226 



UNSWEETENED CONDENSED MILK DEFECTS 



yellow liquid, similar in appearance to butter oil. The fermenta- 

 tion is accompanied by the evolution of a penetrating foul odor. 

 This organism survives exposure for 15 minutes to 245 degrees 

 F. Its thermal -death point lies between 245 and 250 degrees F. 

 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 characteristic, especially, of the product manufactured 

 during the late summer and early fall months, it is very probable 

 that the dust incident to the harvesting of the field crops, fur- 

 nishes the chief source of contamination of the milk. 



Fig. 56. The result of gas- 

 eous fermentation 



Fig. 57. Plectridium foetidum, a 

 highly resistant species of an- 

 aerobic microorganisms, caus- 

 ing "swell heads" of evapo- 

 rated milk 



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

 rated milk, therefore, it is necessary to employ the highest steriliz- 

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

 or both, consistent with freedom of the milk from curdiness. Ex- 

 perience has shown that the use of the ranges of temperature and 

 time of exposure, given under Chapter XI on "Sterilizing," guard 

 effectively against this defect. 



Blown Evaporated Milk Due to Freezing. If the evapo- 

 rated milk is exposed to storage temperatures below the freezing 

 point of water, the contents of the cans will freeze. While freez- 

 ing, the contents expand sufficiently to cause the ends of the cans 

 to bulge. When the cans are subsequently transferred to warmer 



