UNSWEETENED CoNDENSED Mink 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 cecurrence 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. 89. Plectridium foetidum, 
a highly resistant species of 
= anaerobic micro-organisms, 
Fig. 88. The result of gaseous causing “swell heads” of 
fermentation evaporated milk 
time of exposure, given under Chapter XI on “Sterilizing.” guard 
effectively against this defect. 
Blown Evaporated Milk Due to Freezing.—lf the evapo- 
rated milk is exposed to storage temperatures below the freezing 
point of water, the contents of the cans will freeze. \While freez- 
ine, 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 smeoth 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 
easein contracts and the watery portion freezes. \Vhen melted, 
the emulsion is less complete than it was before freezing, ‘The 
pie 
