CASEIN : ITS ORIGIN, PREPARATION AND PROPERTIES. 5 



(0'6 per cent.), lactoglobulin (traces) and lactoprotein are also 

 present. Owing to the force of circumstances, it is seldom that 

 casein products are prepared in the same place as the crude 

 casein is produced, the raw material being generally obtained 

 from dairies at a distance. For this reason the description of 

 the mode of preparing the crude casein will be confined to the 

 indispensable minimum. 



Casein is recovered from skim milk (whole milk con- 

 taining too much valuable butter to be used for the purpose) 

 by throwing down the suspended substance with suitable 

 reagents. These may be of two kinds. On the one hand, 

 as already mentioned, acids, including the lactic acid formed 

 as a fermentation product of the milk sugar, will curdle the 

 milk and thus precipitate the casein ; and, on the other, the 

 same result can be brought about by the use of certain fer- 

 ments, of which the rennet ferment, lab, is the chief. At 

 one time it was thought the product was the same in both 

 cases, but careful experiment has shown that a considerable 

 difference exists between them, pure casein being obtained 

 when acids are used, whereas rennet furnishes the so-called 

 paracasein, a fission product of the ordinary substance. 

 Hence it is necessary to keep the two reagents distinct, 

 this being a point of special importance when cheese-mak- 

 ing is in question. 



In order to secure the correct precipitation of the casein 

 the milk must be kept at a certain temperature, not exceeding 

 140 F. or lower than 68 F., since beyond these limits the 

 action of the rennet is weakened and very imperfect. The 

 milk may be warmed either by direct fire heat or by steam, 

 a jacketed pan being used in the latter case. 



We will leave out of consideration the primitive pans, 

 suspended over a wood fire, and refer only to the form shown 

 in Fig. 1, which represents a pan surrounded by brickwork 

 (a) with an annular flue (6) between the pan and the brick- 



