REFRIGERATION OF FISH 549 



glaze. This calculation is only illustrative, however, and does not 

 necessarily represent what actually happens within the fish. It is 

 more probable that at the beginning not all the water in the fish is 

 frozen ; the ice present is in equilibrium with concentrated fish juice. 

 As the fish absorbs heat from the freezing glaze, some of the internal 

 ice thaws, absorbing latent heat, with a corresponding dilution of the 

 juice and rise in temperature. 



At any rate, it is much better to derive part of the refrigeration 

 from the surrounding air for freezing the glaze. While glaze will 

 form on the thicker parts of the fish in. comparatively warm air by 

 warming the fish, the thin parts — fins, tail, and snout — -will not glaze 

 at all, because these parts do not contain sufficient refrigeration. 

 They can be covered with glaze only in air cold enough to freeze the 

 water. The freezing point of water being 32°, it might seem that 

 air slightly below this temperature would be sufficient; but water 

 drains off rapidly when fish are withdrawn from the water, and at 

 too high a temperature too much of the water runs off before it has 

 frozen, consequently the glaze is thin. Several quick dips with short 

 intervals between in the cold-room air are better than one long dip 

 in the trough. These several dips allow freezing of the glaze partly 

 by the cold air rather than entirely by the fish. 



The temperature in the glazing room should be low, therefore, 

 and might be very low as far as the glazing itself is concerned; but 

 workers object to remaining for long periods in very cold rooms. A 

 temperature of from 12 to 15° has been found to be satisfactory, 

 producing a good glaze and being not too cold for the workers if 

 they remain vigorously active. 



It is contended by some that because when fish come from the 

 freezer they are not of uniform temperature throughout, further 

 freezing of the inner portions occurs after they are placed in the 

 cold-storage room, which causes further expansion that cracks the 

 glaze. They should not be glazed at once but allowed to come to a 

 uniform temperature in the storage-room air before the glaze is 

 applied. There may be something in this objection to the practice 

 now followed, but it is academic, for it would be commercially 

 expensive to store loose or boxed fish and then handle them all over 

 again for glazing. 



TEMPERATURE OF GLAZING WATER 



The glazing water should be clean, wholesome water of 35 to 40° 

 temperature. In some plants warmer water is used. If operations 

 are begun with warm water, ice is added to cool it; in this case snow 

 from pipe coils should not be used, as it forms a mush that sticks to 

 the fish, making a rough surface. However, as glazing proceeds, the 

 water is chilled rapidly by the cold cakes of fish passing through it. 

 When the water approaches the freezing point, a pebbly glaze is 

 produced. The water must therefore be kept slightly warmer, pref- 

 erably at about 35° F., by the continuous flow of a small amount of 

 warmer water into the glazing tank. 



THICKNESS AND AMOUNT OF GLAZE APPLIED 



The cakes of fish are left in the water for from a few seconds to a 

 minute at a time. It is inadvisable to leave them in longer. The con- 



