No. 6. DJE!:PAKTMi<:iN'T OF AGK.CL .LTUKK. 5«1 



[L) Actiou of Heat on Casein. — Heat alone under oidinarj- coodi- 

 Lions, even at boiling point, doe&knot coagulate casein in milk. The 

 loimation of a peculiar skin on the surface of milk heated above 

 140 degrees F., is largely due to the casein of the milk, and not to 

 albumin, as was formerly supposed. The skin itself contains practi- 

 cally all the constituents of milk and is a kind of evaporated milk. 



(g.j Action of Kennet on Milk-Casein. — One of the most charac- 

 teristic properties of milk-casein is its coagulation by rennet, this 

 property making it possible to manufacture cheese from milk. The 

 curd formed by action of rennet is a compound different from casein 

 and is called paracasein. The coagulation of casein by rennet i* 

 quite different from that produced by acids. In connection with the 

 subject of cheese-making, we will consider in detail the properties 

 of rennet and the conditions that affect its power to coagulate with 

 milk-casein. 



1,3.) Milk-Albumiu. — Milk-albumin differs from milk-casein in many 

 ways, the most important of which we will briefly notice. First, 

 milk-albumi'ii is not acted on by rennet; second, it is not coagulated 

 by acids at ordinary temperatures; third, it is coagulated by heat 

 alone, though not completely, above IGO degrees F. From these 

 characteristic differences, it can readily be seen that casein and al- 

 bumin are very different compounds. 



(4.) Galactase in milk was discovered by Dis. liabcock and Russell 

 about five years ago. It is present in very small amounts. It has 

 the power of acting upon milk-casein, first changing it into a solid 

 and lihen dissolving it. It is believed to be active in cheese ripening. 



(5.) Amount of Casein and Albumin in Milk. — In general, the 

 amount of casein and albumin, taken together, are found in milk in 

 (juantiries ranging from 2.50 to 6 per cent.; the average is about 

 ■i.2 per cent. There is about 3.5 times as much casein as there is 

 albumin. 



(a.) Cafi'ein. — Casein in milk varies from 2 to 4 per cent., and 

 averages 2.50 per cent. 



(b.) Albumin. — Albumin in milk varies from 0.50 to 0.90 per cent., 

 and averages 0.70 per cent. 



(('.) Influence of Lactation on Casein and Albumin. — There is a 

 vitry general te^idency for casein and albumin to increase in milk 

 as the period of lactation advances, and somewhat more rapidly 

 in proportion than the milk-fat. 



5. Milk Sugar. 



-Milk-siigar is present in cows' milk in solution. In general com 

 position it resembles our ordinary sugar, but its sweetness is very 

 much less than that of cane sugar, and it is also less readily soluble 

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