CANNING OF FISH AND FISH PRODUCTS 437 



from protein, they are often formed in decomposing salmon flesh. Skatol is rarely 

 formed, probably because few bacteria are able to produce it. Only one such 

 organism has been isolated by Fellers, whereas no less than 30 per cent of all 

 cultures examined from decomposed salmon was able to produce indol from salmon 

 flesh. 



No pathogenic species of bacteria has been isolated from over 600 cultures 

 from raw and canned salmon. The time and temperature of the process employed 

 in canning salmon precludes the possibility of survival of dangerous bacteria, such 

 as C. botulinum or organisms capable of causing gastrointestinal disturbances, 

 unless the cans are accidentally underprocessed. The heat penetration in salmon 

 during the processing has been carefully studied in the Seattle Laboratory of the 

 National Canners Association, and it has been found that the usual process of 90 

 minutes at 242° F (117° C) is sufficient for preserving the canned product from 

 future spoilage, for eliminating any dangerous organisms that might have been 

 present in the raw product, and for thoroughly cooking the fish and softening the 

 bones. 



In the manufacturing process for cans the canning methods and processing 

 times have been brought to such a state of perfection that less than 2 per cent of 

 the pack is found to be defective. The living bacteria which are now found 

 in canned salmon are mainly aerobic spore-formers, such as B. vulgatus, B. mesen- 

 tericus, B. cereus, B. subtilis, and similar species. These are harmless saprophytes 

 and are the common bacteria of dust and soil. The source of these organisms is 

 believed to be the dust in unwashed empty cans since bacteria of this type are not 

 commonly associated with fresh salmon. This theory has been partially confirmed 

 and is now being studied further. 



The "exhaust box" in the cannery creates a vacuum in the cans. The vacuum 

 inhibits to some degree the aerobic species of bacteria from developing in well- 

 exhausted cans of salmon. It has also been found that the gaseous oxygen in the 

 can disappears in a few days and is probably held in combination by the con- 

 tents, thus eliminating the free oxygen remaining after the exhaust. The aerobic, 

 spore-forming bacteria, such as those occasionally found alive in canned salmon, 

 do not produce gas (i.e., swells); although some growth may result, in general no 

 serious spoilage takes place. A few cases have been encountered in the trade 

 where the presence of these species in large numbers materially reduced the grade 

 and market price of the product, though little or no decomposition could be 

 detected by ordinary methods. 



Thermophilic bacteria are not common in canned salmon, though a few species 

 have been isolated. A good vacuum in the can effectively prevents further growth 

 of some species of thermophiles. Strict putrefactive anaerobes are also uncommon 

 and are seldom encountered unless the can has a "leak" or has been under- 

 processed. Furthermore, most species of anaerobes are prolific gas-formers and 

 cause swells. These manifest themselves within a short time after processing, and 

 swells of this nature are usually discarded at the cannery. 



Sardine-Canning Industry 



All sardines, according to the generally accepted definition, are small fish of 

 the herring family. In California the variety used is the California sardine 

 {Sardinops caerulea); in Maine, the sea herring {Clupea harengus); in France and 



