Evaporated Milk — Homogenizing 113 



The Progress homogenizer is used in numerous evaporated 

 milk factories in this country and, where operated properly, it 

 overcomes fat separation very satisfactorily, without damaging 

 the other ingredients of milk. 



Operation of the Homogenizer. — In order to avoid fat 

 separation it is necessary to subject the milk to enough pressure 

 to reduce the fat globules to about one-third their original size. 

 If enough pressure is applied to divide the fat globules into 

 much smaller units there is a tendency to also change the prop- 

 erties of the casein to such an extent as to cause it to give rise 

 to copious precipitation, when the evaporated milk is sterilized, 

 and making the finished product curdy and unmarketable. In 

 this case the cure would be more disastrous than the original 

 defect. Great care must, therefore, be exercised, guarding 

 against the use of excessive pressure that would injure the 

 casein. Experiments have shown that a pressure of between 

 one thousand and fifteen hundred pounds per square inch is 

 sufficient to prevent fat separation and is practically harmless 

 as far as its objectionable effect on the casein in the evaporated 

 milk is concerned.. 



The evaporated milk is run through the homogenizer hot, 

 just as it comes from the vacuum pan or standardizing tank. The 

 first pailful of milk passing through the machine should be re- 

 turned to the supply tank, as on the start, the pressure is not 

 uniform and homogenization is incomplete. 



The pistons, cylinders, valves and pipes of the homogenizer 

 should be kept in sanitary condition. They are difficult to clean. 

 After homogenizing, the machine should be kept in operation, 

 running water through it, until most of the remnants of evap- 

 orated milk are rinsed out; then hot water containing some 

 active alkali should be pumped through ; this should be followed 

 by clean hot water and steam. Unless this machine is kept 

 scrupulously clean, it may become a dangerous source of con- 

 tamination, infecting the evaporated milk with spore forms that 

 are exceedingly resistant and which are liable to pass into the 

 finished product alive, in spite of the sterilizing process, causing 

 the goods to be a complete loss, due to subsequent fermenta- 

 tion. 



