Cryogenic Freezing, as you would realize, is one of the fast, flexible and cheap method of freezing. In this, the liquefied gases are placed in direct contact with the foods. Food is exposed to an atmosphere below - 60°C through direct contact with liquid nitrogen or liquid carbon dioxide or their vapor. This is a very fast method of freezing, thus adequate control is necessary for achieving quality products. It also provides flexibility by being compatible with various types of food products and having a low capital cost. The rapid formation of small ice crystals greatly reduces the damage caused by cell rupture, preserving color, texture, flavor and
nutritional value. The rapid freezing also reduces the evaporative weight loss from the products, provides high product throughput and has low floor space requirements.
The cryo-mechanical technique utilizes a cryogenic gas to create a frozen crust on a fluid product, after which the product may be conveyed to a conventional mechanical freezer. The advantages of liquid nitrogen are that it is colorless, odorless and is chemically inert and boils at 195.8°C. It is usually used for high-value products due to the high capital cost for gas compression. The product can be exposed to a cryogenic medium in three was:
(a) The cryogenic liquid is directly sprayed on the product in a tunnel freezer.
(b) The cryogenic liquid is vaporized and blown over the food in a spiral freezer or batch freezer.
(c) The product is immersed in the cryogenic liquid in an immersion freezer.