REFRIGERATION OF FISH 515 



of water is 144 B. t. u. ; that is, 144 B. t. u. of heat must be taken out 

 of a pound of water to convert it from a liquid at 32° to a solid at 32°. 

 After it is all frozen the ice may be cooled further, but ice requires 

 only about one half B. t. u. per pound to cool it 1°. 



An example of this may help to clear the matter further. How 

 much refrigeration is required to cool 10 pounds of water from 100°, 

 freeze it, and chill the ice to 0° ? To cool the water from 100 to 

 32° would require the removal of 68 B. t. u. per pound, or 680 B. 

 t. u. To freeze the water at 32° would require the removal of 144 

 B. t. u. per pound, or 1,440 B. t. u. To reduce the ice to 0° would 

 require the removal of one-half B. t. u. per pound per degree, or 

 V 2 X 10X32=160 B. t. u. The sum of the number of B. t. u. required 

 to be removed to cool the water from 100 to 32°, to freeze it, and cool 

 the ice to 0° is thus 680+1,440+160 B. t. u., or 2,280 B. t. u. 



A ton of refrigeration is, according to accepted usage, the 

 amount of refrigeration required to freeze 2,000 pounds of water at 

 32° to ice at 32°, or 2,000X144=288,000 B. t. u. A ton of ice in melt- 

 ing absorbs 288,000 B. t. u. It will cool off 288,000 pounds of water 

 1°, or 28,800 pounds 10°, etc. 



Fish consist of 60 to 82 per cent water. Neglecting the nonwater 

 portion of, say, haddock, which contains about 80 per cent water, to 

 freeze a ton of haddock would require approximately 0.80x288,000= 

 230,400 B. t. u. of refrigeration. It is customary to consider fish as all 

 water for purposes of calculation, the difference being a safe allow- 

 ance for conservative estimates. 



WHAT HAPPENS WHEN FISH FREEZE 



What was said above about freezing substances to a solid at a 

 definite point without change of temperature until all the substance is 

 solid applies to pure simple substances like water. But a fish is not 

 all water ; it is made up of millions of microscopic cells. These cells 

 may be conveniently thought of as something like hen's eggs with 

 the limy shell removed but with the membrane lining the shell left on. 

 It would be a membranous bag inclosing a semigelatinous or al- 

 buminous substance like the white of raw egg. In fact, an egg is a 

 large cell ; reduced by millions in size and multiplied by millions in 

 number it represents fairly well what the flesh of fish is made of. 

 The gelatinous contents of these cells is about 80 per cent or more 

 water. If the fish freezes extremely rapidly, the jelly solidifies as a 

 mass of frozen jelly; but if slowly, the water has a tendency to 

 separate from the jelly as microscopic ice crystals. The water diffuses 

 out of the jelly to build these crystals larger and larger as freezing 

 proceeds, until finally a large part of the water has separated out as 

 ice. These crystals — long, sharp needles — may rupture the delicate 

 cell membranes, so that when the fish is defrosted the juice is free to 

 run out. Hence, the desirability, as will be referred to often later, of 

 the most rapid freezing. 



While pure water freezes at 32°, if anything is dissolved in the 

 water its freezing point is lowered. The water in fish contains 

 mineral and other substances in solution. The fish, therefore, does 



