16 BUTTER-MAKING. 



of time after milking, the caseous matter (or the nitrogenous 

 matter combined with hme) tends to separate. The caseous 

 matter of milk is not completely precipitated by heat, although 

 heat partially destroys the union between the casein and lime. 

 This destroys the action of rennet. Instead of getting a smooth 

 sohd coagulum, a more flaky precipitate is obtained. For this 

 reason milk for cheese-making should not be heated to a high 

 temperature. By heating milk in a glass flask to a high tem- 

 perature, and letting it stand for a time, it will be found that 

 a mineral precipitate has settled to the bottom. This pre- 

 cipitate is believed to be a hme phosjDhate, which, previous 

 to heating, was combined with the casein of the milk. By 

 adding calcium chloride (C;X'l2) to milk which has been heated, 

 its normal condition towards the action of rennet is again 

 restored. 



Albumen. — If the casein is removed from the milk by 

 precipitation, and then filtered off, the filtrate will contain a 

 substance \\'hich will precipitate when boiled. This is albumen, 

 and is similar in character to albumen from the white of an 

 egg. It differs from casein in that it is not precipitated by 

 rennet or acids, but precipitates on heating. It does not 

 contain any phosphates, but contains a comparatively large 

 amount of sulphur. 



As the albumen is soluble in rennet and dilute acids, it 

 can readily be seen that it is retained in the whey obtained in 

 cheese-making. AVhen albumen is present in small quanti- 

 ties, as it is in normal milk, heating does not completely pre- 

 cipitate it, unless the casein or curd is first removed. If, on 

 the other hand, albumen is present in excess, as is the case 

 in colostrum, the major portion of the albumen is precipitated 

 when heat is applied, without first removing the casein. 



Sugar.- Milk-sugar occurs in milk to the extent of about 

 5%. It varies very little in quantity, seldom falling below 

 3^% and seldom rising above 5^%. It occurs in solution, 

 and is found in no other place in nature. 



Milk-sugar is the most unstable component of milk. It 



