Condensed Milk and Milk Powder 



175 



Plectridium foetidum, as well as most of the other species of 

 anaerobic, spore bearing butyric acid bacilli and bacteria, is present 

 abundantly in cultivated soil, in field crops and even on the kernels 

 of the grain. Since this type of evaporated milk defect is charac- 

 teristic, especially, of the product manufactured during the late sum- 

 mer and early fall months, it is very probable that the dust incident 

 to the harvesting of the field crops, furnishes the chief source of 

 contamination of the milk. 



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Fig., 52. The result of gaseous fermentation 



Fig. 53. Plectridium foetidum, a 

 highly resistant species of anaerobic 

 microorganisms, causing "swell heads" 

 of evaporated milk 



In order to avoid the occurrence of blown, fermented, evapo- 

 rated milk, therefore, it is necessary to employ the highest sterilizing 

 temperatures, or the longest exposure to the sterilizing heat, or both, 

 consistent with freedom of the milk from curdiness. Experience has 

 shown that the use of the formula for sterilizing, given under Chap- 

 ter XII on "Sterilizing," guards effectively against this defect. 



Blown Evaporated Milk Due to Freezing. — If the evaporated 

 milk is exposed to storage temperatures below the freezing point 

 of water, the contents of the cans will freeze. While freezing, the 

 contents expand sufficiently to cause the ends of the cans to bulge. 

 When the cans are subsequently transferred to warmer temper- 

 atures, so that their contents melt again, the milk contracts and the 

 cans resume their normal shape. 



While the wholesomeness and flavor of the product are not af- 

 fected by the freezing process, the remelted evaporated milk is usu- 

 ally less smooth and often slightly grainy. This is due to the fact 



