60 CHEESE MAKING. 
Do not allow the curd to collect in the corners of the vat, 
and be sure and rub it off from the sides of the vat or it will 
scald on. The whey should look clear, and be as free as possible 
from specks of curd floating in it. 
128. Heating the Curd. 
Curd being a poor conductor of heat, a rise of one degree 
jn five minutes is fast enough to heat normal working milk. If 
it is heated too fast, it will cook the particles on the outside and 
retain the whey inside of the curd; the result will be a mottled 
whey-soaked cheese. (184.) 
129. Cooking an Over-Ripe Curd. 
If the milk is over-ripe, however, it expels the whey faster, 
and the curd must be heated faster and higher than in the case 
of a normal working curd, or there will be the required amount 
of acid on the curd before it is hard enough to remove it from 
the whey. As a usual thing it is not necessary to cook a curd 
above ninety-eight degrees, but a curd must be cooked before 
drawing the whey, no matter if the temperature has to be raised 
to one hundred and ten degres to do it. (For definition of 
cooked curd, see paragraph 133.) It is necessary to cook a fast 
working curd in that way, and if the curd is taking acid too 
rapidly for the heating in the whey to be sufficient to firm the 
curd before the acid is too great, the whey can be drawn and the 
remainder of the firming done in warm water, which is run into 
the vat in place of the whey. (See, however, paragraph 143 re- 
garding this.) 
130. Stirring the Curd. 
To assist the curd in heating evenly and keep it from mat- 
ting together, it should be stirred from the time it is cut till it 
is cooked. Some Canadian factories have a steam stirring ap- 
paratus which is very handy, but in most factories stirring is 
done with a rake. 
131. Curd Rakes. 
There are two kinds of curd rakes in use, the common 
wooden hay rake and the McPherson curd rake. 
The rake is put into the whey as soon as the steam is turned 
on, and the curd is started into a rolling motion as though it 
