REFRIGERATION OF FISH 535 



lated, all the pipes are filled with the refrigerating medium and are 

 therefore effective. In direct expansion systems a deficient charge 

 of ammonia or improper regulation of the expansion valves may 

 give rise to a condition wherein only a part of the piping is actually 

 effective. For example, the writer has seen a sharp freezer heavily 

 piped but with a temperature far too high. Examination revealed 

 that all the ammonia admitted to the coils evaporated in three turns 

 of pipe, and only these three were frosted. Further, really efficient 

 operation of an ammonia machine requires skill, understanding, and 

 watchfulness on the part of the operator. These qualities are more 

 likely to be manifest if there is one expansion valve under his imme- 

 diate care in the engine room than if several are located in various 

 parts of the building. Another reason for preferring brine, es- 

 pecially in sharp freezers, is that the large volume of cold brine in 

 the pipes prevents an excessive rise of temperature when the rooms 

 are first loaded. The higher first cost of apparatus for brine circu- 

 lation is justified in most cases by the more satisfactory operation. 



Air washers, deodorizers, and dehumidifiers are not used and 

 appear to be unnecessary in fish-freezing plants. Deficient rather 

 than excessive humidity occurs in the rooms, but no satisfactory 

 mechanical means has been devised for correcting this trouble. 

 Drip pans sometimes are placed under the pipes but appear to be 

 unnecessary, except in cool rooms kept above the freezing point of 

 water; and even then, if the pipes remain frosted, they are not 

 needed. 



PRACTICAL FREEZING METHODS 



FREEZING IN COLD ROOMS 



As freezing in cold rooms is in almost universal use in the United 

 States, the method will be described in detail, together with all 

 necessary operations, some of which apply also to other methods 

 that will be treated later. 



RECEIVING AND INSPECTION 



If the fish are received from the hold of a boat, usually they are 

 hoisted mechanically to the platform. For salmon a satisfactory 

 hoisting vessel is a wooden box lined with galvanized sheet iron. 

 The ends of the box slopes outward and a rope is fastened by a 

 hook in a ring at each end. When one end of the box is released 

 on the platform and the other lifted, the salmon slide out easily 

 and without impact. Halibut are hoisted by a 6-inch mesh cargo 

 net woven of ^-inch manila rope, which, when caught by hooks at 

 the corners, makes a large bag. This serves to hoist large quantities 

 of halibut but seems to squeeze the fish against the ropes excessively. 

 In most commercial freezers the fish arrive in boxes or barrels, iced. 

 Immediately upon being landed western halibut are beheaded, the 

 head portion is lifted with a meat hook, and the head is cut off with 

 a butcher knife. 



Before the fish are accepted they are, or should be, inspected for 

 quality. It can not be repeated too often or too emphatically that 

 this inspection should be severe. The temptation to save their fish 



