CHAPTER VI.

THE PREPARATION AND PRESERVATION OF FOOD.

OBJECTS OF COOKING.—Food may be taken in its crude condition, as directly derived from the animal or vegetable world, or after it has undergone a preparatory process of cooking. Man is the only animal who cooks his food. Many foods, in the uncooked condition are almost entirely incapable of digestion by him—such as the proteid and farinaceous materials contained in the seeds of cereal and leguminous plants. But cooking, as a preparatory help to the digestion of food, is not equally required by all foods. Thus, fruit is commonly taken uncooked, and does not undergo any important alteration on cooking. Salads are taken uncooked, but not for their nutritive properties so much as for a relish to other foods, and for their quasi-medicinal properties. Milk, again, may be taken cooked or uncooked. The oyster is the only animal which is eaten habitually, and by preference, in the uncooked condition; and there is a physiological reason for this universal custom. The large fawn-coloured liver, which constitutes the delicacy of the oyster, is little else than glycogen, associated with its appropriate ferment diastase, so that the oyster is almost self-digestive. When cooked, the ferment is destroyed, and digestion of the oyster becomes more difficult.

Cooking is intended—1. _To make the food softer_, and in part to mechanically disintegrate it, thus rendering it more easily masticated and digested. In fact, cooking, in the best sense, is an artificial help to digestion; and digestion may well be said to commence in the kitchen.

2. _To produce certain chemical changes._ Thus, starch is partially converted into dextrine; gelatin is formed from connective tissue, etc.

3. _To destroy any noxious parasites_ present in the food, or obviate any ill effects from _putrefactive changes_. Diseased meat chiefly produces bad effects when imperfectly cooked.

4. _To make the food more pleasant_ to the eye and agreeable to the palate. The improved savour in cooked meat, for instance, has a very appetising effect, and consequently makes digestion easier.

THE COOKING OF FLESH.—1. =Roasting= is, perhaps, the most perfect way of cooking meat. It exalts its flavour more than any other method. In roasting, place the meat at first sufficiently near a brisk fire, so that the albumin on its surface may be readily coagulated, and the juices retained in the interior of the joint. After about fifteen minutes, the joint ought to be removed somewhat further from the fire, and allowed to cook slowly. Frequent basting is desirable to obtain a good result. Brown meats, such as beef, mutton, and goose, require a quarter of an hour per pound weight; veal and pork require about ten minutes additional, to ensure the absence of redness. White-fleshed birds require a somewhat shorter time. The time required in roasting will be a little more if the joint is large, or the fire not very clear. To ascertain if the meat is sufficiently cooked, press the fleshy part; if it remains depressed, it is done; if not done, it retains its elasticity. At the first incision, gravy should flow out of a reddish colour.

_The changes undergone_ during roasting are, that the connective tissues uniting the muscular fibres is converted by the gradual heat into gelatin, which is soluble and easily digested; the muscular fibres, consequently, become more separable, and the myosin of which they consist is rendered more digestible. The fat is partly melted out of its fat cells, and partly combines with the alkali from the blood-serum. Empyreumatic oils (_i.e._ fat partially burnt), developed by charring of the surface of the joint, are carried off when it is roasted in front of the fire; and so, to a large extent, is acrolein. Acrolein (C₃H₄O) is always produced by the destructive distillation of neutral fats containing glycerine, and is the cause of the intolerably pungent odour accompanying the process. Osmazome, a peculiar extractive matter, on which the flavour and odour of meat depend, is developed better by roasting than by any other method of cooking.

It is useful to remember, in buying beef or mutton, that 20 per cent. must be allowed for bone and 20 to 30 per cent. for the loss during cooking.

The following figures are by Johnston:

IN ROASTING. IN BAKING. IN BOILING. 4 lb. of mutton lose in weight 1 lb. 6 oz. 1 lb. 4 oz. 14 oz. „ beef „ „ 1 lb. 5 oz. 1 lb. 3 oz. 1 lb.

Thus roasting is the least economical method of cooking. The chief loss, however, is of water; the dripping and gravy are recoverable.

2. =Baking= of meat in a closed oven does not produce so agreeable a result as roasting in front of an open fire. The oven ought always to be very hot before the meat is put in, in order to rapidly coagulate its surface. Baked meat may have an unpleasant flavour, owing to its saturation with empyreumatic oils, which escape in open roasting. The unpleasant flavour can be prevented by covering the meat with a layer of some non-conducting material, as a pie-dish or a crust, no empyreuma being then formed. Baked white of egg, as in the dish of fried ham and eggs, is one of the most indigestible forms of albumin obtainable.

3. =Boiling= of meat requires the same time as roasting. If the flavour and juices are to be retained, the joint ought first to be plunged into soft boiling water, and then, after three minutes, allowed to stand aside in water at 170° Fahr. The preliminary boiling forms a coating of coagulated albumin over the joint. Where there is no thermometer to guide the cooking—after the preliminary boiling for three to five minutes, add three pints of cold water to each gallon of boiling water, and retain at the same temperature for the rest of the process, _i.e._, at about 170° Fahr. If the meat is boiled in an inner vessel surrounded by water (water-bath), the temperature of the inner vessel does not rise above 160°-170° F. Ordinary “simmering” means that the meat is kept all the time at a temperature of 212° F. and is thus spoilt. The boiling of an egg is an example of the same point. If an egg is kept in water at a temperature of 170° F. for 10 to 15 minutes, its contents form a tender jelly, while an egg kept in water at 212° F. for the same length of time is hard and tough. An egg is more digestible when cooked in water at 170° F. for 10 minutes than when boiled in water for 2½ minutes.

The use of soft water for cooking purposes is always advisable; otherwise a longer period must be allowed. A preliminary boiling for a few minutes renders hard water softer, and the addition of a little carbonate of soda has a like effect.

When meat is inserted in water at a temperature below its boiling point, the juices are gradually extracted, while the meat is left a mass of indigestible fibres. A good soup is produced, but the meat is almost valueless. In order that the soups and broths may be nutritious, the less heat is employed in their preparation the better. If a soup is strained to make it clear, much of the most valuable part is removed.

=Stewing= is a process intermediate between boiling and baking. It possesses the great advantage over dry baking that no empyreumatic gases are produced, and there is no charring. The temperature of the stew-pan ought never to be above 180° Fahr.; at this heat the roughest and coarsest kinds of meat are made tender. The only objection to stewing is that the meat becomes saturated with fat and gravy, and is too rich for weak stomachs. It is advisable to stew lean meats only.

=Hashing= is a process of stewing applied to meat which has been previously cooked. The consequence of this double cooking, is that the meat becomes tough and leathery. A modified hash in which the meat is simply well warmed throughout is preferable.

=Frying=, unless carefully done, renders meat difficult of digestion, each fibre becoming coated with fat. The art is to “fry lightly,” that is, to burn quickly and evenly, so that no charring is produced. Two methods of frying are described. In the first, the substance to be fried, as an omelette or pancake, is placed with a little fat or oil in a frying-pan. This is really a modified process of roasting, the fat merely serving to prevent the object from adhering to the shallow pan. In the second, the substance to be fried is immersed in fat; for this purpose a frying kettle is required. Olive oil or good cotton seed oil is best for use in the frying-kettle. Lard is a bad material for frying; both it and butter are apt to burn unless heated slowly. Dripping is a good substance for frying. The fat used must be heated to from 350° to 390° F., and then the substance to be fried, _e.g._ a sole, plunged into it and left for two or three minutes. In this process the substance of the sole is really being steamed by the steam generated in the substance of the sole.

6. =Broiling and Grilling= are really processes of roasting applied to small portions of meat. In grilling, it is important that the gridiron should be hot before putting anything on it. An external coagulation of albumin is produced, as in good roasting and boiling.

THE COOKING OF MIXED DISHES.—A few instances may be given of common errors in preparing compound dishes. An egg in a custard, or just coagulated in a poached egg, is a light and easily-digested food; baked half an hour in a pudding, it is much less digestible; fried with ham, it is almost as indigestible as leather. Spices, if mixed with a dish before it is boiled, lose nearly all their flavouring power, while they remain irritating. They ought to be added near the end of the cooking process. A soup containing vegetables, as well as meat juices, should be prepared in two parts. The vegetables require prolonged boiling; gravy is spoilt by this. Similarly, the jam in a tartlet, if inserted before baking, loses its proper fruity flavour; and oysters baked in a beef-steak pie are indigestible.

THE COOKING OF VEGETABLE FOODS.—=Bread= is either vesiculated or unvesiculated; the latter being what is called unleavened bread. Vesiculation of bread has usually been produced by _fermentation_ of some of the sugar of the flour. The starch first becomes sugar (dextrose) and then the growth of the yeast plant in the dough splits this up into alcohol and carbonic acid gas. The carbonic acid percolates the substance of the dough, rendering it porous. When it has “risen” sufficiently, the dough is placed in the oven. The heat of the latter kills the yeast plant, thus preventing any further fermentation, but at the same time expands the carbonic acid gas in the bread, rendering the latter still more porous, and drives off in a gaseous condition the greater part of the alcohol produced by the previous fermentation.

It is objected to this plan of making bread, that a little of the sugar is wasted in producing alcohol and carbonic acid. To remedy this, _another plan_ is sometimes adopted, as first proposed by _Dr. Dauglish_. In it the dough is charged with carbonic acid dissolved in water under considerable pressure. The gas escapes in the substance of the dough, and on baking expands as in the ordinary method of making bread. Bread made in this manner, is called “aerated bread.” Nevill’s bread has a solution of carbonate of ammonia incorporated in the dough, which is dissipated by heat, thus causing vesiculation of the bread.

On the continent, a mixture of hydrochloric acid and carbonate of soda is commonly used, carbonic acid and common salt being formed in the dough. Thus NaHCO₃ + HCl = NaCl + H₂O + CO₂. The hydrochloric acid employed should be perfectly pure and free from arsenic. Baking powders are also largely used for making cakes. “Self-raising” flour is flour with which baking-powder has already been mixed. Most baking-powders consist of a mixture of carbonate of soda and tartaric acid or bitartrate of potash, diluted with starch. When wetted, carbonic acid gas is evolved. A few contain alum, which is now an illegal material for this purpose.

Ten pounds of flour ought to make thirteen to fourteen of bread. The use of stale bread is much more economical than of newly-made bread; besides this, it is more digestible. Newly-made bread is more palatable than stale, but it is more cohesive, and does not crumble into separate particles like stale bread. The consequence is, that it is less digestible, being less easily penetrated by the saliva and other digestive juices. The effect of _toasting_ is to render bread more friable, and consequently more digestible. It ought, however, to be thin and eaten soon after it is made; when thick and kept too long, it becomes tough and leathery.

=Pastry= is less easily digested than ordinary bread. The lard or dripping added renders it more flaky and less easily pulverised; and, in addition, the fat coats over the starch cells; and thus the action of the digestive juices on the pastry is impeded.

=Potatoes= ought to be boiled in their jackets, or steamed, to avoid loss of nitrogenous material and salts. Moist heat causes the starch granules to swell, and ultimately softens and bursts the cellulose envelopes in which these are contained. Dry heat, as when potatoes are baked, converts starch into a soluble form, and ultimately into dextrine (= C₆H₁₀O₅), an intermediate stage towards the formation of dextrose (_i.e._ glucose = C₆H₁₂O₆).

=Peas and Beans= ought to be boiled slowly and for a long time to render them more digestible. If old, they ought to be soaked in cold water for twenty-four hours, then crushed, and stewed. Hard water must be avoided in the cooking of peas and beans as well as of other vegetables, as the lime-salts form insoluble compounds with legumin.

=Green vegetables= require thorough and prolonged cooking. This renders their tissues softer and more easily attacked in digestion. The members of the cabbage tribe and carrots can hardly be boiled too long. Soft water ought always to be used; this is one reason why steaming is preferable. Before boiling, all vegetables should be well washed in cold water. A little vinegar will remove any insects present.

COOKING APPARATUS.—The apparatus required in cooking may be divided into kitchen utensils and cooking ranges.

To ensure good cooking, perfect cleanliness of all apparatus is indispensable. The use of the frying-pan, gridiron, spit, and oven has been sufficiently indicated under the description of the different methods of cooking. The form of stove to be used for cooking meat is gradually being settled against the old open stove. Although this secures a somewhat more savoury joint than when meat is baked, it is extravagant in working. The closed kitchener in which coal is employed is less economical than a gas stove at the present price of gas, if the latter is carefully used.

Various appliances for economising fuel have been devised, and at the same time of allowing of the prolonged action of a moderate degree of heat. These are usually constructed on the principle of an ordinary bath, consisting of a double pan, with a layer of water between the two compartments. Warren’s cooking-pot belongs to this type. The Aladdin oven consists of an iron box with an opening above to let off superfluous steam. This box is surrounded by another composed of non-conducting material, while a lamp below furnishes the heat. Dr. Atkinson has calculated that in an ordinary oven 2 lbs. of fuel must be expended for every pound of food cooked, while in his Aladdin oven 2½ lbs. of fuel will cook 60 lbs. of food. Time is an important element in cooking. Food is most thoroughly cooked and most digestible when subjected to a temperature below that of boiling water for a prolonged period.

THE PRESERVATION OF FOOD.—All organic foods tend rapidly to decompose and putrefy. Putrefaction only occurs when a warm and moist substance is exposed to the air. The problem of preserving any food, therefore, may be solved (1) by keeping it at a very low temperature, (2) by desiccating it, or (3) by boiling or steaming it so as to destroy any microbes in the food which would otherwise start putrefaction, and then fastening it in an air-tight case.

Milk is commonly preserved as condensed milk, and in this condition is very valuable. A pure condensed milk is now supplied, prepared without the addition of sugar or any antiseptic, but in which, as in other condensed milks, all disease-producing or decomposition-producing microbes have been destroyed during the process of concentration. Milk may also be desiccated; in this condition it is difficult of digestion.

In addition to the household methods of preserving fruits, large quantities of fruits—both moist and dry—are now imported, protected by syrup or sugar, in sealed canisters; and they retain the original flavour almost unchanged.

The preservation of meat is effected by—

1. =Drying.=—This must be done rapidly. It is a process which is best applicable to fish, but has been applied also to beef. Dried Hamburg beef is used for making sausages. Pemmican, largely used by Arctic voyagers, consists of a mixture of meat and fat, dried and powdered along with some spices; it is generally eaten with some kind of meal.

2. =Cold.=—Frozen meat now forms a very large part of the food of the English people. If the meat has been frozen before rigor mortis (rigidity after death) has commenced, it keeps well; if frozen later, it rapidly decomposes after being thawed. Freezing arrests putrefaction and tends to conceal its odour. Hence the bad condition of frozen fish may not be detected until it is cooked. In cooking frozen meat, time should be allowed for thawing to occur, before the meat is placed in the oven. Much of the ill-founded prejudice against frozen meat arises from inattention to this point. Frozen meat is equal in nutritive value to and does not lose more in cooking than fresh meat.

3. =Salting= may be done with brine or saltpetre (nitrate of potassium); the latter does not decolourize the meat like the former. Salted meats have lost much of their nutritive material, in the form of albumin and salts, and the remaining meat is harder and more difficult of digestion than fresh meat.

4. =Immersion in antiseptic liquids= or gases, as sulphite of soda, is objectionable, on account of the addition of extraneous, and not altogether innocuous, salts. Boric acid powder is largely used for sprinkling on meat, particularly rabbits, etc., and for preserving hams and other meats. Its use is to be deprecated. All such meats should be thoroughly washed with water, before being cooked.

Solutions of _boric acid and borax_ are frequently added to milk. Their use is objectionable (_a_) because they tend to conceal incipient decomposition, but do not prevent its possible evil effects, and (_b_) because they enable the farmer to palm off dirty milk on the public. Were the addition of preservatives to milk forbidden, the farmer could perfectly well keep his milk sweet until it reached the town-consumer by adopting strict measures of cleanliness, and by cooling his milk before it leaves the farm. At the least it should be made obligatory on the milk retailer to declare the presence of preservatives in milk sold by him.

The presence of borax or boric acid can be detected by evaporating the milk to dryness, incinerating and then moistening the ash with a drop of strong sulphuric acid. If a little alcohol be now added, on applying a light, a green flame indicates boric acid. Milk or cream containing boric acid turns blue litmus paper red.

_Formalin_ is also sometimes used as a preservative for milk in very weak solution.

Its presence can be determined by diluting the milk with water in a test-tube, and running strong sulphuric acid down the side of the tube, taking care to prevent mixing. At the junction of the acid and diluted milk a violet ring is seen if formalin is present.

_Salicylic acid_ was formerly used as a milk preservative, but is now seldom used except in beers. All these preservatives are objectionable in milk, although their injurious action may be difficult to prove.

5. =Coating with fat or gelatine= has only succeeded in conjunction with the exclusion of air. This process is especially applicable to fishes, as tinned sardines. In a modified form, it is useful in coating potted meats, etc.

6. =Heating and Air-tight Cases.=—Tinned meats prepared according to this method are imported in large quantities. In the process of preparation, the cases are packed with meat and filled up with gravy, and then closed with a cover which is hermetically sealed, except at one point. The case is then heated to 250° Fahr., in order to drive out all air, and destroy any putrefactive germs present. The open point is sealed while the gravy is still boiling, thus making the case completely air-tight. Albumin is coagulated at about 170° Fahr.; the higher temperature, which it is found necessary to employ, overcooks the meat and renders it less digestible (see also p. 40).