CANNING OF FISH AND FISH PRODUCTS 435 



are usually labeled by automatic machinery which operates very rapidly. The 

 three common sizes of salmon cans are the 1-pound tall, 1-pound flat, and ?2-pound 

 flat. A small amount of salmon is put up on the Columbia River in 1-pound oval 

 and /2-pound oval cans. Salmon are usually marketed in cases containing 48 

 one-pound, or 48 one-half-pound cans; sometimes 96 one-half-pound cans are put 

 in larger cases. 



The scientific and local names for the 5 species of Pacific salmon are given in 

 Chapter 10. 



The Canned Product. Grades. The principal grading of salmon is by species 

 and locality. On the Columbia River an attempt is made to separate the chinook 

 salmon into three grades on the basis of color and the amount of oil on top of 

 the can, but very little has been done toward grading the other species. Grading 

 by species and locality is unsatisfactory and frequently very unjust. A system based 

 on certain qualities which are uniform for all localities is much needed. 



Physical Examination. The quality of canned salmon may be determined from 

 3 standpoints: (1) the workmanship in packing, (2) the quality of the fish when 

 caught, and (3) the condition of the fish when packed. Of these the last, of 

 course, is the most important. 



Well-packed cans should have a good vacuum, from 8 to 12 inches, and should 

 be well filled. The fish should be well cleaned and cooked sufficiently to render 

 the bones soft and easily friable. There should be a definite salty flavor. 



The quality of the fish when caught may be determined by the amount of 

 free oil, the color of the flesh, and the presence or absence of characteristic skin 

 markings which develop as the fish deteriorate during the spawning migration. 



The condition of the fish when packed is judged by certain physical signs in 

 the canned product. Among these are odor, the appearance of an unnatural red- 

 dening of the flesh, "honeycombing," texture, and turbidity of the liquor. Canned 

 salmon of doubtful quality, judged by odor or appearance, may be examined 

 chemically for indol and skatol and for hydrogen or other decomposition products. 



Bacteriological Exainitmtioii. A suitable percentage of the cans should be ex- 

 amined for living organisms. For this purpose they are carefully cleaned, the tops 

 sterilized, and a part of the contents transferred to suitable media. If any micro- 

 organisms are found, they are studied further in order to determine the general 

 group to which they belong. In this manner it is often possible to tell whether 

 further spoilage will occur, whether the organisms gained entrance through poorly 

 made seams, or whether they resisted the processing temperature. 



Chemical Composition. Clark and Shostrom have analyzed nearly 800 cans of 

 salmon, representing the 5 species of Pacific salmon and the steelhead ti'out from 

 every important salmon-canning district from northern California to the Yukon 

 River, Alaska. Most of the cans of salmon analyzed were prepared from the second 

 cut of an individual fish. This was done because the composition varies in different 

 parts of the fish, and cans from the same part may be compared better than 

 those from different parts. A summary of the results obtained by Clark and 

 Shostrom is given in Tables 94 and 95 (p. 436) . 



The food value of salmon depends almost entirely upon protein and fat. The 

 amount of protein in the 5 species does not differ very much, and from a tissue- 

 building standpoint one is about as good as another. The amount of fat differs 



