232 SWEETENED CONDENSED Mik DrErrEcts 
grasses on which the cows feed can bring about this thickening 
action in the condensed milk. 
Effect of Bacteria on Thickening.—A third and far more rea- 
sonable explanation is that this thickening is the result of a 
fermentation process. It is quite probable that the thickening 
of sweetened condensed milk is closely related to the sweet- 
curdling fermentation in fresh milk. The sweet-curdling of 
fresh milk is a fermentation characteristic of, and frequent dur- 
ing late spring and summer. It is caused by certain species of 
bacteria which are capable of producing a rennet-like enzyme, 
which has the power to curdle milk in the sweet state. ‘These 
bacteria are known to be closely associated with dirt and filth, 
especially from the feces, and gain access to the milk usually 
on the farms where the production and handling of milk is not 
accomplished under most sanitary conditions. 
It is further known, as the result of analyses that, in spite 
of the large per cent of cane sugar which sweetened condensed 
milk contains, the bacteria in it increase with the age of the 
milk. The thickening of the sweetened condensed milk in early 
summer, therefore, very probably is the result of a slow curdling 
of its casein, caused by enzymes which are produced by bacteria. 
It has further been demonstrated that condensed skim milk 
thickens more readily than condensed whole milk, which may be 
explained by the fact that condensed milk without butter fat 
represents a more favorable medium for bacterial growth. Fur- 
thermore, it has been conclusively demonstrated by the writer 
and others that the addition of cane sugar to condensed milk, 
in excess of that present in normal condensed milk, greatly 
retards thickcning. ‘This fact suggests that the higher per cent 
of sucrose has an inhibiting effect on the enzyme-producing bac- 
teria, and perhaps, on the action of the enzyme itself. ‘This 
condensed milk defect can be prevented entirely by using, during 
the summer months, eighteen pounds of sucrose per one hundred 
pounds of fresh mull, so that the condensed milk contains about 
45 per cent sucrose. 
Effect of Finishing in Pan With High Steam Pressure on 
Thickening.—Abnormally thick condensed milk is also the result 
of overheating the condensed milk in the vacuum pan toward 
the close of the process. ‘The batch should be finished with low 
