9. Each one of the phases of cookery has its importance, but if success is to be achieved in this art, careful attention must be given to the selection of what is to be cooked, so as to determine its value and suitability. To insure the best selection, therefore, the housewife should decide whether the food material she purchases will fit the needs of the persons who are to eat it; whether the amount of labor involved in the preparation will be too great in proportion to the results obtained; whether the loss in preparation, that is, the proportion of refuse to edible matter, will be sufficient to affect the cost materially; what the approximate loss in cooking will be; whether the food will serve to the best advantage after it is cooked; and, finally, whether or not all who are to eat it will like it. The market price also is a factor that cannot be disregarded, for, as has been explained, it is important to keep within the limits of the amount that may be spent and at the same time provide the right kind of nourishment for each member of the family.
10. In order to select food material that will meet the requirements just set forth, three important matters must be considered; namely, the substances of which it is composed; its measure of energy-producing material, or what is called its food, or fuel, value; and its digestion and absorption. Until these are understood, the actual cost of any article of food cannot be properly determined, although its price at all times may be known.
However, before a study of any of these matters is entered into, it is necessary to know just what is meant by food and what food does for the body. As is well understood, the body requires material by which it may be built and its tissues repaired when they are torn down by work and exercise. In addition it requires a supply of heat to maintain it at normal temperature and provide it with sufficient energy to do the work required of it. The material that will accomplish these important things is food, which may therefore be regarded as anything that, when taken into the body, will build and repair its tissues or will furnish it with the energy required to do its work.
FOOD SUBSTANCES
11. Although, as has just been stated, food may be considered as anything that the human engine can make over into tissue or use in living and working, not all foods are equally desirable any more than all materials are equally good in the construction of a steam engine and in the production of its working power. Those food substances which are the most wholesome and healthful are the ones to be chosen, but proper choice cannot be made unless the buyer knows of what the particular food consists and what it is expected to do. To aid in the selection of food, therefore, it is extremely necessary to become familiar with the five substances, constituents, or principles of which foods are made up; namely, water, mineral matter, or ash, protein, fat, and carbohydrate. A knowledge of these will help also in determining the cooking methods to adopt, for this depends on the effect that heat has on the various substances present in a food. Of course, so far as flavor is concerned, it is possible for the experienced cook to prepare many dishes successfully without knowing the effect of heat on the different food constituents; but to cook intelligently, with that success which makes for actual economy and digestibility, certain facts must be known concerning the food principles and the effect of dry and moist heat on foods.
12. WATER.--Of the various constituents that are found in the human body, water occurs in the largest quantity. As a food substance, it is an extremely important feature of a person's diet. Its chief purpose is to replenish the liquids of the body and to assist in the digestion of food. Although nature provides considerable amounts of water in most foods, large quantities must be taken in the diet as a beverage. In fact, it is the need of the body for water that has led to the development of numerous beverages. Besides being necessary in building up the body and keeping it in a healthy condition, water has a special function to perform in cooking, as is explained later. Although this food substance is extremely essential to life, it is seldom considered in the selection of food, because, as has just been mentioned, nearly all foods contain water.
13. MINERAL MATTER.--Ranking next to water in the quantity contained in the human body is mineral matter. This constituent, which is also called ash or mineral salts, forms the main part of the body's framework, or skeleton. In the building and maintaining of the body, mineral salts serve three purposes--to give rigidity and permanence to the skeleton, to form an essential element of active tissue, and to provide the required alkalinity or acidity for the digestive juices and other secretions.
The origin and distribution of these mineral substances are of interest. Plants in their growth seize from the earth the salts of minerals and combine them with other substances that make up their living tissue. Then human beings, as well as other living creatures, get their supply of these needed salts from the plants that they take as food, this being the only form in which the salts can be thoroughly assimilated. These salts are not affected by cooking unless some process is used that removes such of them as are readily soluble in water. When this occurs, the result is usually waste, as, for instance, where no use is made of the water in which some vegetables are boiled. As is true of water, mineral matter, even though it is found in large quantities in the body, is usually disregarded when food is purchased. This is due to the fact that this important nutritive material appears in some form in nearly all foods and therefore does not necessitate the housewife's stopping to question its presence.
14. PROTEIN.--The food substance known as protein is a very important factor in the growth and repair of the body; in fact, these processes cannot be carried on unless protein is present in the diet. However, while a certain quantity of protein is essential, the amount is not very large and more than is required is likely to be harmful, or, since the body can make no use of it, to be at least waste material. The principal sources of protein are lean meat, eggs, milk, certain grains, nuts, and the legumes, which include such foods as beans and peas. Because of the ease with which they are digested, meat, fish, eggs, and milk are more valuable sources of protein than bread, beans, and nuts. However, as the foods that are most valuable for proteins cost more than others, a mixed diet is necessary if only a limited amount of money with which to purchase foods is available.