CASEIN: ITS OKIGIN, PREPAKATION AND PROPERTIES. 9 



boiler is being cleaned. The pipe (g) is employed as an over- 

 flow in filling the boiler, to prevent over-filling and indicate 

 when enough water has been run in. 



When the milk to be curdled has been raised to the 

 proper temperature in one of the utensils just described, it is 

 treated with the rennet. At first no change is apparent, but 

 after some little time the milk begins to curdle, having 

 thickened just before, and the precipitation of the casein 

 is soon complete. At a temperature of 95 F., one part of 

 good rennet is sufficient to curdle 10,000 parts of milk within 

 forty minutes, whilst two parts will effect the same result in 

 half the time, or curdle double the quantity in the same 

 tinle. For a given temperature and a definite quantity of 

 milk, the time required for coagulation varies inversely with 

 the amount of rennet used. 



Rennet which has been used once loses its power almost 

 entirely, it being difficult to curdle a fresh batch of milk 

 with the whey from the previous one. From this it follows 

 that the curdling of milk by rennet must be regarded as 

 a very protracted chemical process, which does not become 

 apparent until it has proceeded to a certain stage. The 

 stronger the action of the rennet, and the sooner the casein 

 is thrown down, the more powerful the contraction of the 

 curd and the larger the volume of whey expressed. This 

 means a reduction in the residual water in the curd and an 

 increase in its final dryness and firmness. Hence the man- 

 ner in which the rennet acts is of considerable importance 

 to the character of the casein. 



This latter is also influenced by the quantity of rennet 

 used, the temperature at which it is allowed to act, and 

 finally by the character of the milk, or rather the casein 

 therein. The character of the casein reacts on the influence 

 of the rennet, and the same applies to the reaction of the 

 milk, an acid reaction favouring the working of the rennet, 



