140 BUTTER-MAKING. 
effect the different degrees of agitation of milk has upon the 
efficiency of separation: 
Av. Fat 
No. of Per Cent 
Experi- in 
ments. Skim- 
milk. 
Milk heated in vat, not pumped.................00 000s ee eee 10 =.117 
Milk heated in Pasteurizer, 200 revolutions of Bentaton perminute 8  .115 
“ce “e “ce be 250 es ce be 3 118 
ce 6c ““ “e 300 ce be be ce ec 8 134 
“ce oe be “ce 350 “6 be “ce ce “cé 2 143 
ce ce ce ee 400 ce ce ag “e “ci 7 .198 
tf ce oc“ ce 500 oe ce se ce ce 4 225 
Milk pumped by the parting pump at 122° Bc ssvedecaners 3 .129 
ee pee EG GAS Mia. cas alte ea beeen 3 119 
ios «« with the pump, cHECIIRE BU 2D eis secs eatin Dies 3 .117 
se ne ee ES ES Sn OA reac 8 ela taunt 3 .115 
In the above experiments the diameter of the agitator in 
the Pasteurizer was 14 inches. The speed at the periphery, 
at 250 revolutions per minute, was 5 feet per second. 
It will be seen from the above table that the higher the 
speed of the agitator, the greater the difficulty in getting a 
complete separation. Besides the speed of the agitator in 
the heating apparatus, undoubtedly the shape of the Pas- 
teurizer is a factor in determining the efficiency of the 
subsequent separation. For instance, the milk in most hori- 
zontal Pasteurizers is, even at low speed, exposed to con- 
siderable agitation. 
If the milk is suddenly heated from a low temperature to 
about 80° or 90° F. and then skimmed, the heating does not 
facilitate the skimming process very much. It is essential 
that the milk should be exposed to this temperature for a 
considerable time. The fat-globules do not warm as rapidly 
as the milk-serum. This diminishes the difference between the 
specific gravity of the two substances, consequently complete- 
ness of separation becomes more difficult. If milk is heated 
to a high temperature, say, for instance, 170° F., then the 
separation will be sufficiently complete without exposing the 
milk for any length of time to that temperature. 
