Refrigeration of food is its preservation by lowering the temperature below that favorable for bacterial growth. Though this temperature varies for different kinds of bacteria, it is generally true that freezing or temperatures near it are un-propitious for bacteria. The disease-producing bacteria that attack persons for food grow best at the temperature of the body (98 2/5° F.). But some of these have spore-forms that resist destruction by anything except extremely high heat continued for some time, or chemicals dangerous to human life. Frozen or refrigerated foods may therefore contain such bacteria in live form, that will develop when taken into the human body. Hence the imperative necessity of keeping foods free from contamination which are to be preserved through freezing or refrigeration. Impure water does not form pure ice.

The bacteria that attack foods for their own food (that is, putrefactive bacteria that cause food-decomposition), though also affected by cold as are the disease-producing (pathogenic) bacteria, are also not assuredly destroyed by cold. Some putrefactive bacteria remain somewhat active at low temperatures and cause food-deterioration during this form of preservation. The refreezing of frozen mixtures, such as ice-creams, or the use of such foods for food-ingredients when melted, as melted ice-cream in cake, is inadvisable and may even be dangerous. Freezing and thawing may change the composition of some foods. It usually increases the probability of prompt decay, even when it does not cause partial decomposition. Some substances, known as unorganized ferments, remain active at low temperatures at which food is kept; these may change the composition of the food undesirably.

Cold storage in market and transportation and refrigeration in the house are alike in principle, though the devices differ.