Action of Heat.—The most important results of cookery are to be ascribed to the action of heat upon the various constituents of our food. Many foods that we now eat would become useless to mankind if we had to eat them raw. Cooking may not always alter the chemical constitution of a food, but even then it may entirely change its practical value to mankind. As a matter of fact, however, heat does alter the chemical nature of a great many foods to a considerable extent. Still, even if the change may be nothing that chemical analysis can detect, yet it is perceptible to every one who eats a dinner.
There is no greater mistake than to suppose that the chemical analysis of a food tells us its value. Flesh and bones, and fat and heat can be, by some warm-blooded animals, obtained from a diet of grass or woody fibre, but we should starve in the midst of such plenty.
Many of the changes wrought by heat are easily explained. Whether albumen is barely coagulated or is hard and horny, whether fibre is shrivelled or swelled, whether gelatine is dry and brittle or dissolved it does not take a scientific head to discover. But science tells us why these things are, and so enables us to bring our food readily into whatever state we will.
Given certain food, one cook so manipulates it that the consumer is well nourished and pleased; another cook leaves him hungry and discontented.
Combination of Foods.—In preparing food we must remember also to combine all necessary foods in a right proportion. Some foods are deficient in one respect, some superabundant in another: a little addition here and there helps digestion and supplies the body with what it needs. All cooks do this in obedience to the natural promptings of the appetite. To rice, rich in starch, they add butter and cream; with peas, they serve fat bacon; salt-fish has less nourishment than its egg sauce; beef steak is balanced by boiled potatoes. But the customs of the kitchen often err, and we have much to learn that our artificially stimulated appetites fail to teach.
Not only is the deficient supplied, but the indigestible is removed. Bran from flour, paring from potatoes, cellulose from vegetables go to feed animals whose digestions are stronger than ours, and who utilise our discarded food to produce other in a form more fitted to our powers.
Another service that cookery does is to economize our food by heating it. Part of what we eat is used as fuel or heat-giving food—is burnt or oxidized, to keep the heat of the body at a certain point. Wherever we live and whatever we do, as long as we are in health our body temperature is always 98° Fahr. neither more nor less. When we take cold food some of the heat of the body has to be used to heat it, for the same reason that when we put fresh coals on the fire the temperature of the room is lowered for a time. So we take our food warm and use coals to do what our food must otherwise do. There