248 SWEETENED CONDENSED MILK 



under average conditions. A higher per cent of sucrose would 

 naturally intensify the preservative action and inhibit the growth 

 of the bacteria normally present more completely ; but if enough 

 sugar were added to also inhibit the growth of and make harm- 

 less those violent gas-producing butyric acid bacteria and yeast 

 cells, which thrive in sweetened condensed milk containing 40 

 per cent sucrose, the product would be objectionable from the 

 consumer's point of view. The logical avoidance of "swell 

 heads" as the result of these undesirable germs, therefore, must 

 ever lie in prevention, rather than cure. The sanitary standard 

 of production on the farm and of the process in the factory must 

 be raised to and maintained on a level where the milk is pro- 

 tected from contamination with these micro-organisms. 



The writer 1 has isolated yeast from fermented sweetened 

 condensed milk that produced vigorous gas formation in media 

 containing as high as 85 per cent sucrose (600 grams sucrose in 

 100 cc. whey bouillon). 



Effect of Too Thin Condensed Milk. Condensed milk that 

 is too thin is, also, prone to start fermenting, since it is deficient 

 in the chief preserving agents, i. e., density and per cent of 

 sucrose. It is not safe to put goods on the market, with a ratio 

 of concentration much less than 2.5 :1, unless the amount of cane 

 added is sufficient to raise the cane sugar content of the fin- 

 ished product to 44 per cent or above. 



Effect of Excessively Low Temperatures. The cans of 

 sweetened condensed milk may also bulge in the case of cans 

 with non-hermetical seals, exposed successively to excessive cold 

 and to room temperature. In this case, the condensed milk is 

 entirely normal and unaffected, apd the bulging is the result 

 of mechanical contraction and expansion by cold and heat. This 

 is possible only where the seal of the cans is not entirely her- 

 metical. In the case of the Gebee seal with the burr cap, and 

 the McDonald seal with the friction cap, the seal is not absolutely 

 air-tight. While the pores betw'een cap and can are microscopic 

 in size, and not large enough to permit the contents from leak- 

 ing out, they are sufficient to admit air. The cans are usually 

 filled with the condensed milk at a temperature of about 70 de- 



1 Hunziker, Results not published. 



