CHURNING. 333 



gravity is usually between 1-034 and 1-037. Its average com- 

 position as given by Fleischmann is 



Setting. Separator. 



Water ... 89-85 90-30 



Fat ... ... 0-75 0-25* 



Proteids ... 4-03 -1-00 



Milk sugar ... 4-60 4-70 



Ash 0-77 0-75 



100-00 100-00 



X 



Butter is produced by agitating or "churning" milk, or more 

 generally cream, until the fat globules coalesce. The resulting 

 semi-solid mass which separates from the butter-milk consists 

 largely of completely continuous fat, a few of the original 

 globules, however, remaining. Under the microscope many 

 spherical globules are visible, which, according to recent obser- 

 vations, consist of minute drops of enclosed butter-milk or 

 water and not of fat. 



The effect of churning is purely mechanical; the fat globules 

 are by violent motion knocked together and adhere, thus giving 

 rise to larger, irregular masses, which in turn collide together 

 or with other fat globules. In this way the masses of fat 

 gradually increase in size, portions of the aqueous liquid be- 

 coming enclosed during their formation. At first the increase 

 in size of the fat particles and their irregular shape give rise to 

 increased viscosity (this phenomenon is sometimes known as 

 " going to sleep") ; but as they grow larger they tend to sepa- 

 rate more completely from the butter-milk and float, the con- 

 tents of the churn becoming mobile. The butter grains are 

 then, by working, pressed together, and more and more of the 

 butter-milk is separated from the fat. In order that the 

 amount of liquid retained by the butter may be small, it is 

 necessary that the temperature should be carefully adjusted. 

 The optimum temperature, however, depends partly upon the 

 temperature at which the cream has been for some time prior 



* In the author's experience, separated milk generally contains much less fat than 

 this. With ;i>oo<l management probably not more than O'l % of fat should be left in the 

 separated milk. 



