REFRIGERATION OF FISH 617 



fish lost 16 per cent in weight, and on being taken from the box and 

 unwrapped they lost 7.8 per cent, or 23.8 per cent loss between the 

 frozen boxed fillets and the defrosted and unwrapped condition. If 

 fish like halibut are steaked before defrosting, the loss will be greater 

 than in fish not cut, because the skin of the latter helps to hold the 

 juice until it can be reabsorbed. 



If drying has been allowed to occur in storage, the fish will have 

 lost some weight. Some of this lost weight can be restored to the 

 fish as it defrosts, either by condensation of atmospheric moisture on 

 the cold fish, by embedding the fish in ice, or by immersion in water. 



METHODS OF DEFROSTING 



These are (1) allowing the fish to remain in warm air, (2) 

 putting it in cool air in a refrigerator, (3) embedding in cracked ice. 

 and (1) immersing in water. 



1. When fish are left in the air of a room at ordinary temperature 

 a considerable amount of water will condense on the surface, and 

 some of it will be absorbed by the fish, especially if the fish has dried 

 in storage. This gain may be from 1 to 3 per cent. Air defrosting, 

 like air freezing, is slow, and for the same reasons, but it allows time 

 for the reabsorption of the separated juice. There may be some dry- 

 ing of the surface if the thawing time is prolonged, with consequent 

 impairment of appearance. To prevent this, the fish may be covered 

 with a damp cloth. 



2. Defrosting in a refrigerator or cold chamber is similar to de- 

 frosting in a warm room, but is slower. It offers a slight advantage, 

 perhaps, in protecting the fish from bacterial infection and from 

 surface drying, to both of which it is exposed in a warm room. 

 Otherwise there seems to be no particular advantage in this method. 



3. The freezing point of fresh- water fish is about 31° and of salt- 

 water fish about 30° F. Fish will therefore defrost slowly when 

 embedded in cracked ice that has a temperature of 32°. This 

 method is still slower than defrosting in a refrigerator. It exposes 

 the fish to water from melting ice. Some of this water is taken 

 up by the fish, with a consequent gain in weight, to a greater extent 

 than when the defrosting is done in air. Also some of the soluble 

 substance is dissolved from the superficial parts of the fish. Cut sur- 

 faces are blanched and their appearance is not improved. Still, the 

 slowness of the method allows time for the reabsorption of the 

 juices. 



4. Immersion in cold water is the quickest method and perhaps 

 the one in most common use. The fish absorb water up to as much 

 as 10 per cent of the original weight, restoring loss if any occurred 

 in storage. If the fish dried very much in storage, the loss may not 

 be completely made good. In this method also some soluble sub- 

 stances are removed from the fish. This effect may be diminished 

 by adding a small amount of common salt to the water. The amount 

 of salt required would be about 0.7 pound to 100 pounds of water 

 for fresh- water fish, or about 1.3 pounds of salt to 100 pounds of 

 water for sea fish. 



The reader who is interested in the theoretical principles involved 

 in thawing is referred to Stiles 83 and to Plank, Ehrenbaum, and 



' See footnote 47, p. 583. 



