ABSTRACT
Food preservation by freezing is a process based on the effect of low temperatures in a range of –2 to –18°C for commercial purposes, although lower temperatures can be used. Food items have direct contact with the freezing medium, similar to air systems, in which the freezing process is completed very quickly, generating frozen food products of superior quality. Ultrasound is a relatively new technology, and has been applied to some foods as a pretreatment of freezing; it has proven to be very useful for controlling both the nucleation and the crystallization growth processes, by generating nucleation sites. Raw food materials change with time, the overall cost for freezing preservation being lower than that for canning and/or drying if the freezer can be kept full. Plate freezers are only suitable for regular-shaped food materials or blocks, such as fish or meat, as they favor good contact between the surfaces of the plates and the food item.
