232 SWEETENED CONDENSED MILK 



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 thickening. 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 milk, 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 



