Conditions under which different foods retain desirable quality indicate the necessities in preserving them. Preservation of food is such treatment of it as will keep it in suitable condition for human use. Green vegetables even in season are perishable. Prompt use is therefore the essential precaution against their deterioration.

Plants are living until they decay. They need the conditions of life, as air to breathe, though after they are plucked they need no longer the requirements for growth, as food. For seasonal use low temperature, complete cleanliness of receptacles and atmosphere, including protection from dust, are usually adequate attention in markets, shops, homes.

"Green vegetables lose freshness, and wilt. Some lose sweetness; (fresh corn and peas do. Since they need to be kept in cool, dry air, they should be in a clean, wholesome, well-ventilated cellar or refrigerator. Slightly wilted vegetables revive by standing in water, but this may dissolve out their salts, also some protein and sugar. Lettuce wrapped in a moistened cloth and placed on ice remains crisp. If leaves discolor, remove at once. Vegetables should not be washed until they are to be used, as such moisture may hasten decay or mold-growth.

Starchy vegetables, such as potatoes and beets, need to be kept where it is cool and dry, and with little air in actual contact with them. They therefore keep well piled in cool, dark bins. The air of the room should, however, be fresh. Freezing and thawing changes vegetable-composition and should be avoided. Sprouting too renders a vegetable undesirable for food. The regulation of moisture, light, temperature, is important because the degrees of these affect differently the growth of the various bacteria as well as the natural processes of decay in the plant itself.