Freezing is a unit operation where the temperature of the food is decreased below its freezing point and during which part of the water content changes state, forming ice crystals. The immobilization of water in ice and the consequent concentration of the solutes dissolved in non-frozen water, lower the food aw, inhibiting the growth of microorganisms and enzyme activity. The preservation is therefore reached by the combination of temperature, reduction of aw and in some foods the applied pre-treatment (blanching).
This type of freezers, utilize cold air at high speeds and may be designed in various configurations. They are used to freeze very dense products or products packed in big packages which can be placed on conveyor belts and exposed to the high speed flowing air.
Tunnel and spiral type are the representative air blast freezers, separately, depending on the freezing scale and space limited.
The fluidized bed freezer is only a modified version of an air blast freezer in which the products are frozen by fluidization in air at very low temperature. The size (density) of the product to be frozen is limited by the energy needed to produce the required air velocity for fluidization. The frozen product is commercially designated by instant-quick-frozen (IQF) (Heldman and Singh, 1982).
