April 1951 COmERCLAL FISHERIES REVIEW 23 



oxidize to such a small extent that they usually can be held without serious deteri- 

 oration for at least nine months. Pink salmon are seldom cut into fillets or other 

 dressed forms and then frozen. Since their storage life is of an exceedingly short 

 period, they cannot be marketed before becoming inedible. When pink salmon are 

 stored round and if protected adequately by an ice glaze, they can be stored for 

 about six months before evidences of rancidity and oxidation become pronoimced. 



Most of these changes due to oxidation can be minimized by using good handling 

 practices during cold storage. One of the best ways to minimize these changes is 

 to hold the fish at as low a temperature as possible. Fish stored at 0° F. will keep 

 more than twice as long as fish stored at 20° F, In addition to the use of low stor- 

 age temperatures, it is Important to protect the fish in such a way that oxygenfrom 

 the air does not reach the meat or oil. For whole fish, this is best accomplished 

 by providing a good ice glaze of sufficient thickness when the fish are first put 

 in cold storage. If such fish are held for a sufficiently long period, the ice 

 glaze may disappear by evaporation. In such cases, it is iii5)ortant to replace the 

 glaze before it has disappeared by re-glazing or spraying the fish if they are to 

 be held for any extended period of time. The ice glaze should be applied immedi- 

 ately after the fish have been con^jletely frozen. 



CHANGES CAUSED BY FREEZING 



When fish are canned, usually a small part of the protein rises to the surface 

 of the can and coagulates to form a white substance resembling egg white, commonly 

 known as curd. Ordinarily, this ciird forms in such a small quantity as to be un.- 

 noticaable. Frozen fish have a tendency to form more ciu-d than fresh fish. Appar- 

 ently the freezing process causes a certain amount of denaturation which gives a 

 product more curd than would be the oase if the fish had not been frozen. 



The curd is more objectionable in canned fish when the main bulk of the fish 

 has a bright color, contrasting sharply with the white color of the curd. Thus, 

 chum salmon, which have a very light color, even without the curd, are not seriously 

 impaired even with a considerable quantity of curd. 'iJhen fish having a bright red 

 color (such as chinook or sockeye salmon) are canned, there is a marked contrast be- 

 tween the color of the curd and the color of the canned fish, A small amount of 

 curd formed with such fish will be readily noticed and may detract considerably 

 from the appearance of the canned product. Accordingly, the increase in curd for- 

 mation brought about by canning frozen fish is a less serious problem with chum 

 and pink salmon than it is with the other species, especially when the fish have 

 been stored for only a short period of time. When salmon stored in the frozen state 

 for several months are canned, the curd will be dark and discolored, and this is 

 objectionable for all species. 



All salmon contain a certain amDunt of body oils, the amoiont varying from a 

 very small percent in the case of chum salmon to more than 10 percent of the weight 

 of king and sockeye salmon. Ordinarily, this oil is dispersed throughout the fresh 

 or frozen salmon. When salmon is canmed, however, some of the oil is released from 

 its combination with the tissues of the fish and works its way to the top of the 

 canned fish. It can be noted that there is a certain amount of moisture mixed with 

 oil at the surface of an opened can. This oil, idiich is known as free oil, repre- 

 sents only a part of the oil in the can since most of it is still combined in the 

 tissue of the fish. Fish which contain only a small percentage of oil in the meat 

 will give a very small amount of free oil, whereas the more oily species, such as 

 Chinook and sockeye, yield a very appreciable amount of free oil. 



In certain markets the presence of free oil is considered as giving the canned 

 salmon a premium value, and fish which have less than the average amoimt of oil 



