884 MILK. 



Carbon 40.0 



Hydrogen 6.7 



Oxygen 53.3 



100.0 



Buttct To understand the preparation of butter thoroughly, it 

 is absolutely necessary to know the physical constitution of the 

 milk from which it is obtained. Now the microscope shows us that 

 milk holds in suspension an infinity of globules of different dimen- 

 sions, which, by reason of their less specific gravity, tend to rise to 

 the surface of the liquid in which they float, where they collect, 

 and by and by form a film or layer of a diflferent character from the 

 fluid beneath ; the superficial layer is the creairu, and this removed, 

 the subjacent liquid constitutes the skim-milk. This separation ap- 

 pears to take place most completely in a cool temperature from 54" 

 to 60" F. 



Allowed to stand for a time, which varies with the temperature, 

 milk becomes sour, and by and by separates into three strata or 

 parts : cream, whey, and curd, or coagulated caseum. By suffering 

 the milk to become acid before removing the cream, it has been 

 thought that a larger quantity of this, the most valuable constituent 

 of the milk, was obtained ; and the fact is probably so ; but in dis- 

 tricts where the subject of the dairy has been most carefully stud- 

 ied, it has been found that it is better to cream before the appearance 

 of any signs of acidity have appeared. WTien a knife can be push- 

 ed through the cream, and withdrawn without any milk appearing, 

 the cream ought to be removed.* 



Butter is obtained from cream by churning, as all the world 

 knows ; by the agitation, the fatty particles cohere and separate from 

 the watery portion, at first in smaller and then in larger masses. 

 The remaining fluid is buttermilk, a fluid slightly acid, and of a very 

 agreeable flavor, containing the larger portion of the caseous element 

 of the cream coagulated, and also a certain portion of the fatty 

 principle which has not been separated. 



The globules of milk appear, from the latest microscopical ob- 

 servations,f to be formed essentially of fatty matter, surrounded with 

 a delicate, elastic, transparent pellicle. In the course of the agita- 

 tion or trituration of churning, these delicate pellicles give way, and 

 then the globules of oil or fatty matter are left free to cohere, which 

 they were prevented from doing previously, by the interposition of 

 the delicate film or covering of the several globules. Were the 

 butter simply suspended in the state of emulsion in the milk, we 

 should certainly expect that it would separate on the application of 

 heat ; but this it does not : cream or milk may be brought to the 

 boiling point, and even boiled for some time, without a particle of 

 oil appearing. Could M. Romanet show any of these pellicles, 

 apart from the oil-globules they enclose, it would be very satisfacto- 

 ry, and would certainly enable' us to explain the effect of churning 



Churning is a longer or shorter process, according to a variety of 



* Thaer, Princlpes, tc, t. iv. p. 34L 

 , t M. Bomanet, MSS. 



I 



