FOOD FREEZING

Food products should be stored at approx -15 Deg or below in order to preserve them in their original fresh state for longer periods.Such storages are known as frozen storages. Products which are commonly preserved in frozen storage includes fruits,vegetables,fruit juices,meat,poultry,bread,pastries,and wide variety of pre-cooked foods.
Vegetables and fruits to be frozen should be harvested at the peak of maturity and frozen as quickly as possible after considerable processing(cleaning,washing,blanching in hot water etc )

Methods Of Food Freezing

1. slow/sharp freezing : Food products are placed in low temperature rooms and allowed to freeze by the aid of natural convection. Temperature at a range of -17 deg to -40 deg is maintained.Time required for this type of freezing is considerably large.It may be from three hours to three days depending up on the bulk of products & conditions in the freezer.

2. Quick Freezing : In this method forced circulation of cold air is necessary.Quick freezing is generally done in

(a) Immersion Freezing : Food products are immersed into low temperature liquids,liquid medium used should be non-toxic and not produce any bad effect on the immersed foods.Liquids used for this purpose are sodium chloride,brine,propylene glycol etc.This freezing method produces a thin coating of ice on surface of product resulting in prevention of dehydration.

(b) Indirect Contact Freezing : Food product is freezed by the direct contact with metal surface cooled by any of refrigerants such as ammonia ,R-12, R-22 etc. For this purpose various types of plate freezers consisting of metal plates with storage space and refrigerant circulating through them are used.

(C) Air Blast Freezing : Food products are freezed by contact with cold air.Air blast freezing is widely used because it provides excellent quality of good among all other types.In this method,a very low temperature air is circulated with a very high velocity,around all parts of product kept in insulated storages.Velocity of air varies from 30m/min to 120m/min according to the type of food to be freezed.Air blast freezing is used for freezing fishery products like shrimp,fish fillets,streaks,scallops or pre-cooled products .