REFRIGERATION AND FREEZING OF FISH 



347 



the freshly formed ice crystals from the refrigerated surfaces, thus materially in- 

 creasing heat transfer. A suitable mechanism regulates the rate of travel through 

 the tube to allow complete freezing of the various sized particles. After the 

 desired chilling has been accomplished, the food is removed from the body of 

 the medium and allowed to drain in a refrigerated compartment. A very slow 

 agitation during this step of the process facilitates the removal of the adhering 

 fluid. If desired, a more vigorous means, such as an air blast, may assist the 

 gravity draining (Bartlett and Woolrich, 1941). 



For a detailed account of the various other brine-freezing processes, the reader 

 is referred to the first edition (1923) of "Marine Products of Commerce." 



The Petersen Freezer. According to the Petersen method, which is used in freez- 

 ing some fish in the Great Lakes Region, the fish are frozen singly or in blocks in 

 deep, elongated, narrow metal cans placed in tanks of calcium chloride brine at 

 — 20 to — 30° F (— 28.9 to — 34.4° C) in a manner similar to that employed in 

 making ice. In order to handle fish of varying sizes several sets of different sized 

 cans are employed. One common size produces cakes 2 inches thick, 28 inches 

 long, and 18 inches wide. The frozen blocks of fish are removed by slightly warm- 

 ing the cans in water or brine above 32° F (0° C), after which the cans are in- 

 verted, permitting the block of fish to slip into the glazing tank. 



40 



30 



I 



-I 



5 

 Hours 



{Courtesy Detvcy and Almy Co.) 



Fig. 16-7. Curves showing rate of freezing of fillets in air blasts of 

 different velocities. The fillets were frozen in stainless steel trays, 2/2" deep, 

 in air at -18° F (-27.8° C). 



Air-Blast Freezing. Freezing may be greatly hastened by the use of rapidly 

 moving, intensely cold air. A cold air blast is usually obtained by directing air 

 from a blower through coils refrigerated by ammonia, "Freon," or some other 

 refrigerant. In the Pacific Northwest some panned fish and panned fillets are 

 frozen in covered aluminum pans placed on movable racks or buggies in Frick 



