Preservation of Milk. 115 



Clarifying milk. A much more efficient and less trou- 

 blesome means of removing the insoluble foreign par- 

 ticles from milk is to pass it through a cream separator, 

 allowing the cream and skim milk to mix in the same 

 container. The slime that collects on the wall of the 

 separator bowl is made up of dirt, casein, bacteria, and 

 the cellular debris from the interior of the udder. The 

 bacteria are heavier than the milk serum, and would, 

 therefore, be deposited on the wall of the bowl were it 

 not for other factors that in a measure prevent this. 

 The movement of the fat toward the center of the bowl 

 carries into the cream a considerable proportion of the 

 bacteria in the milk. The slime will always contain 

 many more bacteria than the milk, but the per cent of 

 bacteria thus removed is relatively low, due to the small 

 amount of slime obtained from the milk, so that the ac- 

 tual effect of clarification on the keeping quality of 

 milk is insignificant. The complete removal of all in- 

 soluble and therefore visible dirt is, however, regarded 

 of sufficient value to warrant the use. 



Machines designed especially for the clarification of 

 rnilk are now widely used. They differ from the cream 

 separator in that the milk is introduced at the outside 

 of the bowl and hence there is no separation of the fat 

 from the serum. It is claimed that the removal of the 

 dirt, cells from the interior of the udder and bacteria 

 is as efficiently done as when the separator is used. The 

 advantages claimed for the machine are that it has no 

 effect on the subsequent gravity creaming of the milk 

 and that less power is demanded thai? for the separator. 



From the standpoint of the consumer, all processes by 

 which dirt is removed from milk are objectionable, since 



