144 BUTTER-MAKING. 



sionally it happens that a machine is run backwards. This is 

 likely to cause the cover of the bowl to run off. 



Thickness of Cream. The efficiency of skimming depends 

 to some extent upon the thickness of the cream skimmed. 

 Most separators, however, will skim within quite a wide range 

 as to thickness. The richness of cream usually skimmed by 

 separators is about from 25% to 50%. Most separators, how- 

 ever, will do good skimming even if the cream contains as high 

 as 60% fat. This, however, should be considered to be about the 

 maximum, in order to get the best results from a separator. 



Slush in Bowl. As has been mentioned before, there is 

 always a thick, slimy substance which adheres to the bowl- 

 wall. The composition of separator-slime is, according to 

 Fleischmann, as follows: 



Water 67.3 



Fat.. 1.1 



Caseous matter 25.9 



Other organic substances 2.1 



Ash. . 3.6 



100.0 



At the center of the bowl, or along the axis which runs 

 perpendicular in the bowl, there is always considerable cream. 

 It is practically impossible to get all the cream out of the bowl, 

 even if it is flushed with much water. The amount of slush 

 varies somewhat with the different kinds of separators. For 

 this reason, it is essential that it should be taken into con- 

 sideration when the comparative efficiency of skimming of 

 different separators is considered. When the test extends over 

 a comparatively long period, arid the milk skimmed amounts 

 to several thousand pounds, then the bowl -slush does not affect 

 the conditions for comparative results very much; but when 

 the test is short, and only a hundred pounds of milk, or a similar 

 amount, is skimmed, then the amount of fat left in the bowl- 

 slush will have considerable influence upon deciding which one 

 is the most efficient machine. 



