540 MICROBIOLOGY OF FOODS 



of which the market affords several types. These operate on the same 

 principle as the laboratory autoclav or the commercial canner's retort. 



SPOILAGE OF CANNED FOODS 



MICROBIAL changes occur when the goods have not been proc- 

 essed at a temperature sufficiently high to destroy all the organisms 

 present in the uncooked food, or when a vacuum has not been estab- 

 lished. In some instances, the organisms decompose the contents of 

 the can with formation of gas, causing bulging of the ends of the cans 

 sometimes to the point of bursting at the seams. Such cans are desig- 

 nated at the factory as "swells." In other instances, the bacteria 

 cause an acid fermentation with consequent souring of the contents. 

 The canner terms such cans "flat sours." 



DETECTION OF SPOILED GOODS. In cases of spoilage accompanied 

 by gas production, detection of the spoiled cans is easy from the 

 bulged appearance of the ends of the cans. On account of the exhaus- 

 tion of air from the cans previous to processing, the ends of sound cans 

 should be slightly concave. If the ends of the cans are convex, it 

 indicates some abnormal condition of the contents and such cans should 

 be rejected. In the case of sours, detection is not so easy. The can 

 may appear normal, and there may be no change in the contents appar- 

 ent to the eye on opening the can. Taste, however, reveals a more or 

 less pronounced disagreeable acid flavor. Canned meats, fish, or crus- 

 taceans are likewise liable to spoilage if the processing has been imper- 

 fectly carried out. In these goods the change is generally accompanied 

 by gas production, hence detection is easy because of the swelled 

 appearance of the cans. 



If gas production is present, or there is an odor resembling rancid 

 cheese, or if the contents appear mushy or disintegrated, in no case 

 should the contents of the can be tasted to see if it is spoiled, as these 

 conditions indicate spoilage by B. botulinus, and the toxin of this 

 organism may prove fatal in the smallest traces. 



DISPOSAL OF FACTORY REFUSE 



The disposal of factory refuse has at times been a serious problem for the 

 commercial canner. Of late years methods have been devised for utilizing much 

 of the material that formerly was allowed to accumulate about the factory 

 in fermenting heaps to the extent of sometimes becoming a nuisance to the neigh- 

 borhood. 



