The preservation of food materials may be considered from two points of view: (1) the holding in good condition for a sufficient length of time the current supply of food, and (2) the preservation for an indefinite period of such food products as canned goods and preserves.

Food preservation as a whole involves many methods and devices. It is not intended to discuss these in detail, but rather to set forth the principles that are generally applicable to the maintenance of food materials in a sound condition.

329. Factors Involved

A fundamental and main factor in causing undesirable changes in food is the presence and activity of micro-organisms such as the molds and many types of bacteria. The conditions related to the control of these minute and ever present organisms are cleanliness, moisture, temperature, heat, sunlight, various disinfectants, and preservatives. It is not proposed to treat each of these conditions or factors separately, but to show their relation to different classes of food materials.

330. Moist Foods

Many foods, such as milk, meats, certain kinds of pastry, puddings, and similar cooked preparations, and breads and cakes that are stored in a closed space to prevent evaporation, necessarily contain an amount of water that is favorable to the inroads of the low forms of life. With such foods two conditions determine the success with which they are held against fungus or bacterial action, viz., cleanliness and temperature. The receptacle of whatever kind in which moist foods are kept should be scrupulously clean, that is, no accumulation of dirt, however small, should be permitted as a breeding place for germ life. This is fundamental. The refrigerator is often neglected and does not receive the frequent thorough cleaning that is necessary to the best conditions. Jars, cake boxes and other receptacles in which bread and cake are stored, should receive no less careful attention. A low temperature is a safeguard against the growth of micro-organisms. In a refrigerator where meat and other perishable articles are kept the ice supply should be sufficient to hold the temperature down to 40° F. or less. This means a larger ice box in proportion to the rest of the space than is found in some refrigerators.

Jars or boxes in which bread and cake are kept should be located in as cool a place as possible.

331. Dry Foods

These are principally flours, meals, sugar, dried and preserved meats, and dried fruits. Some of these are immune to the action of germ life because of the presence of some substance like salt or sugar in sufficient concentration to act as a germicide. This may be true of preserved meats. The flours, meals, and dried fruits maintain a sound condition unless through dampness they absorb moisture beyond a safe proportion. Such materials should be kept in a dry place, well lighted and well ventilated, if possible. Fresh air and sunlight, even diffused light, are inimical to bacteria and similar organisms. Dark and unventilated storerooms are not desirable.