204 Sweetened Condensed Milk Defects 



seams into the interior of the cans. Zinc chloride is a highly poi- 

 sonous product and its use in the manufacture of tin cans, which 

 are intended for receptacles of human food, should be prohibited 

 by law. Aside from its injurious efifect on the health and life of the 

 consumer, its presence, even in small quantities in condensed 

 milk, is a detriment to its market value. In such cans there 

 accumulate, usually along the seams, lumps and smeary sub- 

 stances which have been found to consist of casinate of zinc. 



Most commercial soldering fluxes consist largely of zinc 

 chloride and are highly acid, although many of these are adver- 

 tised as acid-free fluxes. In order to avoid condensed milk con- 

 taining 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 fre- 

 quently 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 fre- 

 quently than in milk that has been in S;torage 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 "but- 

 tons" 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 impurities, by steriliz- 

 ing 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 troubles 

 in the manufacture of sweetened condensed milk is the appear- 

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



