Unsweetened Condensed Milk Defects 223 



General Description. — Upon opening the cans the contents 

 are found to be sour and curdy. 



Causes and Prevention. — This condition is the result of the 

 presence of acid producing species of micro-organisms, usually 

 of the lactic acid type, which sour the milk, and the acid produced 

 curdles the casein. Since the majority of the lactic acid bacteria 

 are not resistant to heat and are destroyed at relatively low heat, 

 this defect is not usually caused by incomplete sterilization. The 

 temperature of sterilization, though it might be insufficient to 

 kill spore forms, is high enough to make it impossible for lactic 

 acid bacteria to pass the process alive. 



The only way in which this defect can occur is through sub- 

 sequent contamination of the contents of the cans with these 

 germs, and the only possible channel, through which this sub- 

 sequent contamination may occur, is leaky cans, or leaky seals. 

 A careful examination of the cans of sour, curdled evaporated 

 milk usually shows faulty cans or faulty seals. 



Bitter Curd 



General Description. — When the cans are opened the con- 

 tents present a solid coagulum, generally noticeably white in 

 color and very bitter to the taste, similar to the bitterness of 

 dandelions. There is a separation of practically clear whey, the 

 curd does not break down readily upon shaking and the acid 

 reaction of the mixture of curd and whey is about .35 to .40 per 

 cent., which is normal for evaporated milk. 



Causes and Prevention. — Microscopic examinations under 

 high magnification of cultures in sterile milk show the presence 

 of very small bacilli. The milk forms a firm coagulum in five to 

 seven days and when over one week old the curd has the same 

 strong, bitter taste as that in the cans. The bitterness increases 

 with age. These bacilli grow best at 90 degrees P. They are 

 facultative anaerobes, developing both, in aerobic and anaerobic 

 media, but prefer anaerobic conditions. 



In the cases under observation no spores were detected and 

 exposure for fifteen minutes to 212 degrees F. destroyed these 

 germs. The above findings do not exclude the possibility of spore 

 formation under conditions very unfavorable to growth and life. 



The presence of this species of bitter curd organisms sug- 

 gests incomplete sterilization of the evaporated milk. The strik- 



