346 MARINE PRODUCTS OF COMMERCE 



slower the freezing, the larger the crystals. When the fish are defrosted, not only 

 is the juice, containing flavoring matter, lost, but the fish spoil much more rapidly 

 in consequence of the damage done to the cellular structures by the ice crystals. 

 These changes seriously limit the frozen fish business. Therefore, the principal 

 steps taken to improve freezing methods aim at securing more rapid freezing. 



Brine is a much better conductor of heat than air, and has a much greater 

 specific heat. Therefore, fish immersed in brine of about 0° F (— 17.8° C) will 

 freeze very much faster than in air at the same temperature. Although substances 

 other than salt have been proposed (e.g., glycerin, alcohol, magnesium chloride, 

 etc. ) , salt is the only substance used so far which answers all the requirements of 

 freezing point, low price, and palatability. 



In Norway some fish are frozen in brine, made by mixing salt and crushed ice 

 according to a method invented by Nekolai Dahl. This procedure simply involves 

 the pumping of brine around thfe fish packed in shipping boxes. 



Brine freezing of fish was introduced into the United States in 1918, but has 

 never attained general usage. From the standpoint of flavor the quality of brine- 

 frozen fish is high, although their exterior, which is in contact with the brine, 

 may be a little salty. One reason why brine freezing has not been generally used 

 in this country is that the method is not adaptable to the freezing of fillets and 

 steaks. 



The introduction of brine freezing and the somewhat later introduction of fillet- 

 ing (about 1925) into the United States acted as a spur to research on other rapid 

 methods of freezing which quickly remove heat without direct contact of the 

 fish with the brine. These methods of quick freezing will be considered in detail 

 later in this chapter. 



The "Z" Method. M. T. Zarotschenzeff developed a brine-freezing process in 

 which the fish or other foods are frozen in a spray or "fog" of sodium chloride 

 brine. Three diff^erent types of apparatus have been devised by Zarotschenzeff. 

 One consists of a cabinet with a number of separate compartments in which are 

 placed wire mesh trays filled with the product to be frozen by the spray of re- 

 frigerated brine atomized from properly located nozzles. The second type of "Z" 

 freezer is a large chamber or tunnel into which are pushed trucks loaded with 

 trays of the product and sprayed with the refrigerated brine. The third type of 

 apparatus consists of a wire mesh belt conveyor which transports the product 

 through a tunnel in which the refrigerated brine is atomized. The brine which 

 collects on the bottom is refrigerated, recirculated, and atomized. The usual tem- 

 perature of the spray is to - 3° F (-17.8 to - 19.4° C). 



The University of Texas Polyphase Quick Freezing System, also known as the 

 "Bartlett Freezer," has been devised for the rapid freezing of shrimp, although it 

 is also used to a limited extent for freezing other foods. Bartlett and Woolrich 

 (1942) describe this freezer as follows: It consists of a refrigerant-jacketed hori- 

 zontal tube, partly filled with the polyphase medium, inside which a closely fitting 

 helicoid conveyor operates. This tube terminates in feed and discharge compart- 

 ments which are connected by a return conduit. The discharge compartment is 

 equipped with a suitable grid which is periodically traversed by a raking device. A 

 circular oscillation is superimposed upon the normal rotation of the conveyor 

 screw to provide the necessary agitation. This motion removes the fluid film and 



