MANUFACTURE OF CHEESE. 



387 



•wticli tben readily collects in a mass, aud, wlien duly separated from the otheT 

 substances, is butter. 



Wben milk is suffered to remain at rest tbe oily particles slowly separate, 

 and being; lighter than the liquid holding them they rise to the surface, aud, to- 

 gether with a portion of the cheesy matter, form the unctuous clot or coat on 

 the surface called cream. The fatty matter does not wholly separate, as a por- 

 tion remains in suspension, and in proportion to the completeness of the separa- 

 tion the liquid assumes more or less of a bluish tint. Being only i?uspeuded, 

 the separation of butter from milk is to a considerable extent a mechanical pro- 

 cess. Casein, on the contrary, is dissolved in the water of the milk, and not 

 merely suspended in it. Its separation is a chemical process. By what 

 means it is thus held in solution is not known. Casein, under ordinary circum- 

 stances, is insoluble in pure water. It will dissolve in water in which a little 

 soda is added. Freshly drawn milk sometimes contains a little free soda, and 

 when this is the case it is slightly alkaline, aud nearly all writers on the chem- 

 istry of milk teach that it is by virtue of the presence of this free alkali that the 

 cream is held in solution. Thus Dr. Lyon Playfair, says : 



" Milk contains about four and a half per cent, of casein. It is held in solution in the milk 

 by means of an alkali. Any acid which removes this alkali converts the cream into an inso- 

 luble curd, which, when collected and dried, forms cheese. The acid formed when milk 

 becomes sour also produces the same efl'ect. Prepared reuuet is a means of etfecting this 

 change." 



Professor Johnston says : 



"As it comes from the cow, milk contains a quantity of soda not combined with any acid, 

 by which soda the curd is believed to be held in solution. As the milk becomes sour the 

 soda combiufs with the lactic acid, and thus the curd becoming insoluble separates from the 

 whey, or the milk thickens and curdles. Kennet, when added to the milk, changes the sugar 

 into the acid of milk. The addition of rennet, therefore, is only a more rapid way of makino* 

 milk sour." 



Professor S. W. Johnson, of Yale College, has favored me with the following recent and minute analysis of 

 milk by eminent chemista iu Kurope: 



Cotfs' milk examined by Boclder and Struckmann, 



Ingredients in 1,000 parts. 



Water 



Total solid matters 



Caueln 



Albumen 



Butter 



Milk sugar 



bulls 



M«miug's milk. 



899.7 



100.3 



:;:;. 4 



4.4 



21.7 



43.0 



8.3 



Xoon milk. 



892. 



lOsi. 



23. G 



3.2 



2ti.3 



47.2 



6.9 



Evening's milk. 



866.0 

 134.0 

 27. 2 

 *'3!l 

 54.2 

 41.0 

 7.8 



The butter in evening's milk is here stated to be double that in morning's milk. Professor Johnson remarks 

 that this has been conuborated by other observers in both cows' and goats' milk. I am not aware that this 

 has proved to be the case usually iu this country. My own observations have showu only a trifling diflference. 



Milk from coics of various breeds. 



