544 U. S. BUREAU OF FISHERIES 



tion, etc. It is highly desirable to maintain a maximum temperature 

 not above 0° F. during the freezing process. 



There are also few data on the amount of time required to freeze 

 fish in air. Pans of fish usually are allowed to remain on the sharp 

 freezer for 24 to 36 or even 48 hours when the temperature is not 

 low. Panned fish, small, and large fish freeze in about the same 

 length of time, but if frozen separately small fish freeze much more 

 rapidly than large ones. 



In rooms refrigerated by direct expansion it is a common practice 

 to stop flow of the ammonia while the rooms are being loaded. After 

 the fish are on the shelves the doors are closed and the expansion 

 valves opened. The room begins to cool and reaches a fairly constant 

 temperature at several degrees above zero, where it remains for several 

 hours, until the fish are nearly frozen. The temperature then drops 

 gradually until it reaches, say, 10° below zero, when the fish are 

 considered to be frozen. The ammonia is again turned oif and the 

 fish taken out. If the doors are left open, the snow on the coils 

 thaws and there is much drip. The coils, being clean, absorb heat 

 faster but also appear to take up moisture faster. 



In rooms refrigerated by brine the brine is allowed to run con- 

 tinuously and the rooms are always cold. In such a case freezing 

 begins at a lower air temperature and probably progresses more 

 rapidly. As the snow on the pipes rarely thaws, it becomes very 

 dirty from drip from the pans. It should be removed occasionally 

 by shutting off the brine and warming up the room, or by an ac- 

 cessory circulation of warm brine through the pipes. 



PLACING THE FISH IN THE SHARP FREEZER 



In most cases the fish are trucked into the freezers, where the pans 

 of fish are transferred from truck to coils. Sometimes a small door 

 is let into the large freezer door, through which the fish may be 

 passed without entailing a great loss of cold air. A few freezers 

 have a roller conveyer leading from this small door along the corridor 

 of the freezer. Operators receive the pans from the roller conveyer 

 and place them on the shelves. (See fig. 7, p. 531.) The pans should 

 rest directly on the coils. Sometimes, when freezer space is limited 

 the pans are placed one on another; but this practice is obviously 

 bad because, it will be remembered, the heat must pass out through 

 the surface of the fish. Stacking pans two deep eliminates the bottom 

 of one and the top of the other as available surfaces — nearly half the 

 total surface — and retards freezing in the same proportion. 



For large fish, where pans are not used, there are provided gal- 

 vanized-iron sheets that are laid on the coils. (Fig. 14.) The fish 

 are laid on these metal sheets in such a way that they do not freeze 

 together. Still larger fish, such as whale halibut, swordfish, and 

 sturgeon, are laid on the floor or on boxes or battens to freeze or else 

 they are suspended. Large fish like these freeze in 2 to 4 days at a 

 sufficiently low temperature. 



Herring for bait are not panned but are dumped en masse on 

 wooden flakes. If on iron sheets they stick and are difficult to remove. 



Shucked oysters in 1-gallon tin cans are simply placed in the sharp 

 freezers on the shelves or floor and allowed to freeze. Clams and 

 scallops are treated in the same manner, the latter sometimes being 

 frozen in muslin bags. 



