244 SWEETENED CoNDENSED Mik DEFECTS 
the fresh milk is subjected in the forewarmers and before it 
reaches the vacuum pan. The thermal death point of all forms 
of yeast which have come to the attention of the writer in con- 
nection with a vast number of investigations of fermented con- 
densed milk was below 180 degrees F. If all the milk is properly 
heated in the forewarmers to 190 degrees I. or over, there is, 
therefore, little danger of fermented milk, caused by contamina- 
tion of the fresh milk on the farm with yeast. If, however, the 
heating is incomplete, or if some of the milk passes into the 
vacuum pan without having been properly heated, there is dan- 
ger of milk, contaminated with these yeasts, to result in fer- 
mented condensed milk. 
Contamination with Yeast in the Factory.—As previously 
stated, yeast fermentation of condensed milk can almost  in- 
-) Fig. 86. Yeast cells causing 
2 gaseous fermentation 
sass a mail 
eae This species is capable of 
Fig. 85. Gaseous fermentation in fermenting sugar solutions 
sweetened condensed milk! containing 85% sucrose.? 
variably be traced back to contamination in the factory. After 
the milk leaves the forewarmers, or hot wells, it is never again 
heated to temperatures high enough to destroy these destructive 
yeast cells. The channels through which yeast contamination 
may occur in the factory are many. 
1 Hunziker, A Study of the Causes of Fermented Sweetened Condensed 
Milk, 1910. 
