What are the different freezing methods?

Following are two methods mainly used for food freezing –

• Slow or sharp freezing – in the slow freezing, the food products are placed in a low temperature room and allowed to freeze slowly in still air by natural convection. The temperature maintained in sharp freezers range from (-) 170C to (-) 400C. Since te circulation of air in the stored room is by natural convection, therefore the time required for freezing the food is considerable large. This methods is commonly used for beef and pork, boxed poultry, fish, fruit in barrels and other large containers and eggs in cans.
• Quick Freezing – In the quick freezing method for freezing the food products in storage the forced circulation of cold air is necessary.
• Immersion Freezing (Cryogenic freezing) – In this method of quick freezing, the food product are immersed into a low temperature liquid. The liquid are good conductor of heat and is in good thermal contact with all the product. Therefore the heat transfer is rapid and the product is completely frozen in a very short time. He fish and shrimp are the two animal product which are frequently frozen by immersion.
• Indirect contact freezing - In this method of quick freezing, the food product is freezed by the direct contact with the metal surface cooled by any of the refrigerant such as ammonia , R22. Brine. i.e. Plate freezer
• Air blast freezing – in this method of quick freezing, the food products are freezed by the contact with the cold air. The air blast freezing is widely used because it provides excellent quality of the food among all other types. In this method very low temperature air circulated with high velocity. The air blast freezing is mainly used for freezing fishery products like shrimp, fish, fillets, steaks, scallps etc.

Note: - The difference between quick and slow freezing is only in size of ice crystal formed within the food during freezing.

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