SEPARATION OF CREAM FROM THE MILK. 547 



few days turns it sour. If, however, the milk be boiled every morning 

 or every second morning, the souring property of the casein is at every 

 boiling destroyed again, and the milk may thus be kept fresh for two 

 months or more. 



4°. Another mode of preserving milk is to evaporate it to dryness by 

 a gentle heat, and under constant stirring. By this means a dry mass is 

 obtained which may be preserved for a length of time, and which when 

 dissolved in water is said to possess all the properties of the most excel- 

 lent milk. It is known in Italy by the name of latteina. [II latte e i 

 suoi prodotti, p. 19.] 



§ 8. Of the separation and measureinent of cream, the galaciometer, the 

 composition of cream, and the preparation of cream-cheese. 



1°. Separation of cream. — The fatty part of the milk which exists in 

 the cream, and which forms the butter, is merely mixed with and held in 

 suspension by the water of which the milk chiefly consists. In the 

 udder of the cow it is in some measure separated from, and floats on, the 

 surface of the milk, the later drawn portions being always the richest in 

 cream. During the milking, the rich and poor portions are usually 

 mixed intimately tojgether again, and thus the after-separation is render- 

 ed slower, more difficult, and less com|)lete. That this is really so, is 

 proved by two facts — first, that if milk be well shaken or stirred, so 

 as to mix its parts intimately together before it is set aside, the cream 

 will be considerably longer in rising to the surface — and second, that 

 more cream is obtained by keeping the milk in separate portions as it is 

 drawn, and setting these aside to throw up their cream in separate ves- 

 sels, than when the whole milking is mixed together. When the collec- 

 tion of cream, therefore, is the principal object, economy suggests that 

 the first, second, third, and last drawn portions of the milk should be 

 kept apart from each other. Even in large dairies this could easily be 

 effected by having three or four pails, in one of which the first, in 

 another the second milk, and so on, might be collected. 



Cream does not readily rise through any considerable depth of milk ; 

 it is usual, therefore, to set it aside in broad shallow vessels in which the 

 milk stands at a deptli of not more than two or three inches. By this 

 means the cream can be more effectually separated witliin a given time. 



But the temperature of the surrounding air materially affects the 

 quantity of cream which milk will yield, or the rapidity with which it 

 rises to the surface and can be separated. Thus it is said that from the 

 same milk an equal quantity of cream may be extracted in a much 

 shorter time during warm than during cold weather — that, for example, 

 milk may be perfectly creamed in — 



36 hours, v/hen the temperature of the air is 

 24 u .i u 



18 to 20 hours " '' " 



10 to 12 



— while, at a temperature of 34° to 37*^ F., milk may be kept for three 

 weeks, without throwing up any notable quantity of cream (Sprengel). 



The reason of this is that the fatty matter of the milk becomes partially 

 solidified in cold weather, and is thus unable to rise to the surface of ihd 

 milk so readily as it does when in a warm and perrisctly fluid state- 



