UNSWEETENED CONDENSED MILK DEFECTS 263 



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 F. 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- 

 ing whiteness of the curd in all cases that have come to the 

 writer's attention, is further proof of the correctness of this de- 

 duction. It indicates that these cans received relatively little 

 heat in the sterilizer, otherwise 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 limited portion of each 

 batch. This fact suggests that the distribution of heat in the 

 sterilizer is not uniform, some cans getting less heat than others. 



This defect occurs generally in summer, a fact which may be 

 due to one or both of the following conditions : 



While it is well known that there- is a group of species of 

 bacteria, yeast and torula that are capable of producing a bitter 

 curd, either direct, or through the secretion of casein-curdling 



