HEAT IN THE PRESERVATION OF FOOD PRODUCTS. 393 



being hardly noticeable in two or three years, and the change will be even 

 more gradual at a low temperature. 



SPOLIATION OF PASTEURIZED AND STERILIZED GOODS. 



CHEMICAL. Aside from the change just mentioned, the chief chemical 

 action is that of the fruit acids on the tin containers, with consequent 

 formation of poisonous salts of lead or tin. The use of enamelled cans, 

 however, effectually prevents electrolysis from the action of the fruit acids 

 on the tin with impairment of color of the product, and also prevents 

 formation of lead or tin salts. 



A kind of spoilage which sometimes occurs in goods packed with the 

 seeds or with the pits, and which causes a bulging of the ends of the cans, 

 designated by the canner as " springers" or " flippers," is caused by 

 insufficient heat being applied during the processing to destroy the germ 

 of the seed. 



MICROBIOLOGICAL changes occur when the goods have not been 

 processed at a temperature sufficiently high to destroy all microorganisms 

 which may have been present in the uncooked product. In some in- 

 stances, the organisms present decompose the contents of the can, with the 

 formation of gas, causing bulging of the cans, sometimes to the point of 

 bursting at the seams. Such cans are designated at the factory as " swells" 

 in distinction from the springers mentioned above. In other instances 

 the bacteria in the imperfectly sterilized cans produce an acid fermenta- 

 tion, with consequent souring of the contents. Such cans are termed 

 "sours" by the canner. 



Spoilage may occasion great monetary loss, as sometimes a whole 

 season's pack may be lost. 



DETECTION or SPOILED GOODS. In cases of spoilage accompanied 

 with gas production, detection of the spoiled cans is usually easy, from 

 the swelled appearance of the can. On account of the exhaustion of air 

 from the cans during processing, the ends of sound cans should be slightly 

 concave. If, then, 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 apparent to the eye 

 on opening the can. Taste, however, reveals a more or less pronounced 

 disagreeable acid flavor. 



