178 BUTTER-MAKING. 
over the heating-surface only by force of its own gravity, a 
heavy layer of curd usually adheres. This is due to the fact 
that certain portions of the milk are exposed to the excessive 
heating too long, while if caused to move rapidly it does not 
remain in contact with one portion of the heating-surface long 
enough to cause it to adhere to so great an extent. 
Fic. 118.—The Simplex regenerative pasteurizer (assembled). 
The condition of the milk or cream has some influence upon 
the degree of adhesiveness of curd on the heating-surface. 
Sour and coagulated milk adheres or burns on to a greater 
extent than does milk or cream in good condition. This is 
evidently due to the lesser fluidity of the sour milk, and, as a 
consequence, it does not move over the heating-surface so: 
rapidly, and therefore burns on. Milk which contains a great 
deal of air or scum also adheres to the heating-surface much 
