Culinary Chemistry / The Scientific Principles of Cookery, with Concise Instructions for Preparing Good and Wholesome Pickles, Vinegar, Conserves, Fruit Jellies, Marmalades, and Various Other Alimentary Substances Employed in Domestic Economy, with Observations on the Chemical Constitution and Nutritive Qualities of Different Kinds of Food.

by Friedrich Christian Accum

COMPARISON OF THE CHEMICAL CHANGES PRODUCED ON ANIMAL AND VEGETABLE FOOD, IN THE DIFFERENT PROCESSES OF COOKERY.

The principal operations of cookery which we have just examined and explained, all agree in this, that they effect some chemical change on the materials operated upon, by which they are rendered more digestible, more wholesome, and consequently more nutritive.

In such of the operations as are performed by the direct application of heat to the flesh of animals, namely, roasting, baking, frying, and broiling, the meat loses the vapid and nauseous taste and odour which it possesses in a raw state, and becomes savoury, juicy, and grateful to the taste. These effects arise from the development of the gelatine and osmazome from the smaller vessels, and their being rendered soluble; while, at the same time a portion of the fat is liquified, and combines with them after they are disengaged.

The fibres again, on the surface of the meat, are partly scorched, and form a crust, which, except in the interstices of the corrugations, is impermeable, and consequently prevents the savoury gravy that is disengaged from the fibres from oozing out or becoming evaporated. It is thus only disengaged from its chemical union with the fibres, and remains mechanically united with them in the meat, after it is cooked, as we see upon cutting into the fibrous portion.

The effect produced on the fat is somewhat different. The direct application of fire to this portion of the meat soon melts part of the substance, and raises it to the boiling point, or nearly so; the water which it contains is consequently given off in the form of steam, and it carries with it a quantity of osmazome. It is this which occasions the peculiar odour that arises from meat while roasting.

The vapid taste is also corrected by the empyreuma, combined with a minute quantity of ammonia, which is soon developed on the surface of the fat, by the partial charring—not of the fat itself, but of the cellular membrane in which it is enveloped. This structure may easily be perceived on a slight examination of a piece of recent fat; all the membranous or skinny portions being only the receptacles or nests for the fat itself. And since these membranes are for the most part exceedingly thin and easily ruptured, and since heat increases the volume of the fat which they contain, the application of heat in roasting or broiling will soon make all the membranes burst which are within its influence, and thus give a free passage for the juices to unite with each other.

There is, according to these statements, but little loss of the substance of meat when roasted or broiled, and the chemical changes produced are so slight, that nearly all its nutritive elements must be preserved and concentrated in the cooked meat.

When there is a watery medium used, through which heat is applied to animal food, as for example, in the process of stewing or boiling, a portion of the fat, gelatine, and osmazome, is dissolved, and mixes with the water. Nutritive matter is consequently lost, or, at least, it is transferred from the meat to the broth or soup.

In the operation of stewing there is less of this transfer made; and, besides, as the medium is scarcely kept at a boiling heat, less of the nutritive juices are dissolved. When, however, the broth or gravy in which meat is boiled is made use of, as well as the meat itself, boiling is the most economical practice; for though nothing be added except the water, this itself, if it contains no nourishment, at least fills the stomach, and serves to diffuse more widely the nutritive juices of the meat which it holds in solution or in mixture.

But though boiling be thus the most economical practice, it is not always to the taste of individuals, or even of whole nations to use the broth or soup. The English and Irish, for example, rarely follow this practice, while the Scots, French, and Germans, prefer it to all other modes of cooking. In general, then, it should seem, that roasting as it is the simplest, is also the best mode of rendering the flesh of animals fit for human food. Roasted meat is wholesome and highly nourishing; and when there is not too much of the empyreumatic crust formed, it is for the most part easily digested. In these respects, broiled meat differs little from such as is roasted. What is fried is always less tender. It is often found that roasted or broiled meat sits more easily on the stomach, and is sooner digested by those whose digestive organs are feeble or diseased, than fried or boiled meat, or broths and stews.

The effects of the processes of cookery on vegetable substances, though usually very slight and simple, are in some instances both striking and unexpected. For example, some sorts of vegetables are extremely acrid and even poisonous in their crude state, and altogether unfit for human food; yet, by simply boiling them in water, they become bland, sweet, and wholesome. Several species of arum (cuckoo-pint), which are very acrid, and would be dangerous to use raw, become quite palatable pot-herbs when boiled. Their acrimony must reside in a very volatile principle, which, during the boiling, makes its escape, or is chemically altered; but the nature of this principle has not yet been accurately investigated by chemists. A more familiar example than this is found in onions, leeks, and garlick, whose acrimony and strong odour can be almost destroyed, or rather driven off by a sufficiently long application of heat, either directly, or through the medium of water. Many other instances could be given, but we shall content ourselves with one more.

Every body knows that potatoes, in a raw state, are nauseous and unpalatable. It is not, perhaps, so generally known that the potatoe, (solanum tuberosum,) belongs to the night-shade genus of plants, which are all more or less poisonous. If potatoes were used raw, in any quantity, they would be deleterious to man; nor does it disprove this that cattle eat them with impunity, as sheep and goats eat plants much more strongly poisonous to man, such as hemlockdropwort, [oenanthe crocata;] and waterhemlock, [phelandrium aquaticum].

By boiling or roasting, however, all the unpalatable and all the unwholesome qualities of the potatoe are changed, and it becomes farinaceous, wholesome, digestible, and highly nutritious. Yet, although this change is remarkable, and could scarcely have been anticipated, very little is lost and nothing is added to the potatoe by either roasting or boiling, yet its immediate constituent parts have evidently suffered a very great chemical alteration, chiefly, in consequence it should seem, from the farinaceous substance being acted on by water.

Vegetables, when used as food, are most commonly boiled, and seldom baked or roasted. Salads, indeed, are eaten raw, without any application of heat. The chemical action of heat on pot-herbs, on esculent roots, and leguminous seeds, does not appear to be confined to the mere softening of their fibres, or to the solution or coagulation of some of their juices and component parts; for we have just now seen that their flavour, and other sensible qualities, as well as their texture, suffer a remarkable chemical change, which greatly improves their alimentary properties.

In the cooking of vegetables, saccharine matter is often formed, or mucilage and jelly extracted; and the whole substance is on that account rendered more palatable, wholesome, and nourishing. These effects are very well exemplified in the changes which take place in flour when converted into bread;[24] which differs materially from flour paste, insomuch that the constituent parts of the unbaked dough can no longer be separated by the processes employed in chemical analysis.

[24] A treatise on the art of making good and wholesome bread of wheat, oats, rye, barley, and other farinaceous grain, exhibiting the alimentary properties and chemical constitution of different kinds of bread corn, and of the various substitutes used for bread, in different parts of the world, p. 58, 1821.

Vegetable substances are most commonly boiled or baked; or, if occasionly fried or roasted, there is always much water present, which prevents the greater action of the fire from penetrating below the surface. The universal effect of cookery by boiling upon vegetable substances, is to dissolve in the water some of their constituents, such as the mucilage and starch, and to render those that are not properly soluble, as the gluten and fibre, softer and more pulpy.