262 UNSWEETENED CONDENSED MILK DEFECTS 



the pressure and the intelligent use of the homogenizer, furnish 

 a satisfactory and reliable means to prevent fat separation. 1 



Fermented Evaporated Milk. 



General Description. Fermented evaporated milk is evap- 

 orated milk, which after sterilization, has undergone fermenta- 

 tion. The type of fermentations found in this product varies 

 with locality, season of year and factory conditions. The con- 

 tents of the cans may have soured with curd formation, or a 

 curd* may have formed without acid development, or the fer- 

 mentation may be gaseous, in which case the cans bulge, and 

 these gaseous fermentations may be accompanied by acid forma- 

 tion or by putrefactive products. In all cases of ferrnented milk 

 the product is entirely worthless. These defects are usually, 

 though not always, detected during the period of incubation. 



Fermented evaporated milk is the result, either of incomplete 

 sterilization, or of leaky cans. The causes of fermented evap- 

 orated milk differ Avith the specific type of fermentations pro- 

 duced; they will be discussed separately and as relating to the 

 respective types of fermentations. 



Acid Fermentation, Sour, Curdled, Evaporated Milk. 



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. 



1 For details on the use of homogenizer see Chapter IX on "Homogeniz- 

 ing." 



