370 DEDUCTIONS FROM ANALYSIS. 



milk or cream used for the preparation of the cheese. Expressed 

 as formulse 



j r\f\ "ni 



Fat in original milk = . p 4. T? ~^~ ^'^* 



100 P 333 P 



Solids not fat in original milk = 10 . 62p + . 3F or 35 . 4p + g . 



1 0-354 P , 



F^Ki5= -IT 



Owing to the natural variations of the ratio of fat to proteins 

 in cheese, and of the loss of fat in the whey, no cheese should 

 be certified by this method to be made from skimmed milk 

 unless the calculated fat is less than 2-75 per cent. Similarly 

 it is not advisable to condemn a cream cheese unless the calculated 

 percentage of fat falls below 10 per cent. 



The addition of foreign fat is detected by an examination of 

 the fat by the methods given under Butter Fat. The fat ex- 

 tracted during the process of analysis may be used. The cheese 

 may be boiled with water to which a little alkali has been added, 

 or shaken with boiling water, and then with an equal bulk of 

 sulphuric acid 1-820 specific gravity (as recommended in the 

 Gerber process). If the cheese has been extracted with water 

 and ground up in a mortar, in most cases the bulk of the fat 

 separates in the form of butter, and the fat can be separated 

 readily from this. 



Devarda recommends triturating 50 to 100 grammes of cheese 

 with a little water in a mortar, mixing with 50 to 80 c.c. of water 

 and 100 to 150 c.c. of ether in a stoppered flask and shaking with 

 dilute potash till a red colour is shown with phenol-phthalein. 

 The ethereal layer is driven off, the ether distilled, the fat dried 

 at 100 C. and filtered (if necessary). 



W. N. Yarrow digests the cheese with hydrochloric acid till 

 the fat floats on the surface, and washes this with water till 

 neutral. 



It must be borne in mind that certain changes may take place 

 in the fat, and that the limits of composition of butter fat do 

 not apply quite so rigidly to cheese fat. As, however, any 

 addition of fat is usually large relatively to the butter fat left in 

 the cheese, there is not much difficulty in detecting its presence. 



