280 PRESERVATION METHODS 



Refrigerated Sea Water (RSW): The cooling of fish in chilled, circu- 

 lating sea water at 32°F is more efficient than is cooling in crushed ice 

 under usual commercial conditions. In icing fish aboard the vessel, the 

 best results are attained if ice completely surrounds each fish. In practice, 

 this ideal icing is difficult to attain, and a layer of fish tends to build up 

 through which the melt water from the ice percolates. The cooling medium 

 in the case of circulating refrigerated sea water surrounds the fish entirely, 

 and thus the transfer of heat from the fish is more rapid in the chilled sea 

 water. Moderate circulation of chilled sea water through the mass of fish 

 and past the cooling coils is essential to achieve a uniform temperature of 

 29 to 30°F at all times. 



The problems of refrigerating a hold for sea-water storage are somewhat 

 greater than are those of ice storage, as the hold must not only be con- 

 structed water-tight but must be subdivided into sections or tanks with 

 suitable baffles. Large centrifugal-type pumps are needed for pumping 

 water in or out of the separate tanks and to and from the brine chiller 

 or heat exchanger. Special equipment must be designed for discharging 

 and unloading the fish. The water in the tanks is precooled to about 29°F 

 prior to being loaded with fish. Ice may be carried to supply additional 

 refrigeration if large volumes of fish must be handled in a short time. If 

 preferred, three per cent of salt (0.25 pounds of sodium chloride per gallon 

 of water) may be used instead of sea water. 



Comparison of keeping qualities of fish in refrigerated sea water (or 

 three per cent brine) and ice^ indicate that sea water has no special prop- 

 erties for extending the storage life if fish is of the same temperature in 

 each case. From the viewpoint of keeping quality, the real advantage of 

 refrigerated brine appears to be that the brine temperature can be lowered 

 to 29 to 30°F, or just above the point at which the fish begin to freeze. 

 The importance of this characteristic is related to the fact that bacterial 

 and enzymatic activity are greatly depressed at temperatures slightly 

 below 32°F and greatly increased at temperatures slightly above 32°F. 

 For example, Canadian workers found that cod and haddock fillets kept 

 eleven to twelve days at 31.5°F but only five to six days at 37°F. At 45°F 

 the keeping time was only two to three days^. 



The use of the RSW system is advantageous commercially in that the 

 fish may be transferred to tanks with far less labor than icing re(iuires. 

 The brine supports the fish and minimizes physical damage and pressure 

 effects that may occur in the deep layers of iced fish; however, the effect 

 of brine on flesh composition should be considered. The influence of salt 

 in the brine during RSW storage of pink salmon increased the ash and 

 sodium content greatly, whereas salmon in ice showed extensive leaching 

 of the ash, sodium, and potassium contents ^^ The technological aspects 



