154 Condensed Milk and Milk Powder 



lumps from this source, cans should be used, in the manufacture of 

 which a strictly acid-free flux is used and which are sealed with 

 acid-free flux. Dry, powdered resin or resin dissolved in alcohol or 

 gasoline are harmless in this respect and are just as effective fluxes, 

 as acid flux. 



Unclean and Contaminated Tin Cans. — Finally, there frequently 

 appear in sweetened condensed milk, species of lumps which are 

 firm and cheesy and which usually float on top of the milk in the 

 can. These are called buttons. Some are white, others are yellow. 

 These buttons appear in old milk more frequently than in milk that 

 has been in storage for a short time only. They grow in size and 

 sometimes one "button" covers the entire surface of the condensed 

 milk in the can. Their origin is not well understood, but they are 

 supposed to be the result of fungus growth. It is not improbable 

 that they are produced by molds, the spores of which gain access to 

 the condensed milk in the factory, or to the cans before they are 

 filled. These "buttons" appear in the canned goods and in the 

 barrel goods. Their occurrence can be minimized by protecting 

 the condensed milk and the empty cans from dust and other im- 

 purities or by sterilizing the cans immediately before use, and by 

 paraffining and thoroughly steaming the barrels before filling. 



Blown, or Fermented Sweetened Condensed Milk 



. General Description. — One of the most disastrous tr.oubles 

 in the manufacture of sweetened condensed milk is the appearance 

 of "swell heads." This term is applied to cans of condensed milk, 

 the contents of which have undergone gaseous fermentation, 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 formation of lumps. 



This fermented milk is worthless for any purpose and means 

 a total loss to the manufacturer. The loss is generally augmented 

 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 repu- 



