THE DAIRY 207 



Milk powder is made by evaporating milk in thin layers in 

 a current of warm air and scraping off the film. So far as 

 the writer can ascertain, the yellowish- white powder which is 

 sold as dry milk contains less fat in proportion to the other 

 constituents than would be present in the residue from whole 

 milk. 



Cheese is produced from milk by the coagulation of the 

 casein, which carries down with it almost all the fat, leaving 

 the albumin and sugar in the whey. This curd is separated 

 from the whey as fully as possible, pressed and allowed to 

 ** ripen." 



The coagulation of the casein is usually effected by the 

 action of rennet, but it may be produced by acids — e.g.j by 

 the lactic acid resulting from the action of the lactic organisms 

 on the milk sugar. This is sometimes done in the pre- 

 paration of cream cheese. The curd and whey produced from' 

 whole milk by rennet have approximately the following 

 composition : 



Curd. Whey, 



Water ...... 50*0 92-04 



Fat 267 0-35 



Sugar 2-3 6-10 



Casein 20'0 0-46 



Albumin Trace 0-46 



Ash 1-0 0-69 



100-00 100-00 



Rennet acts most rapidly at a temperature of about 39° or 

 40° C. (102° to 104° F.), and then gives a firm and hard curd, 

 while in cooler or hotter milk — up to 50° C. ( = 122° F.) — the 

 curd formed is soft. 



So/t cheeses are made by coagulating the milk at 25° to 80° 0. 

 (77° to 86° F.), and always contain much moisture. 



ffard cheeses result when the curd forms in milk at about 



o 



