172 Condensed Milk and Milk Powder 



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 subse- 

 quent contamination of the contents of the cans with these germs, 

 and the only possible channel, through which this subsequent con- 

 tamination 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 mix- 

 ture 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 anae- 

 robes, 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 suggests 

 incomplete sterilization of the evaporated milk. The striking white- 

 ness of the curd in all cases that have come to the writer's attention, 

 is further proof of the correctness of this deduction. It indicates 

 that these cans received relatively little heat in the sterilizer, other- 

 wise the curd would have a darker color. This defect usually does 

 not show up in all the cans of one and the same batch, but only in a 



