The frozen-food chain typically consists of the following links: freezing, storage in refrigerated warehouses, display in a refrigerated case at food markets, and finally storage in the home freezer or frozen-food compartment of a domestic refrigerator. Freezing Early attempts to freeze food resulted in a product laced with ice crystals until it was discovered that the temperature must be plunged rapidly through the freezing zone. Approaches to freezing food include air-blast freezing, where air at approximately -30°C is blown with high velocity over packages of food stacked on fork-lift pallets; contact freezing, where the food is placed between metal plates and surfaces; immersion freezing, where the food is placed in a low-temperature brine; fluidized-bed freezing, where the individual particles are carried along a conveyor belt and kept in suspension by an upward-directed stream of cold air; and freezing with a cryogenic substance such as nitrogen or carbon dioxide.

Storage Fruits and vegetables should be frozen quickly after harvesting and meats frozen quickly after slaughter to maintain high quality. Truckload and railcar-load lots are then moved to refrigerated warehouses, where they are stored at -20 to -23°C, perhaps for many months. To maintain a high quality in fish, the storage temperature is even lower.

Distribution Food moves from the refrigerated warehouses to food markets as needed to replenish the stock there. In the market the food is kept refrigerated in display cases held at 3 to 5°C for dairy products and unfrozen fruits and vegetables at approximately -20°C for frozen foods and ice cream. In the United States about 100,000 refrigerated display cases are sold each year.

The consumer finally stores the food in a domestic refrigerator or freezer until used. Five million domestic refrigerators are sold each year in the United States, and for several decades styling and first cost were paramount considerations in the design and manufacture of domestic refrigerators. The need for energy conservation,11 however, has brought back the engineering challenge in designing these appliances.