90 GUIDE TO DAIRYING IN SOUTH AFRICA 



Showing the difference between butter and animal 

 fat. 



Casein. 



This is present in milk in suspension and partly 

 in solution, the average amount being three per cent. 

 The amount present is practically always the same, 

 but it may vary slightly from 2*5 to 3*5 %, and 

 it is the object of cheese-making to recover the 

 casein from the milk, which is brought about by the 

 activity of rennet with formation of lactic acid and 

 change of casein into an insoluble form. It is then 

 known as the curd, and contains the milk fat em- 

 bedded in the mass. 



Albumin. 



The amount present in milk is from 0*5 to 

 75 % It is present in solution, but when the 

 milk is boiled it coagulates and forms a skin on the 

 top of the milk. It is not coagulated by rennet, 

 and it closely resembles the white of eggs. When 

 milk is boiled it acquires a different taste to fresh 

 milk ; this is on account of the albumin being set 

 free. The amount present in milk does not vary 

 except in cases of newly calved cows, when the 



