22 ♦ COMMERCIAL FISHEEilES RETIEVr Vol. 13, No. 4 



and the frozen zone gradually moves to the center. 'wDiereas the outside portion of 

 the fish may start freezing within a few minutes after the fish is placed in the 

 brine well, the center of the fish may not be frozen for 12 or more hours. During 

 the first few hours after the fish is placed in the brine well, the temperature at 

 the center of the fish may be only slightly lower than it was when the fish was 

 placed in the brine. If bacteria are present within the center of the fish, spoil- 

 age will continue for some hours after the fish is placed in the brine well. If 

 the brine well is overcrowded and inadequate refrigeration and circulation of the 

 brine is present, the length of time required for freezing the center of the fish 

 ordinarily may be extended from one-half a day to several days. Under such circum- 

 stances extensive bacterial spoilage may take place in the centers of some fish in 

 the brine well even thoiigh the fish were in prime condition when placed in the well. 

 It is extremely difficult to cull out partially spoiled fish when they are thawed 

 for canning since spoilage is present only at the center of the fish and may be 

 easily overlooked. This spoilage, moreover, is of the type that vri.ll render the 

 fish inedible and subject to seizure by the Food and Drug Administration. Hence, 

 if such fish should be canned, it is necessary to open the entire pack and re-proc- 

 ess those which have not spoiled, an exceedingly expensive and undesirable proce- 

 dure. 



Fortunately, this difficulty can be completely eliminated by using an adequate 

 refrigeration capacity and making certain that the system is not overloaded. If 

 this difficulty is to be eliminated, a person with the necessary technical knowledge 

 of the capacity of the equipment must be present at the time the fish are frozen. 



DETERIORATION OF FROZEN SALMON IN GOLD STORAGE 



The most important change which takes place in frozen salmon in cold storage 

 is oxidation of the oils and pigments of the fish. This is a chemical change where- 

 by oxygen from the air combines chemically with the fish oil and fish pigments to 

 form new chemical compounds which alter the flavor and appearance of the fish. The 

 color of the fish may be altered considerably. This takes place in two ways: the 

 normal pink or red color of the salmon fades to a more-or-less colorless hue as a 

 result of the oxidation of some of the pigment. An even more objectionable change 

 may take place in the oil directly beneath the skin. In some cases this oil oxidation 

 changes the color of the normal salmon hue to a dark broivn or nearly black color, 

 giving a very unsightly appearance to the canned product. Accompanying these color 

 changes are alterations in the flavor of the fish oil. The fresh oil has a bland, 

 somevfhat fishy flavor; upon oxidation, the oil acquires a sharp, penetrating flavor 

 vfhich is known as rancidity. Development of rancidity, if carried to an extreme 

 condition, makes the fish inedible. 



Changes brought about by oxidation during cold storage are further accentuated 

 by canning. Thus, fish vfhich have reached an incipient stage of oxidation and show 

 only a slight or no off-flavor after thawing and canning, may have a strong off- 

 flavor. For example, pink salmon, which appear to be in good condition after six 

 months storage at 0° F. , will yield a canned product having a definite off -flavor 

 even though the thawed fish vroxild have been of satisfactory quality had they not 

 been canned. 



The five species of salmon are not affected to the same extent by the action 

 of oxygen during cold storage. Pink salmon are by far the most prone to oxidation. 

 This species may become completely rancid within a few months of the time it is 

 placed in cold storage, whereas the other species protected only by mediocre means. 



