88 Condensed Milk and Milk Powder 



which the milk is subjected. The milk passes from the center to the 

 periphery of the discs. While being forced through the discs the 

 fat globules are split up very finely. The discs- used in this machine 

 are of two types. One type has very fine irregular grooves. The 

 milk shoots through these grooves against hard shoulders. The 

 other type of discs has smooth surfaces but their area of contact is 

 narrow. The milk passes through between these smooth surfaces. 

 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 in- 

 gredients of milk. 



Operation of the Homogenizer. — In order to avoid fat separa- 

 tion it is necessary to reduce the fat globules to about one-third their 

 original size. If enough pressure is applied to divide the fat glob- 

 ules much smaller, there is a tendency to also change the properties 

 of the casein; causing 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 disas- 

 trous than the original defect. Great care must, therefore, be exer- 

 cised, guarding against the use of excessive pressure that would in- 

 jure the casein. Experiments have shown that a pressure of be- 

 tween seven hundred and one thousand pounds per square inch is 

 sufficient to prevent fat separation and is practically harmless as 

 far as its 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 returned 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, run- 

 ning water through it, until most of the remnants of evaporated 

 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 contamination, infecting the 

 evaporated milk with spore forms that are exceedingly resistant and 



