294 PRESERVATION METHODS 



The use of hermetically sealed tin containers will significantly increase 

 the frozen storage life of fatty fish or other fish and shellfish not readily 

 amenable to freezing. However, despite these advantages, these containers 

 are seldom used for frozen seafoods, probably because of their high cost 

 and association with heat-processed foods. Fatty fish can also be well pro- 

 tected by using vacuum-pack or heat-shrinkable bags, where the air is 

 removed from the package and the film shrunk tightly around it by im- 

 mersion in hot water or passage through a steam chamber. Also, instead 

 of vacuum packaging, the package can be purged with nitrogen gas to 

 remove the oxygen. Pouches and bags made of polyester films coated with 

 or laminated to polyethylene, cellophane, polyvinylidene chloride, alumi- 

 num foil, or certain combinations of these materials are quite satisfactory. 



Another method of packaging fatty fish is to dip the product into a 

 protective alginate or other solution, package it, fill all voids with the 

 dipping solution, overwrap the carton, and freeze the product. An alter- 

 nate method consists of individually freezing the product, packaging it, 

 flooding the cartons with a glazing solution, overwrapping the cartons, 

 and refreezing the product or putting it into low-temperature frozen stor- 

 age. The above methods have been used quite successfully for packaging 

 frozen shrimp, salmon, mackerel, smelt, and herring. 



The so-called nonfatty products such as haddock, cod, certain shellfish, 

 and precooked fish must be protected principally against loss of moisture; 

 in some cases, however, oxidation can also be a serious problem. The 

 packaging requirements for these fish and shellfish are less demanding 

 than those for fatty fish; therefore, conventional cartons and overwrap- 

 ping films can be used satisfactorily. Fish fillets, breaded convenience 

 items, or steaks can be adequately protected by packaging in tightly fitted 

 waxed cartons overwrapped with waxed bleached sulfite paper, combina- 

 tions of waxed paper, polyethylene, aluminum foil, or cellophane. The 

 new cook-in-the-bag package being used for shrimp, fillets, and other 

 heat-and-serve seafoods offers considerable promise. Materials such as 

 polyethylene and combinations of foil, polyethylene, and paper are being 

 used quite satisfactorily for this purpose. 



Glazing. The function of a glaze is to provide a continuous film or 

 coating that will adhere to the product and retard loss of moisture or 

 oxidation. Glazes are, in the main, applied to whole or eviscerated fish, 

 although in some instances they are used for packaged fish. Application 

 is by dipping or spraying. 



Although many different types of glazes have been introduced, ice — 

 the first one used — is still the only glaze of commercial importance. 



Many patents have been issued describing the addition of various 

 chemicals to water to reduce the brittleness or evaporation of the ice 



