Cookery. The art of cookery, like other arts and handicrafts, is one which cannot be taught in an encyclopædia article, but the general principles which underlie the operations of cookery may be briefly expounded. This part of the subject—the chemistry and physics of cookery—has been much neglected until very lately.
The chief agent in cookery is heat, and therefore a large part of our subject is the consideration of the chemical and physical changes which occur in food materials when subjected to the agency of heat. We may apply this agent either by bringing the food into direct contact with the source of heat, or by exposing it to radiations from the source of heat. Roasting, toasting, grilling, and to a partial extent, baking, are examples of the latter; while stewing, frying, and the so-called 'boiling' of food—i.e. immersion in hot water—are examples of heating by contact. The term 'boiling' is commonly misapplied in a manner that leads to confusion of ideas. Thus we speak of boiling a leg of mutton, boiling fish, boiling potatoes, &c. quite improperly. The food in question is not boiled, should not be boiled; it is merely immersed in water, which is conveniently used as a heating agent. As will presently be shown, even the water itself should not in most cases boil. Frying, properly conducted, is another example. Here a bath of fat is used to convey the heat.
What are the changes effected on the food by the action of cookery? is the fundamental question to be answered in treating cookery as a branch of applied science. What is the difference between a raw and a cooked potato? What is the difference between a raw and a cooked leg of mutton? and other such questions throughout. We all know the difference in flavour, but the chemical and mechanical changes are but little understood. To answer these questions we must first know something of the composition of the uncooked viands.
For this purpose the old-fashioned division of the elements of organic substances into proximate and ultimate is very convenient. The ultimate elements—carbon, oxygen, nitrogen, hydrogen, &c.—are not cookable, and in their uncombined state do not concern our subject; but the proximate elements, or more properly proximate constituents, such as albumen, gelatin, starch, cellulose, &c., are altered, and the whole subject will be best understood by considering separately the alterations which occur to these in the course of cookery.
Taking first the constituents of vegetable food, the largest of these is the material of the cell walls of the vegetable, cellulose, or woody fibre. The next in quantity, as existing in ordinary articles of food, is starch, or fecula, or farina. Both of these are carbohydrates—i.e. compounds of carbon with water, or the elements of water, and they contain these elements in the same proportions, but their structure and digestibility are very different. Starch in its raw state consists of small granules (see STARCH) which, placed in cold water, sink to the bottom without any degree of solution or other change by union with the water. In this condition they are practically indigestible in the human stomach, but when cooked, starch is the most easily digestible of all human food.
The changes that take place in the cookery of starch are considerable. If pure starch (arrow-root is such) be placed in water raised to the temperature of 140° F., the granules swell considerably, and the mixture becomes pasty or viscous. A little stirring breaks up the distended granules, and we obtain a glairy paste such as used by the laundress, and seen in cooked arrow-root. If the heat be now raised from 140° to the boiling-point, and the boiling continued, the gelid mass becomes thicker and thicker; and if there are more than 50 parts of water to 1 of starch, a separation takes place, the starch settling down with its 50 parts of water, and the excess of clear water standing above. We have here a case of hydration or combination with water as the result of cookery, and the probable cause of the improved digestibility. Dry starch may be raised to 300° without becoming thus semi-soluble.
The hydrate once formed may be dried by evaporation, and still retains some water and the same degree of solubility. Many farinaceous preparations, such as corn-flour, &c., consist chiefly of starch in this condition. This, however, is not the limit of starch cookery. If it is heated to about 400°, it is converted into dextrin, which is completely soluble in water at all temperatures, the solution being mucilaginous but not pasty. Dextrin differs from starch in other properties (see DEXTRIN), but is composed of the same elements in the same proportions, —i.e. six equivalents of carbon to five of water, or its elements. This change of starch into dextrin is of great practical importance as an operation of cookery, inasmuch as it anticipates the first stage of the digestion of starch.
The saliva, the pancreatic juice, and one of the intestinal secretions contain a peculiar principle which has received the name of animal diastase, from its resemblance to the diastase of malt. This converts the starch of food into the completely soluble dextrin, a change absolutely necessary for its assimilation as nutriment. In some animals the supply of this is so small that starch is almost worthless to them as food. It passes through the body unaltered. Such is the case with the carnivora. Human infants, when suddenly deprived of their mother's milk, have not sufficiently developed the power of salivary, pancreatic, and intestinal secretion of diastase to digest starch, and therefore demand assistance. Such assistance may be afforded by carrying the cookery of starch to what we venture to call the second stage—viz. its complete or partial conversion into dextrin. Thus, ordinary flour or oatmeal, simply heated in boiling water or milk, is merely subjected to the first stage—viz. hydration of the starch; but if the flour or oatmeal be well baked, a considerable proportion of its starch is converted into dextrin. A knowledge of this is of great importance to mothers, and also to nurses preparing food for dyspeptics, as adults vary greatly in their powers of diastatic secretion.
The reader will now understand why bread is rendered more digestible by toasting, and why crust of bread is more digestible than the crumb, in spite of greater hardness. In the ordinary baking of bread a variable amount of the starch is converted into dextrin. Well-baked bread is more digestible than under-baked. In the cookery of oatcakes, bannocks, scones, and all kinds of biscuits, this should be understood. The writer enjoys the luxury of hot rolls without their indigestibility, by simply moistening stale crusts of bread and reheating them in a kitchen oven. They thus become softened like new bread, and more digestible than before on account of the dextrinisation of a larger proportion of the starch. Baked and fried potatoes have a similar advantage.
The diastase of malt (see MALT) may be used for the dextrinisation of farinaceous food by adding malt flour or extract of malt to it; or the grain itself may be malted. The temperature at which malt diastase acts most vigorously is about 140°. At lower temperatures it acts more slowly; at much higher, its curious property is destroyed. To illustrate its action, make some oatmeal porridge very thick, then add about th part of dry malt flour at about 140°, and stir. In a few minutes the thick pudding becomes quite sloppy owing to the greater solubility of the dextrin into which the starch has thus been converted.
The cellulose—i.e. the stalks and the cell walls, such as the fleshy part of leaves, &c.—are more or less digestible, according to their looseness of structure and their interfluidity or succulent character. Thus we may digest a raw lettuce more easily than a raw cabbage, or the inner leaves of either more readily than the outer leaves or stalks. The action of cookery on cellulose appears to consist in the loosening of its fibres, and rendering them more soluble. It is therefore advantageous that the water in which green vegetables, such as cabbages, are cooked should boil vigorously, the agitation of the steam bubbles assisting in the loosening of the fibres. Cellulose, like starch, may be converted into dextrin and sugar by the combined action of moderate heat with moisture and an acid. This change is aided by a little diastase. Sawdust and old rags may thus be converted into digestible and nutritious food, but not with commercial profit at present. An example of such conversion in Nature's laboratory is afforded by the ripening of a pear. Many varieties which are hard, woody, and sour when full grown in autumn, become gradually softer and sweeter, and finally delicious by simple storage. The action of ensilage (see ENSILAGE) of cattle food probably includes some degree of such conversion of cellulose.
The nitrogenous constituent of grain, the gluten, is not so greatly altered by cookery. The writer's investigations of this neglected subject lead him to the conclusion that the alteration which does occur is that of a partial hydration rendering the gluten more soluble, but this hydration is not so decided and definite as in the case of starch. There is one constituent of vegetable food which demands no cookery. This is pectin (otherwise pectose and pectin)—i.e. vegetable jelly. It exists most abundantly in fruits, and is familiar to all in the form of currant jelly, apple jelly, &c., which are pectin plus sugar. The cookery of vegetable casein will be discussed with that of the casein of milk.
Of the proximate elements of animal food the most abundant is gelatin; it constitutes about half the weight of the body of most animals. It exists in two forms—soluble and insoluble. Its cookery consists in the hydration of the insoluble form and rendering it soluble, as in the steving of bones, tendons, skin, &c. in a stock-pot until their gelatin becomes soluble jelly. The muscular fibre itself, which with its enveloping membranes form lean meat, is subjected to a similar change, but less completely, in the course of cookery.
The cookery of albumen differs materially from any of the preceding. Albumen exists in raw flesh meat as one of its juices, being a glairy liquid which is distributed between the muscular fibres and the joints, and around the bones, forming a lubricant, and probably conveying material of growth and renewal. It is typically seen in the white of eggs. When heated to about 134°, white fibres begin to appear within it. If the heat is continued, and gradually increased, they increase, until at about 160° the whole mass becomes white and nearly opaque. It is now coagulated into a tender, delicate, jelly-like substance, easily digestible and highly nutritious. If the heat is further raised, it becomes harder and harder, up to 212°. If this heat is continued, it shrinks, and becomes tough and horny, losing some of its water of composition, and its easy digestibility.
Ignorance of these particulars, and further ignorance of the fact that water has the same temperature, whether 'simmering' or boiling violently, causes the spoiling of vast quantities of food and wasting of much fuel in this country. The cooking temperature for all animal food is from 160° to 180°. When maintained for any length of time at the temperature of boiling or 'simmering' water, it is spoiled. To prove this, take a beefsteak and cut it in half. Place one half in water in a common saucepan, and boil or 'simmer' it for half an hour or more. Place the other half in water in an open-mouthed jar (such as a gallipot), and place the jar in a saucepan of water so that only the outer water shall boil; cook it thus, and compare with the first. At a continued temperature of not only does the albumen become toughened, but the gelatin also becomes dehydrated, hardened, and indigestible. All stewing operations should, therefore, be conducted at or below the boiling-point. When the exposure to a higher temperature is but for a short period, little or no mischief is done. This is the case in frying and grilling of animal food. These operations should always be rapidly conducted.
Besides the above-named constituents of animal and vegetable food, there are the saline juices necessary for supplying the saline constituents of the blood, and upon which the flavour of food largely depends. These are not altered by cookery, but are too frequently sacrificed. Potatoes, for example, contain a certain proportion of potash salts. The writer has examined the water in which potatoes have been cooked and that which is condensed when they are steamed, and finds that if the potatoes are peeled, a large proportion of the salts pass into the water. If they are cooked 'in their jackets,' much less is lost; but when baked or fried, all is retained. The complete retention of the juices is one of the reasons why roasted and grilled meat has more flavour than that which is cooked in water.
The changes which cookery effects on fat appear to consist in partial dissociation of its proximate elements. It is composed of a fatty acid combined with glycerine. These are partially separated by heat.
Another constituent of both animal and vegetable food is casein. It does not exist in the flesh of animals, but is an important component of milk; is the solid basis of the curd which is separated by the action of rennet or acids (see CASEIN). It also exists in peas, beans, and other seeds of leguminous plants. It is highly nutritious. There are two forms of casein—the soluble and insoluble. It is soluble as it exists in milk, but insoluble after precipitation by acids or rennet, as in making cheese. An infant that digests the casein of milk cannot digest it after separation as cheese.
The writer has succeeded in partially re-converting the insoluble to the soluble form by adding bicarbonate of potash in the proportion of th to d of an ounce to 1 lb. of cheese; the potash dissolved in about a teacupful of water, and the cheese, grated or sliced, added to the solution, which is boiled until the cheese dissolves, forming a custard-like result. This may be added to oatmeal porridge and a multitude of other preparations. The theory upon which this method of treating cheese was founded is, that the curdling of milk is due to the combination of an acid with the natural alkali of the soluble casein, chiefly consisting of potash. The artificial addition in the proportion named not only renders the cheese more digestible, but restores the saline constituent of the original milk, which in the course of cheese-making, passed into the whey. The importance of thus rendering cheese more digestible, and supplying its saline dietetic deficiency, will be understood by the fact that 20 lb. of cheese contain as much nutriment as a sheep weighing more than 60 lb. Lean beef and mutton contain from to per cent. of water, cheese about 30 per cent. and no bone. Cheese may be stored and carried almost as easily as coal.
A multitude of cookery books exist, too many to name. These consist mainly of instructions in the preparation of particular dishes. The philosophy of cookery has a very limited literature. In the third, sixth, and tenth essays of Benjamin Thompson, Count Rumford (1796), The Chemis- try of Cookery, by W. Mattieu Williams (1885), and Cantor Lectures on The Scientific Basis of Cookery, by the same author, the subject is treated as a branch of applied science. Count Rumford's essays also include his remarkable achievements in economic feeding of the poor in Munich, and his improvements of cooking apparatus. Of late, much more attention has been bestowed on cookery in Great Britain, and the board-schools in the principal towns now make provision for instructing their girl pupils in this important subject. The processes of roasting, stewing, &c. will be treated under their respective titles. See also DIET, DIGESTION, and the articles on BRILLAT-SAVARIN and SOYER.