REFRIGERATION OF FISH 



573 



as the square of the diameter. Thus, a ball 4 inches in diameter has 

 four times the surface and eight times the volume of a 2-inch ball; 

 or. that is, the 2-inch ball has twice as much surface in proportion to 

 its volume as the 4-inch ball has. Likewise, a fish 1 foot long has 

 twice as much surface in proportion to volume as a 2-foot fish of the 

 same kind. 



The amount of heat in a fish is proportional to its volume; but 

 as the fish freezes the heat must pass through the surface, and this 

 surface is proportionately smaller the larger the fish. In the table 

 it is apparent that a fish twice as thick as another freezes only about 

 half as fast in air; but the same ratio is not apparent when the 

 freezing is done in brine, where doubling the thickness approxi- 

 mately triples the time required to freeze. The reason for this is 

 that in air freezing, which is very slow, the heat has time to be 

 conducted from the inner parts of the fish to the surface, and the 

 amount of surface exposed will determine how long it takes the fish 

 to freeze. But in brine the surface very quickly reaches the tempera- 

 ture of the brine, and the heat must then be conducted from some 

 distance through a shell of frozen tissues; the area of surface thus 

 has relatively less to do with the rate of freezing in brine, and the 

 heat conductivity relatively more, than in air. Thus, a fish 2 inches 

 thick will freeze in brine about 13 times as fast as it will in air, 

 while a 4-inch fish will freeze only about 8.8 times as fast. A fish 

 10 inches thick would freeze only about 4.5 times faster in brine 

 than it would in air, the air and brine being, of course, at the same 

 temperature. These same remarks apply to the packing of small 

 fish in pans or molds. This practice has the effect of making a 

 larger fish of several small ones, reducing the surface exposed and 

 lowering the rate of freezing. 



The rate of movement of the brine, is also highly important in 

 determining the rate of freezing in brine, as illustrated in Table 19, 

 taken from the work of Dunkerley. 3 - 1 As will be seen later, this 

 fact is of the greatest importance in the design and operation of brine 

 freezers. 



Table 19.— Time required to freeze fish in brine. (From Dunkerley.) 



Thickness of 

 fish in inches 



1... 



v/ 2 . 



2 



VA- 



3... 



V4- 



Still brine at 

 10° F. 



Hours 

 

 

 1 

 1 

 2 

 3 



Minutes 

 25 

 45 

 20 

 50 

 35 

 15 



Brine at 10° F. 



moving 3 feet 



per second 



Hours 

 

 

 

 1 

 1 



Minutes 

 14 

 26 

 50 

 15 

 45 

 18 



Thickness of 

 fish in inches 



4H 

 5.. 



6.. 



Still brine at 

 10° F. 



Hours 

 4 

 5 



Minutes 

 10 

 

 

 

 15 



Brine at 10° F. 



moving 3 feet 



per second 



Hours 

 3 

 3 

 4 



Minutes 

 

 45 

 37 

 30 

 30 



Dunkerley also gives the following formula for calculating the 

 time required to freeze fish at any temperature if the time required 

 to freeze in brine at 10° F. is known. His formula is : 



Time= 



(Time at 10° F.)X20 



30 — (Brine at desired temperature) 



■■» " Fish freezing in brine," by H. M. Dunkerley. Fish Trades Gazette and Poultry, 

 Game, and Rabbit Trades Chronicle, Mar. 30, 1918, p. 19. London. 



