UNSWEETENED CONDENSED MILK DEFECTS 



267 



nishes the chief source of contamination of the milk, though it 

 is quite possible that contamination with these germs may also 

 result from the use of unclean equipment in the factory. 



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 



Fig. 88. The result of gaseous 

 fermentation 



Fig*. 89. Flectridium foetidum, 

 a highly resistant species of 

 anaerobic micro-organisms, 

 causing- "swell heads" of 

 evaporated milk 



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 

 temperatures, 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 

 affected by the freezing process, the remelted evaporated milk 

 is usually less smooth and often slightly grainy. This is due to 

 the fact that, during the process of freezing, there is a partial 

 separation of the watery portion from the caseous material. The 

 casein contracts and the watery portion freezes. When melted, 

 the emulsion is less complete than it was before freezing. The 



