352 MARINE PRODUCTS OF COMMERCE 



rotates, a pair of plates arrives at the loading slot and automatically spreads apart. 

 A tray-full of products to be frozen is placed between the plates. As the loading 

 door shuts, the drum rotates bringing another pair of the plates in the loading 

 position. When the "froster" has been completely loaded, the first plate to be 

 loaded has made a complete revolution, and during that period the product on it 

 should be frozen. The tray of frozen product is removed and a tray of unfrozen 

 product takes its place. As a rule the actual freezing operation is continuous; the 

 speed of the rotation of the drum is regulated according to the time required for 

 freezing the products. 



Freezing Fish at Sea 



As has already been indicated, fish deteriorate very rapidly after capture, even 

 if held at 32° F. If the fish are caught on vessels at a considerable distance from 

 shore and held for several days prior to landing, they will be rather stale, even 

 though kept packed in ice. The ideal way to handle fish which must be held in 

 ice for longer than a day or two is to freeze them on shipboard promptly after 

 capture. 



Prior to World War II the French (Lemon and Carlson, 1947) operated a fleet 

 of several trawlers on which fish were frozen in the North Atlantic, North Sea, 

 and Mediterranean. The Reeh system of brine freezing was used. The freezing 

 unit consisted of a cylinder, about 8 feet long and 4 feet in diameter, revolving 

 around a longitudinal axis. Each cylinder was divided by perforated partitions, 

 thus forming 8 compartments. The drum (cylinder) was filled to the axis with 

 circulating refrigerated brine. Each compartment was fitted vdth a watertight 

 door, kept closed when the drum was rotated. Each vessel had a brine tank hold- 

 ing 21 tons of saturated sodium chloride brine which was cooled to approximately 

 10° F (— 12.2° C) by evaporator coils in the tank. A centrifugal pump was used 

 to circulate the brine through the freezing drum and the brine tank. 



When caught the fish were sorted and placed in one compartment of the freez- 

 ing drum which held 550 pounds. The door was then closed and locked and the 

 drum rotated 45 degrees, thus immersing the fish to be frozen in the brine. The 

 next compartment was opened, filled, and rotated, repeating the operation until 

 the fifth compartment had reached the filling point in the cycle. The freezing 

 cylinder was so located that, when the compartments had rotated through 

 225 degrees, the opening was in the cold storage room where the frozen fish 

 were unloaded. The frozen fish were separated according to species, placed in 

 net bags containing about 50 pounds, and stored in the refrigerated hold. From 

 1 to 2 hours were required to freeze the fish. The total freezing capacity of this 

 trawler was 20 tons per day. 



A number of the tuna-fishing vessels of Southern California immediately freeze 

 each catch by placing the fish in tanks or "wells" through which chilled sea 

 water 28° F (— 2.2° C) is rapidly circulated. When the compartment has been 

 filled with fish, the chilled sea water is pumped overboard and freezing is 

 effected by circulating concentrated sodium chloride brine at about 4° F 

 (— 15.6°C). The fish are brought down to a temperature of about 0° F 

 (— 17.8° C), then the cold brine is returned to a storage well and the fish held 

 dry at approximately that temperature. 



Tuna frozen in this way is used almost exclusively for canning. Some salt 



