longer precook times than do smaller fish. Hence, it is customary to 

 grade fish according to size, placing fish of only one size grade in a 

 given cooker, and to vary the cooking time in proportion to the size 

 of fish in the cooker. This avoids overcooking the small fish in order 

 t.a sufficiently cook a few large ones. Usually fish are divided into 

 not more than three categories, large, medivun, and small. This still 

 leaves a fairly wide variation in size of fish in any cooker. Some 

 plants use more size grades which results in more uniform cooking and 

 less shrinkage losses by overcooking. Close attention to cooking time 

 and temperature also pays off in large savings of shrinkage loss. Some 

 plants run check weights on tuna in each cooker weighing fish before 

 and after precook to be certain that losses do not exceed pre-determined 

 limits. Many plants also have temperature recording instrummts on 

 each cooker to be certain that temperatures are accurately maintained. 



Tuna are precooked in most canneries at temperatures usually be- 

 tween 216° and 220° F, The time of precooking varies ivith the size 

 of fish and also from cannery to cannery. The following tabulation 

 is typical of cooking times used: 



In a few plants it was observed that there seaned to be a tendency 

 to reduce the precooking times apparently in an attanpt to increase the 

 yield of fish by not cooking out so much moisture. 



The racks and baskets used in the precookers rapidly become covered 

 with a coating of fish protein and hardened fish oil unless constant 

 effort is maintained to keep them clean. Some plants steam clean this 

 equipment after each cooking operation. The use of paper liners in the 



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