THE CREAMING ABILITY OF MARKET MILK 17 
I to 46°. Agitation at that temperature (60° F.) apparently injured 
the cream volume. 
Sample No. 6 was cooled from 80° to 60° F., and after pumping 
the pumped samples were all cooled to 4G° and placed in storage. 
The No. 7 samples were pumped at 80° F. through the various 
pumps, and the samples with the control were placed in storage 
without cooling. Pumping affected this milk only slightly. 
The control on sample No. 8 was cooled from 80° to 46° F. before 
placing in storage. The milk was pumped at 80°, and all samples 
were cooled to 46°. The cream volume on the control sample in this 
case was apparently injured by the agitation in handling and in 
cooling. It will be noted that the No. 8 sample, after being pumped, 
had practically the same cream volume as samples 5, 6, ancl 7 after 
being pumped. 
Pumping pasteurized milk at 145° F. (samples 9 and 10) had 
little effect on the cream volume with any of the pumps used. 
Sample No. 11 was milk cooled in the vat after pasteurization to 
110° F. Two of the pumped samples were only slightly lower in 
cream volume than the control, although all samples, including the 
control, had a greatly decreased cream volume compared with the 
original milk. 
Sample No. 12 was old milk pasteurized and immediately cooled 
to 108° F. before pumping. Pumping at this temperature had a 
slight effect on the cream volume. 
Sample No. 13 was the same as No. 12, except that it was cooled 
to 54° F. The samples after being pumped at 54° were cooled to 
46° before placing in storage. Pumping the milk at this tempera- 
ture also had only a slight effect on the cream volume. 
Sample No. 14 after pasteurization was cooled slowly. The 
pumped samples showed a cream volume slightly less than the con- 
trol samples, although the cream volume of all these samples was 
decreased considerably as a result of the slow cooling. 
The results of the tests on pumping milk with the four pumps 
indicate the following: 
1. Pumping raw milk at temperatures between 36° and 50° F. and 
pasteurized milk at 145° had practically no effect on the cream vol- 
ume. These are the temperatures at which milk is most commonly 
pumped at commercial plants. 
2. Pumping and agitation at certain temperatures, especially be- 
tween 110° and 60° F., caused a reduction in the cream volume. 
EFFECT OF PUMPING RAW MILK AT COMMERCIAL PLANTS 
Further tests were conducted at milk plants to determine the 
effect of pumping raw milk under commercial conditions. The 
results at plants where the raw milk was pumped are shown in 
Table 17. The control samples upon which the differences in cream 
volume are computed were raw T milk collected from the receiving vat 
immediately after being emptied from the producers' cans and just- 
prior to pumping. A summary of the results obtained in the inves- 
i tigations shows that in seven instances there was no change in the 
f cream volume, while in most of the other cases the percentage of 
decrease was small. The average loss in cream volume on the 13 tests 
