222 DAIRY TECHNOLOGY 



acidity of the solution one tenth per cent. This causes 

 the precipitation of the casein. It is then filtered and 

 washed well with distilled water. This latter will dissolve 

 out the acid and sugar in the residue. This residue on 

 the filter is dried and redissolved in the least possible 

 amount of ammonia, and upon standing awhile, the fat 

 will rise to the top. The liquid can then be siphoned off 

 and filtered. The filtrate is again precipitated by acetic 

 acid. This precipitate is redissolved in ammonia and the 

 process is repeated three or four times until it is pure and 

 white. This casein is now rubbed in a mortar with 80 per 

 cent alcohol and the alcohol poured off. This treatment 

 with alcohol is repeated several times, absolute alcohol 

 being used the last time. This is followed by treatment 

 with ether until all the alcohol is removed. The product is 

 pure casein which, when thoroughly dried, is in a powdery 

 condition. However, the preparation of casein for com- 

 mercial purposes is quite a different process. 



Commercial casein is prepared from skim milk on quite 

 a large scale, usually in a room or building adjoining a 

 large whole-milk creamery. 



Five thousand or more pounds of skim milk are placed 

 in a jacketed vat and heated to about 130 F. Then 

 sufficient acid is added to precipitate the casein. In some 

 cases commercial sulphuric acid is used in the proportion 

 of one pint of acid diluted in water to one thousand pounds 

 of milk. At other factories the kind and quantity of acid 

 used are considered trade secrets. The curdling should 

 take place under proper conditions. If an excess of sul- 

 phuric acid or too strong acid is used, the curd will be 

 discolored. 



When the milk has been coagulated, the whey separates 

 and is drawn off. To facilitate and hasten this process, 



