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-pressed 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 o.f 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 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. 
