Condensed Miek and Miek Powder 149 



gins some days and often some weeks after manufacture and in- 

 creases as the milk grows older. 



Effect of Cow's Feed on Thickening. — Again, the cause of this 

 defect has been attributed to the change in feed, the cows being 

 turned from dry to succulent feed at the time when this tendency 

 of the condensed milk to thicken occurs. There is no reliable evi- 

 dence, however, of how the succulent pasture 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 fermen- 

 tation 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 during 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 usu- 

 ally 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 con- 

 tains, the bacteria in it increase with the age of the milk. The 

 thickening of the sweetened condensed milk in early summer, there- 

 fore, 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 me- 

 dium for bacterial growth. Furthermore, it has been conclusively 

 demonstrated by the writer and others that the addition of cane su- 

 gar 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-produc- 

 ing bacteria, 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 



