242 SWEETENED CONDENSED MILK DEFECTS 



Blown, or Fermented Sweetened Condensed Milk. 



General Description. One of the most disastrous troubles 

 in the manufacture of sweetened condensed milk is the appear- 

 ance of "swell heads." This term is applied to cans of con- 

 densed milk, the contents of which have undergone gaseous fer- 

 mentation, the resulting pressure causing the ends of the cans 

 to bulge or swell, and frequently to burst open the seams. In 

 the case of barrel goods, the pressure may cause the barrel head 

 to blow out. This gaseous fermentation is usually, though not 

 always, accompanied by the development of acid and the for- 

 mation of lumps. 



This fermented milk is worthless for any purpose and means 

 a total loss to the manufacturer. The loss is generally aug- 

 mented by the fact that this trouble does not become noticeable 

 at once ; its development requires several weeks, so that large 

 quantities of condensed milk may have been manufactured before 

 it is apparent that the milk is defective. Some of the goods may 

 have reached the market before the cans begin to swell, in which 

 case the reputation, 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 contamina- 

 tion 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 pro- 

 duce 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 temperatures, 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 pro- 



