MANUFACTURE OF CASEIN. 23 



burlap press cloths and put to press. While burlap is generally used 

 for pressing the skim-milk curd it is not so satisfactory as duck, 

 since the curd adheres to it more and makes washing more difficult. 

 Continuous heavy pressure is applied until sufficient whey has been 

 expelled to permit satisfactory grinding. The time required depends 

 upon the degree of pressure and the condition of the curd. The 

 usual practice is to allow the curd to remain in the press over night. 

 After it has been pressed properly the curd is taken from the press 

 and, after being run through the curd mill, the ground curd is 

 placed upon the trays and dried in the tunnel drier. 



PRESSED-CURD METHOD. 



Creameries without a sufficient quantity of skim milk to justify 

 the expense of installing a complete plant for manufacturing the 

 dried casein may ship the pressed curd to a central drying plant, 

 several of which are maintained by casein jobbers in creamery dis- 

 tricts. At the central drying plant the green-pressecl curd is ground, 

 dried, and paid for on the basis of dried casein obtained. When 

 the pressed curd is shipped the only equipment required besides the 

 vat is the press, press cloths, and dividing boards, none of which are 

 expensive. 



The green curd has to be shipped frequently during the warm 

 weather, unless it can be kept in a refrigerator, and must remain 

 in transit only a very short time. The green-pressed curd soon be- 

 gins to mold, which has an injurious effect upon the quality of 

 the casein. 



COOKED-CURD METHOD. 



The cooked-curd method of making skim-milk casein is coming 

 into more general use among the creameries in districts convenient 

 to a central drying plant. This method requires practically no 

 equipment except the precipitating vat. The process of precipitat- 

 ing is the same as that used for pressed curd ; that is, the skim milk 

 is heated to 120° F. (48.89° C.) and sulphuric acid added at the rate 

 required to separate properly. After draining the whey off the curd 

 is broken up in the vat, covered with water, and the mixture heated 

 to a temperature of 170° to 175° F. (76.67° to 79.44° C.) by means of 

 direct steam. At that temperature all the curd should collect in a 

 semifluid, plastic, tough mass. The water is drained off and the 

 soft curd placed in a barrel, where it settles into an almost air-tight 

 mass which upon cooling changes to a very tough, impervious mass 

 that will keep for several days, even in hot weather. Fresh-cooked 

 curd can be put on top of the hardened curd in a barrel partially 

 filled from a previous batch. The barrels filled with cooked curd 

 and covered with burlap can be shipped to the central drying 

 plant without danger of breaking. Cooked curd is very hard to 

 grind and requires an especially strong mill. 



