REFRIGERATION AND FREEZING OF FISH 349 



temperature of the brine is usually maintained considerably below 0° F 

 (— 17.8° C); the lower the brine temperature, the greater the capacity of the 

 apparatus. Kolbe's system is a relatively simple way of freezing fillets, steaks, 

 and individual fish. 



Freezing Packaged Fish 



Cold Plate Freezing. Refrigerated, thin, corrosion-resistant metal plates are often 

 used for freezing foods in locker plants and small cold storages. Two common 

 makes of these plates are the "Kold-Hold Serpentine Plates" and the "Dole 

 Vacuum Cold Plates." "Freon-12," or some other primary refrigerant, is circulated 

 through a series of plates. Because of the rapid conduction of heat from the food 

 being frozen by the thin metal plate, rapid freezing is obtained. In some installa- 

 tions the rate of freezing is hastened still further by an air blast from a fan or 

 blower. These plates may be used to freeze fish or fishery products either before 

 or after packaging. 



The Murphy Freezer. In 1933 Murphy designed a freezer in which the product 

 is frozen on coils of refrigerated pipes of rectangular cross-section. These are 

 arranged in shelves staggered one over the other to provide a sinuous passage for 

 a cold air blast. Blower fans are placed at the ends of the chamber to force cold 

 air over the product. Thus the products are frozen by conduction of the heat from 

 the under side and by convection from the upper side. The cold air is circulated 

 first over the bottom coil and then over the next one above and so on until it 

 reaches the top cooling coils where it is refrigerated and returned thiough the 

 system. The product to be frozen, either packaged or loose, is placed on trays 

 which are then put on the pipe shelves. 



"Birdseye" Systems. Clarence Birdseye developed 2 diflFerent types of freezing 

 machines for freezing both fish and other products. The first is known as the 

 double-belt freezer and the second the multiplate freezer. Although these ma- 

 chines are of entirely different design, the freezing is accomplished by the same 

 principle— that of extracting heat by conduction through movable metal plates 

 which exert pressure on the product being frozen. 



The "Birdseye" double-belt freezer is used to freeze both round and packaged 

 fish and fishery products. This freezer consists of endless corrosion -resistant metal 

 belts running at the same speed and in the same direction through an insulated 

 freezing tunnel. The usual length of the freezing area is 50 feet. The lower belt 

 is usually 36 inches wide and the upper one 44 inches wide. The food to be 

 frozen is placed on the upper side of the lower belt (which extends out beyond 

 the upper belt) and is automatically engaged with the desired pressure by the 

 upper belt and carried into the freezing zone. Calcium chloride brine, refrigerated 

 to about — 50° F (— 45.6° C), is sprayed on the under surface of the lower belt 

 and on the upper surface of the upper belt. The upper belt is wider than the 

 lower belt so that the brine falls directly from its turned-down edges into a 

 shallow tank under the lower belt. The double-belt freezer will take products of 

 any thickness. As a rule the belts are not moved continuously; the freezer is filled 

 with products to be frozen, then the belt is allowed to remain stationary until 

 the charge is frozen. The belts are then operated until the frozen products have 

 been moved out and a new charge put in. The double-belt freezers have been 

 largely replaced by the more compact multiplate machines. 



