206 SWEETENED CONDENSED MILK 



sugar solution of this product. Contamination of the condensed 

 milk with these specific organisms is usually the result of highly 

 unsanitary conditions in the handling of the condensed milk. 



The products of fermentation depend on the particular type 

 and species of micro-organisms involved. In most cases the 

 sucrose is the chief constituent attacked, but the lactose, also, 

 is capable of gaseous fermentation, though instances of lactose 

 fermentation in sweetened condensed milk are not common. 



The gaseous fermentation, of lactose is largely caused by 

 bacteria, yeast and molds which contain the lactose-splitting 

 enzyme "lactase," which has the power of hydrolyzing the lac- 

 tose. While the species of organisms which cause lactic acid 

 fermentation from lactose are very numerous, those containing 

 the enzyme lactase and thereby causing gaseous fermentation 

 from lactose, are less frequent, at least, as far as their access to 

 milk and condensed milk is concerned. It is generally under- 

 stood, though not experimentally proven, that species of micro- 

 organisms which do not contain the enzyme lactase have no gas- 

 producing action on lactose. 



The great majority of cases of gaseous fermentation of 

 sweetened condensed milk are the result of the action of micro- 

 organisms on the sucrose, especially tho>se which contain the 

 enzyme "invertase." The majority of yeasts secrete invertase 

 and ferment sucrose, producing alcohol and carbon dioxide to 

 the same extent as in the case of glucose fermentations. The 

 process is considerably slower, however, especially at the start, 

 owing to the fact that inversion of the sucrose must precede 

 fermentation. For this reason gaseous fermentations of sweet- 

 ened condensed milk do not become noticeable until the product 

 is one or several weeks old. 



Contamination With Yeast on the Farm. In most cases of 

 yeast fermentations of sweetened condensed milk, the source of 

 contamination lies in the factory. While such contamination 

 may and often does occur on the farm, the yeast cells, though 

 they may be spore-bearing, are destroyed by the heat to which 

 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- 



