236 SWEETENED CONDENSED MiiyK DEFECTS 



stances which are highly sensitive to heat, such as albumin, 

 colostrum, etc. 



Excess of Acid in Condensed Milk and Acid Flux in Tin 

 Cans. The presence in the condensed milk of organic and 

 mineral acids, in excess of the amount which normal fresh milk 

 contains, is conducive of the formation of lumps. 



Excessive amounts of acid in condensed milk may be the 

 result of fermentations, usually due to a poor quality of sugar, 

 or of the use of acid flux in the making and sealing of the tin 

 cans. Condensed milk that shows acid or gaseous fermentation 

 usually contains lumps. The acid which it develops as the result 

 of the fermentation, curdles the casein with which it comes in 

 contact. 



One of the most common channels through which condensed 

 milk may become contaminated with acid mechanically, is the 

 use of cans, in the manufacture and sealing of which acid flux 

 was used. The acid flux generally used contains zinc chloride. 

 The flux precedes the solder and some of it is bound to sweat 

 through the seams into the interior of the cans. This type of 

 lumps usually has a pink or brownish-red color, especially in the 

 case of considerable quantities of acid flux. Zinc chloride is a 

 highly poisonous 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 effect on the 

 health and life of the consumer, its presence, even in small quan- 

 tities in condensed milk, is a detriment to its market value. In 

 such cans there accumulate, usully along the seams, lumps and 

 smeary substances 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 the appearance in con- 

 densed milk of 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. 



