Condensed Milk and Mii,k Powder 155 



tation of the respective brand is jeopardized. In some instances 

 entire batches show this defect, while in others only a few cans or 

 cases of each batch are blown. 



Causes and Prevention. — This defect may be brought about 

 through various channels. In most cases it is due to contamination 

 of the milk, on the farm or in the factory, with specific micro- 

 organisms which are capable of fermenting one or more of its 

 ingredients, in spite of the preservative action of the sucrose; or 

 the condensed milk may contain highly fermentable substances such 

 as glucose or invert sugar, so that the germs normally present in 

 the condensed milk become active and produce gas ; or the milk 

 may not be condensed to a sufficient degree of concentration, or may 

 not contain adequate quantities of sucrose, to render it immune to 

 the bacteria normally present. The cans may also bulge without 

 bacterial action, as the result of exposure to a wide range of tem- 

 peratures, causing mechanical contraction and expansion of the 

 contents. 



Contamination With Specific, Gas-Producing Bacteria and 

 Yeast. — This is by far the most common cause of blown milk. While 

 the micro-organisms which, under normally sanitary production of 

 milk and factory conditions, gain access to the condensed milk, are 

 largely inhibited and do not ferment the sweetened condensed milk, 

 there are certain specific forms of bacteria and yeast whose growth 

 is not retarded by the concentrated 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 oi 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 bac- 

 teria, yeast and molds which contain the lactose-splitting enzyme 

 "lactase," which has the power of hydrolyzing the lactose. 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 fre- 

 quent, at least, as far as their access to milk and condensed milk is 



