292 PRESERVATION METHODS 



Fast or quick freezing is in wide usage because of its practical advantages 

 in expeditiously mass producing frozen seafood. Slow freezing is still used 

 for large whole fish such as halibut, tuna, or salmon, and no ill effects have 

 resulted because of the rate of freezing. 



The method of freezing may affect the appearance or quality of the 

 frozen product. In sharp freezing, w^here the product is frozen on refrig- 

 erated grids or plates, bulging or voids may occur because of the lack of 

 outside pressure to control product expansion. Freezing in an air blast 

 can result in excessive ''freezer burn,'' or dehydration, because of low 

 relative humidity or the use of air velocities of over 500 feet per minute 

 with unpackaged or inadequately packaged products. The package will 

 also be distorted unless devices are used to control expansion. In immer- 

 sion freezing, the temperature of the freezing medium and the time of 

 product immersion must be precisely controlled. If this is not done, the 

 immersion solution will penetrate into the fish and may adversely affect 

 the quality of the product. Products frozen in a contact-plate freezer 

 contain a minimum amount of bulges and voids and are usually highly 

 acceptable. 



Temperature. Temperature and time of storage are the most important 

 factors influencing the quality of frozen seafood. Exposure of the food to 

 higher temperatures significantly increases the rate of quality loss. Like- 

 wise, a reduction in product temperature retards the adverse quality 

 changes that take place in the frozen state and results in an extension of 

 product shelf life. 



It may be said that fresh frozen seafood contains a fixed amount of 

 edible quality, the loss of which is both temperature and time dependent. 

 The product will lose this quality over a rather long period of time when 

 stored at low temperatures and over a proportionally shorter period of 

 time when subjected to high temperatures. Van Arsdel, et al.,"^^ have used 

 a time-temperature coordinate system to mathematically estimate the 

 quality loss of frozen fruits and vegetables subjected to a number of dif- 

 ferent temperatures for various periods of time. Slavin^^ reported that 

 this tool shows considerable promise in estimating the loss of quality in 

 frozen fishery products. 



IVIany investigations conducted on the storage of frozen fishery prod- 

 ucts verify that a decrease in product temperature markedly reduces loss 

 of quality, Notevarp and Heen^^ and Reay^^ found a great difference in 

 the quality of fish stored for only several weeks at 14 and — 4°F. Dyer, 

 ei al.,^^ found that frozen rose fish fillets can be kept in good condition for 

 4 to 5 months when stored at 10°F and for 6 to 8 months when stored at 

 — 10°F. It was also reported that frozen cod stored at temperatures of 

 15°F for only 3 to 14 days will deteriorate in quality quite rapidly '^ 



