20 
BULLETIN 1344, U. S. DEPAETMENT OF AGRICULTURE 
In Table 21 are shown the results of a similar test where the 
samples were held and agitated for 15 minutes. The results are 
similar to those in the previous tables, except that during the heating 
period the holding and agitating had very little effect. Samples 
that were held and agitated for 15 minutes at various temperatures 
between 90° and 60° F. after pasteurization showed a decrease in 
cream volume, as was also shown in Tables 19 and 20. 
Table 21. — Effect of alloicing milk to stand, and also of agitation for 15 minutes 
at various temperatures before and after pasteurization 
[All samples cooled to 45° F. before being placed in storage] 
Description 
Tempera- 
ture at 
which 
held and 
agitated 
Cream volume after 20 hours 
Sam- 
ple 
No. 
Control 
(cooled 
at once) 
Allowed 
to stand 
15 min- 
utes 
Held and 
agitated 
for 15 
minutes 
before 
cooling 
1 
°F. 
48 
70 
85 
92 
100 
110 
120 
130 
145 
145 
90 
70 
60 
17.5 
18.0 
17.0 
17.0 
17.0 
17.0 
17.0 
17.0 
17.0 
16.0 
14.0 
13.5 
13.0 
2 
Heated to 70° 
17. 5 
16. 5 
17.0 
16.5 
16. 5 
17.0 
17.0 
17.5 
3 
Heated to 85° 
15. 5 
4 
Heated to 92° . 
16. 5 
5 
Heated to 100° 
16.5 
6 
Heated to 110° 
16.5 
7 
Heated to 120°. . 
17.0 
8 
Heated to 130° 
17.0 
9 
Heated to 145° 
10 
Heated to 145° for 30 minutes 
11 
Cooled in can to 90° 
12.0 
12. 5 
12.5 
12.0 
12 
Cooled in can to 70° . 
12.0 
13 
Cooled in can to 60° 
12. 5 
The data in Tables 19, 20, and 21 indicate clearly that holding or 
agitating milk for any length of time at temperatures between 120° 
and 60° after pasteurization has a detrimental effect on the cream 
volume. The effect of such holding and agitating on samples taken 
at different temperatures while the milk was being raised to the pas- 
teurization temperature was much less marked. The data plainly 
indicate that it is not advisable to cool milk in the vat below 120° 
to 110° F; it should be cooled from that temperature to below 50° 
over a separate cooler. The data also indicate, though less emphati- 
cally, that the milk should be heated during pasteurization from 60° 
to 110° F. as quickly as possible and with a minimum of agitation. 
Agitation of the milk at 145° had very little effect on the cream vol- 
ume. It will be noted that at temperatures between 110° and 60° F. 
the milk that was agitated had a poorer cream volume than that 
which was not agitated; also that in all cases the milk that was held 
without agitation at temperatures below 120° showed a poorer cream 
volume than that which was immediately cooled. 
The results of these tests have a practical bearing on the commer- 
cial handling of market milk. They show clearly the advantages 
of cooling milk quickly after pasteurization, with as little agitation 
as possible between the temperatures of 120° and 60° F. They indi- 
cate that it is detrimental to pump the milk at these temperatures 
and also to cool in the vat below about 120° F. after pasteurization. 
Best results are obtained by cooling from 120° to below 50° over a 
separate cooler. 
