384 OTHER MILK PRODUCTS. 



tte fat by the metliods 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 bidk of 

 sulphuric acid r820 specific gravity (as recomrnended in the 

 G-erber 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 readily separ- 

 ated 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 phenolphthalein. 

 The ethereal layer is drawn ofi, 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 difiiculty in detecting its presence. 



Chemical Control of Cheese-making. — The amount of cheese 

 in pounds that may be expected to be obtained from 10 gallons of 

 milk may be calculated by one of the following formulae : — 



(i.) lb. of cheese = {Solids not fat x 0-3 + (fat — 0-23)} x — . 



■' 55 



(ii.) lb. of cheese = {aldehyde figure X 0-135 + (fat — 0-23)} 



100 

 55' 



(iii.) lb. of cheese = {curd by Lindet's method x (fat — 0-23)} x — . 



These formulas give the weight of green cheese assumed to 

 contain 45 per cent, of water and salt, and apply fairly well to 

 such cheeses as Cheddar, Cheshire, and Stilton. 



The percentage of fat should be estimated in the whey, and 

 this should not exceed 0'3 ; a higher figure shows that the' curd 

 has been cut too soon, or carelessly. 



The acidity of the milk, the whey, and the curd should be 

 determined ; the milk before renneting should have an acidity 

 of 22° to 24°, the whey should be drawn at about the same acidity, 

 and the curd vatted when the acidity has reached about 100°'. 

 The acidity of the curd is best tested with a hot iron ; a small 

 piece of curd is placed on a hot iron, and immediately with- 



