SWEETENED CONDENSED MILK DEFECTS 209 



contain traces of invert sugar, or acid, etc., many of these com- 

 mon species of micro-organisms, harmless in normal condensed 

 milk, find an opportunity to develop and cause gaseous fermenta- 

 tion. The presence of invert sugar makes unnecessary the action 

 of invertase in order to start fermentation ; thus, microbes which 

 do not secrete invertase and are otherwise harmless, may become 

 detrimental in the presence of invert sugar, added to the milk 

 in the form of a poor quality of cane sugar. In a similar way 

 the use in condensed milk of commercial glucose, as a substitute 

 of a part of the cane sugar, and in order to reduce the cost of 

 manufacture, is bound to cause disastrous results. Nothing but 

 the best refined, granulated sucrose should be used, the best is 

 the cheapest. 



Dangerous Effect of High Acid in Milk. Acids have the 

 power of inverting sucrose. The inversion by acid is especially 

 active in the presence of heat. The milk in the vacuum pan is 

 condensing at 130 to 150 degrees F. These temperatures are 

 most favorable to inversion of a portion of the sucrose in the 

 presence of acid. The higher the acid content of the milk, the 

 more active is the inversion. Since invert sugar is the very 

 ingredient necessary to cause bacterial action in the finished 

 product, it is essential that the acidity of the milk to be con- 

 densed, should be held down to the minimum in order to avoid 

 trouble from this source. 



Contamination with Butyric Acid Bacteria. Frequently the 

 troublesome microbe is not a yeast, but belongs to a species of 

 bacteria highly resistent to heat, and which fail to be destroyed 

 by heating the milk to the boiling point. In this case, the con- 

 tamination usually originates on the farm. Organisms of this 

 kind, which infest the milk on the farm in this connection, largely 

 belong to the butyric acid group. The most prominent among 

 them are Granulobacillus saccharo-butyricus mobilis or Bacillus 

 saccharobutyricus, Bacillus esterificans, Bacillus dimorphobuty- 

 ricus. The putrefactive forms of butyric acid organisms, such as 

 Bacillus putrificus, Plectridium foetidum, Plectridium novum, 

 etc., do not seem to thrive in sweetened condensed milk. 



The contamination may occur from dust of hay and other 

 fodder, grain, bedding, or the unclean coat of the udder and sur- 



