The brewer whose produce is most satisfactory recognizes the fact that unforeseen circumstances may compel him at any moment to change his yeast.

We have frequently had occasion to show that this necessity for a change of yeast depends, in most cases, on some change brought about by the presence of diseased ferments, the multiplication of which has resulted fortuitously from some unconscious neglect during the process of brewing, or from climatic influences. When we reflect that yeast is a living being, and that the medium which serves as its aliment, and the water in which it lives, are remarkably well adapted for the development of a vast number of other microscopic beings, the comparative purity of yeast should surprise us even more than its deterioration does.

Now by means of microscopical observations we might often detect the existence of the evil long before we are warned of it by a defective working, which invariably entails great losses.[18]

In proof of this remark we may cite the following facts. In the month of September, 1871, we were permitted to go through a large London brewery, in which the microscopical study of yeast was altogether unknown. We were allowed to make certain experiments in the presence of the managers of the establishment. We first examined porter yeast, which was collected in a channel that received the yeast as it worked out of the fermenting vessels. One of the ferments of disease abounded in this yeast, as may be seen in the accompanying sketch, which was taken on the spot (Fig. 1). It was evident that the working of the porter was extremely unsatisfactory, and had, perhaps, been so for a long time; indeed, we were told that they had obtained a change of yeast from another London brewery that same day. We made a point of examining this yeast with the microscope. It was beyond comparison purer than the preceding yeast.

It is evident that if these brewers had been in the habit of using the microscope they might have detected the unsoundness of their produce before the time when they actually made the discovery, which, no doubt, was forced upon them by the complaints of their customers, or some other annoying circumstance, that led to their obtaining a change of yeast.

We next obtained permission to examine the yeast of the other beers undergoing fermentation, especially those of white beers, such as ale and pale ale.

In the sketch which we made of these yeasts one may detect the presence of the filaments peculiar to turned beer (Fig. 2).

We examined with much interest the ales which had immediately preceded those undergoing fermentation, the yeast of which we had just inspected. We were furnished with two kinds, both in casks, the one fined, the other not fined. The latter was visibly turbid, and, examining a drop of it, we discovered three or four filaments present in every field of the microscope. The ale which had been fined was nearly clear, but wanting in brilliancy; it contained about one filament to the field. We asserted in the presence of the head brewer, who had been summoned, that these ales were extremely liable to change, that it was highly necessary to dispose of them without delay, and that they were necessarily already faulty in flavour—a fact which all admitted after some hesitation—attributable, of course, to the natural reluctance which every manufacturer feels to own that his produce is not above reproach. We were shown some of the finings used in the brewery; they were swarming with the same filaments of disease-organisms.

We then propounded to the managers certain questions on the subject of the losses which a brewery may sustain from changes in its beer. We had heard from several brewers that the selling price of beer differed so greatly from the cost of its production solely in consequence of the losses which the unavoidable waste of large quantities of beer was constantly causing; several brewers have in our presence estimated these losses at 20 per cent. of the total production, on the average.

At first the English brewers returned somewhat vague answers to our questions; however, after what had taken place, they doubtless recognized the fact that a mutual understanding between a savant and a practical man may often be of considerable benefit to the latter, and in the end they confessed to us that they had stowed away in their brewery a large quantity of beer which had gone bad in cask a fortnight or so after it was brewed. Having avowed thus much they expressed their great anxiety to learn the cause of so serious a change in their beer, which was quite undrinkable. We examined it under the microscope, without being able to detect immediately any diseased ferments, but being aware that the beer had probably been clarified, by remaining undisturbed for a very long time, and that these ferments might have become inert and precipitated to the bottom of the enormous vats containing the beer, we examined the deposits which had formed at the bottom of these vats. They were composed solely of filaments of disease-organisms, without even the least trace of the globules of alcoholic yeast. The supplementary fermentation of this beer had evidently been nothing but a diseased fermentation.

The resemblance between these filaments and those which, in considerably smaller proportion, accompanied the globules of alcoholic ferment in our preceding observations, the change in the beer, which was almost as bad as beer could possibly be, along with an abundance of filaments, and the change, to a minor extent, in that beer which only presented a few filaments in a field of the microscope, impressed those managers of the brewery who were present with an entire belief in the theory which we had been endeavouring to impress on their minds concerning the causes of the badness of their beer. Some eight days afterwards we paid another visit to this same brewery, and learnt that the directors had lost no time in acquiring a microscope, and in procuring changes of yeast for all the varieties of beer, which they had put in working since our first visit.

There are some periods of the year—early spring, summer, and autumn, for instance—when the working of a brewery is a matter of great difficulty. The preservation of yeast becomes a subject requiring the most delicate treatment, in consequence of the increase in the temperature. In the early part of autumn the most important ingredients used in brewing are of inferior quality; the deteriorating influences which have been at work have covered them with a variety of parasites. All these circumstances contribute to facilitate the development of diseased ferments.

§ II.—The Absence of Change in Wort and Beer Coincides with the Absence of Foreign Organisms.

The method which we have just pursued in demonstrating the existence of a relation between the diseases of beer and certain microscopic organisms can scarcely leave a doubt, it seems to us, as to the correctness of the principles which we are advocating. In every case where the microscope reveals in a yeast, especially a yeast which is in a state of activity, products which are foreign to the composition of alcoholic ferment, properly so called, the flavour of the beer is more or less unsatisfactory, according to the abundance or nature of these minute organisms. Moreover, when a finished beer of superior quality loses in the course of time its agreeable flavour, and becomes sour, it may readily be shown that the alcoholic ferment in the deposit existing in bottles or casks, although originally pure, at least in appearance, becomes gradually intermixed with these same filiform ferments or other ones. These facts may be deduced from what precedes; nevertheless, some prejudiced minds might perhaps urge that these foreign ferments are the consequence of some diseased condition, produced by circumstances of which we know nothing.

Although this gratuitous supposition may be difficult to sustain, we shall endeavour to corroborate our preceding observations by the method of experiment which will be seen to be the more decisive.

This method consists in proving that beer never possesses any unpleasant flavour, so long as the alcoholic ferment, properly so called, is not associated with foreign ferments; that this also holds good in the case of wort, and that wort, liable to change as it is, may be preserved in a state of purity, if it is kept under conditions that protect it from the invasion of microscopic parasites, to which it presents not only favourable nutriment, but also a field for development.

By employing this second method we shall, moreover, have the advantage of proving with certainty a proposition that we just advanced, and showing that the germs of these organisms proceed from the particles of dust which the common air wafts about and deposits on every object, or which are spread over the utensils and materials used in a brewery, materials that are naturally charged with microscopic germs, which various changes in the store-houses and maltings may multiply to an indefinite extent.[19]

Let us take a glass flask having a long neck (Fig. 3 A), and holding from 250 c.c. to 300 c.c. (_i.e._, about 9 or 10 fl. oz.); let us put into it some wort, hopped or not, and then draw out the neck of the flask in the flame of a lamp, so as to give to it the shape B (Fig. 3); let us next heat the liquid to the boiling point, when the steam will rush with a hissing sound out of the curved end. We may then, without further precaution, permit our flask to cool, or, as an additional safeguard, we may introduce a small quantity of asbestos into the open extremity, at the very moment when the flame is taken away from the flask. Before introducing the asbestos, we may pass it through the flame, and we may repeat this after it has been placed in the end of the tube.[20] The air which first re-enters the flask must come in contact with the heated glass and the hot liquid, and these will destroy the vitality of any germs existing in such particles of dust as this air may introduce. The re-entrance of the air will be effected very gradually—sufficiently so to enable the drop of water which the air, as it enters, forces up the curved tube, to catch all particles of dust. Ultimately, the tube will become dry, but then the passage of the air will proceed so slowly that every foreign particle will get deposited on its interior sides.

Experience tends to prove that external particles of dust cannot find their way into flasks of this pattern, having free communication with the air, at all events within ten or twelve years—the longest time that has been devoted to experiments of this kind; the liquid in the flasks, if originally clear, will not become in the least degree contaminated, either upon its surface or throughout its bulk, although the outside of the flasks may be covered with a thick coat of dust. This is an undeniable proof of the impossibility of particles of dust finding their way inside such flasks.

Wort treated thus will preserve its purity for an indefinite time, notwithstanding its extreme liability to rapid change when exposed to the air, under conditions which cause it to come in contact with the particles of dust that air contains. This also holds good in the case of wine, beef-tea, the must of grapes, and, generally speaking, of all liquids which are subject to putrefaction or fermentation, and which possess the faculty, when their temperature is raised to about 100°C. (212°F.), of destroying the vitality of those microscopic germs that are found in dust.

A flask such as we have described (Fig. 3) is all that we require when we have to demonstrate the facts that we have just reviewed, a more detailed account of which may be found in our Memoir published in the _Annales de Chimie et de Physique_, for 1862, under the title _Mémoire sur les corpuscules organisés en suspension dans l’atmosphère. Examen de la doctrine des générations spontanées._ The shape of the flask represented in Fig. 4 only differs from that of the preceding one in having a second little tube attached to the globular part of the flask; this presents great advantages for different objects of study, and it was adopted in the subsequent investigations detailed in this work.

This flask will permit us to study without difficulty every separate kind of microscopic organism in the liquid best adapted to it without fear, if we take reasonable precautions, that the subject of our study may become associated with other organisms, the accidental presence of which cannot fail to seriously affect the results of our observations.

Let us use one of those flasks in our experiment on yeast, at the same time expressly assuming that the minute germs of yeast are free from all contamination by foreign germs, an object which we shall learn how to realize by a variety of methods in a subsequent chapter.

Let us introduce some wort into our flask (Fig. 4); then, after we have fitted an india-rubber tube to the little supplementary tube, let us boil the liquid; the steam, finding an easier exit through the india-rubber opening than through the drawn-out tube, will rush out through the india-rubber tube, and thus, as it passes, destroy any germs which may be adhering to the sides of the little supplementary tube. If we close the india-rubber tube by means of a glass stopper, the steam will immediately issue through the bent tube. On permitting the flask to cool, it will then be ready for impregnation. If there were any fear that some foreign germ of an unknown nature might have effected an entrance during cooling, or had not been destroyed by the steam (which is always a little super-heated, in consequence of the resistance which it meets in escaping), we need only place the flasks on a warm stove, and leave them there for a few days or a few weeks to ascertain whether the liquid in them has undergone any change. We should then only use those flasks which contain a sound liquid.

At the same time we must warn our readers that this cause of error does not exist once in a thousand times, especially if we use an asbestos stopper to prevent the entrance of little insects which are attracted by the odour of the liquid, and which instinctively seek to enter at the extremity of the tube, and to pass through it into the flask. In going so far, and incurring such labour in search of their food, they condemn themselves to certain death, for they are sure to be drowned, since it would require an intelligence superior to that which they possess to enable them to get out of the flask; the liquid, morever, could not fail to undergo some change, in consequence of the particles of dust that the insects would introduce into it.

After having passed the flame of a spirit-lamp quickly over the india-rubber tube, the glass stopper, the curved tube, and even over the fingers of the operator, we may withdraw the glass stopper, and introduce the pure yeast by means of a glass pipette that has been previously heated. This yeast is kept in a vessel also free from the dust floating in the air. However few globules of yeast the glass tube may take up, it is sure to introduce a hundred or a thousand times more than is necessary for the impregnation of the liquid. The glass stopper must then be replaced immediately, after having been again quickly passed through the flame. In transferring our yeast from the vessel containing it to the flask, by means of a glass pipette, it is exposed to another cause of impurity, since we cannot avoid bringing it in contact with the common air. If this risk frequently troubled us in our experiments, we might banish it or minimize it by some new arrangement; but this is unnecessary. We have suffered no inconvenience from this cause, as there does not exist in the atmosphere anything like a continuous supply of that from which the so-called _spontaneous_ generation arises, as was erroneously believed to be the case before the publication of our Memoir in 1862, to which we have already alluded.

The following are the results of the experiments conducted in the manner just described.

The yeast which we sowed, in ever so small a quantity, seemed to acquire vigour, to bud, and to multiply. Soon, that is to say in the course of twenty-four or forty-eight hours or longer, according to the temperature, and, more especially, the degree of vitality in the globules, we found that the sides of our flasks were covered with a white yeasty deposit, and noticed on the surface of the liquid a fine froth, which at first appeared like little islets formed by groups of bubbles so minute that they would have been imperceptible had they not been joined together. These patches increased in size, and gradually attached themselves to each other, finally forming a thick froth. In the course of two or three days this froth fell, the fermentation proceeded less rapidly, and then ceased completely. The beer was finished. This beer might be preserved for an indefinite period in the flask without undergoing any change. The external air passes freely into and out of the flask, as the pressure of the atmosphere and the temperature vary, and the beer in the course of time becomes flat; it acquires age in much the same manner as wine does, but it never contracts any taste of disease, it never becomes sour, or sharp, or bitter, or putrid; it does not even become covered with _mycoderma vini_ as is usually the case with all beer exposed to the common air in the course of trade.

After some weeks, or perhaps months, a white ring may show itself on the surface of the liquid on the glass. This is a crown formed by a mass of young yeast globules, which grow there like a mould, by absorbing the oxygen of the air as it enters the flask. The bulk of the yeast which has been fermenting remains at the bottom of the liquid in the form of an inert deposit. This inertness, however, is apparent rather than real; the globules may be internally active, without any development of new buds, and the effects of this working may cause them to become more and more languid, and in the course of time may even destroy them.

The case is quite different when the yeast with which our wort is impregnated, instead of being pure, is mixed to any extent whatsoever with diseased ferments. Should there be any of these in the yeast with which we impregnate our wort, even though their quantity were so infinitesimal that the most skilful observer could scarcely discover them with the microscope, they would multiply in the flask after the beer had been finished, especially if the beer were left for a short time on a stove. In this manner we may secure an excellent test of the original purity of the yeast which we employ in the impregnation of our wort.

Thus it may be seen that the absence of microscopic organisms that are foreign to the nature of pure yeast may invariably be noticed in the case of a beer which is sound, and which will remain sound for any length of time, when in contact with pure air, at any temperature. We may see, too, that the presence of these organisms may invariably be detected in an unsound beer, the peculiar unsoundness of which depends upon the peculiar species of the organisms contained in it. It would be difficult to adduce clearer proofs than those which we have given as to the intimate relation existing between these organisms and the deterioration of beer. The relation between cause and effect, in the succession of physical phenomena in general, is established by proofs that are by no means more decisive.

Footnote 16:

A statement of this proposition, as far as it concerns beer, appeared first in outline in the author’s _Etudes sur le vin_, published in 1866.

Footnote 17:

As the deposit in the heated bottles is, as a rule, inconsiderable, it is necessary to exercise some precaution in collecting it. The bottles are taken up; after some days’ rest they are decanted very carefully, with as little shaking as possible, until not more than one or two cubic centimetres (about a tea-spoonful) of the liquid remains at the bottom. The bottles are then shaken vigorously, with the object of collecting the whole of the deposit from the bottom and the sides into this small quantity of liquid; a drop of this is then examined under the microscope.

Footnote 18:

Since the publication of the author’s “Studies on the Diseases of Wine, and the Dangers resulting to Wine and Beer from the Microscopic Parasites found therein,” some intelligent brewers have derived considerable profit from the application of the theories laid down in that work.

Footnote 19:

If we put a handful of germinating barley from a maltster’s cistern into a little water, and examine drops of the liquid, after it has become turbid, under a microscope, we shall be amazed at the wonderful number of strange microscopic organisms that swarm on the surface of the grains and on the sides of the cistern. There is no doubt that their presence is injurious to germination, inasmuch as they absorb much oxygen; moreover, they acidify the grain and cause it to deteriorate.

Footnote 20:

In these experiments the asbestos is only introduced by way of extra precaution. Originally, in his early experiments in connection with the subject of spontaneous generation, the results of which were published in 1860-62, the author did not use it, and he observed no ill effects resulting from the omission; now, however, he constantly makes use of it. In studies of this kind novel precautions are never thrown away; moreover, the presence of this asbestos is a sure bar to the entrance of insects. The author has preserved for a long time a flask, in the slender neck of which an insect is contained; he killed it with a flame just as it was approaching the liquid. Quite recently, M. Calmettes, a young engineer from the École Centrale, when engaged, at Tantonville, in Tourtel’s brewery, in carrying out certain practical experiments in connection with the process that will he described in one of the later chapters of this work, wrote complaining that his flasks had been suddenly invaded by a swarm of aphides, scarcely larger than phylloxeras, and that many of them had even penetrated into the inside of the curved tubes.