FREEZING AND COLD STORAGE 301 



the cooling solution. Immersion freezers are ideally suited for use in freez- 

 ing unpackaged fish on the vessel, where compactness of equipment, fast 

 rate of freezing, and high efficiency of operation are of prime importance. 



The cooling solution is the heart of the immersion-freezing system. To 

 be acceptable, the solution directly contacting the food must meet Food 

 and Drug requirements and be easy to renew, relatively inexpensive, and 

 of low temperature and viscosity. These demanding requirements are not 

 easy to fulfill, and sodium chloride brine is still the solution used primarily 

 in the immersion freezing of fish. More recently, solutions consisting of 

 20 per cent glucose and 20 per cent salt in water have been used success- 

 fully in the freezing of shrimp on the vessel. Glycol and glycerine solutions 

 are being used in freezing packaged poultry; however, they are not being 

 used for seafood. 



Tuna are frozen on the vessel in brine wells lined with galvanized pipe 

 coils on the inside. Direct expansion of ammonia into these coils cools the 

 brine, which is circulated by a pump over the coils and the fish. In some 

 cases a heat exchanger or brine cooler is used to obtain more rapid cooling 

 of the brine and, consequently, the fish. In commercial operation the fish 

 are placed in sodium chloride brine in the wells. Then, after freezing, the 

 brine is pumped overboard and the pipe coils used to keep the well re- 

 frigerated to 10 or 15°F. Prior to unloading, the wells are filled with brine 

 to thaw the fish for processing at the cannery. 



Commercial equipment is available for the freezing of shrimp aboard 

 the vesseP^. One system in general use consists of a stainless steel tank 

 containing a pipe-coil evaporator. A glucose-salt brine circulates within 

 the tank over the evaporator coils, which are cooled by Refrigerant 12 or 

 22, and over shrimp contained in wire baskets of 50- or 25-pound capacity. 

 About 15 minutes is required to freeze the product satisfactorily. 



A brine immersion-freezing system for freezing groundfish at sea has 

 been developed by the U.S. Bureau of Commercial Fisheries and put into 

 experimental use on the MV Delaware. Researchers at the Bureau's 

 Gloucester Technological Laboratory found that groundfish such as cod 

 and haddock could be put whole into cylindrical baskets in the freezing 

 tank, the baskets moved through the cold brine, and the fish frozen very 

 rapidly. After freezing, the fish could be stored, until processed, at 0°F in 

 the vessel's hold and in a frozen storage plant ashore. The frozen fish can 

 be water-thawed, filleted, and the fillets refrozen and marketed through 

 regular distribution channels. 



Cold-storage Design and Equipment 



A cold-storage plant, or refrigerated warehouse, consists essentially of 

 an envelope of insulation enclosing partitioned rooms that are cooled with 



