22 
BULLETIN 240, U. S. DEPARTMENT OF AGRICULTURE. 
temperature dropped from 145° to about 100° F. The milk wastheo 
allowed to stand at a temperature of from 100° to 80° F. for five 
hours, after which it was placed in a refrigerator at 45° F., where it 
cooled slowly in still air. The remaining bottle was cooled for half 
an hour in an air blast at room temperature and allowed to remain 
at a temperature of about 75° F. through the entire experiment. The 
results of these experiments are given in Table 7. 
Table 7. — Effect of different methods of cooling on the bacterial content of 
pasteurized milk. 
Method of cooling. 
Sample No. . 
1 
2 
3 
Bacteria per e.c. 
9,050,000 
6,450 
5,050 
4,800 
1,370,000 
7,150 
6,100 
6,200 
9,600 
2,760,000 
4,950 
6,850 
700,000 
2,750,000 
460,800,000 
Bacteria per e.c. 
Bacteria per ex. 
11,900,000 
8,500 
28,400 
76,500 
Bottle No. 1, cooled quickly:, 
2,110 
• 1,720 
2,340 
885,000 
2,580 
1,600 
2,400 
, 2,740 
850,000 
2,180 
2,890 
2,420,000 
13,400,000 
Held at 45° F. for 22 hours 
Held at 75° F. for 24 hours 
Bottle No. 2, cooled slowly: 
11,900 
29,000 
192,000 
Held at 45° F. fcr 17 hours 
348,000 
Held at 75° F for 24 hours. 
Bottle No. 3, cooled at room temperature: 
8,500 
25,000 
Held at 75° F. for 22 hours 
83,400,000 
Held at 75° F. for 28 hours, 
269.000.000 
Held at 75° F. for total of 66 hours 
1 
A study of the table shows that there was no increased bacterial 
growth with samples 1 and 2 caused by holding the pasteurized milk 
for five hours after bottling hot, even though the temperature dur- 
ing that period ranged from 100° to 80° F., which is the most favor- 
able temperature for bacterial development. With sample 3 there 
was an increased growth over that in the milk cooled quickly. It 
must be remembered that these experiments represent extreme con- 
ditions in slow cooling, but the fact is apparent that the cooling 
process should not extend over five hours. The effect of not cooling 
milk to low temperatures is plainly shown in the table by a compari- 
son of the bacterial counts with those of milk cooled both quickly 
and slowly. It is believed from these experiments that it is possible 
to cool hot bottled pasteurized milk by a blast at room temperature 
followed by a blast of cold air without any more bacterial develop- 
ment than would take place if the milk were immediately cooled, 
provided the milk is cooled to 50° F. gradually within five hours. 
This is not made as a definite statement, because different results 
may, of course, be obtained when milk is thus cooled on a commercial 
scale. 
Again let the fact be emphasized that pasteurized milk or raw milk 
must be kept at low temperatures after cooling in order to check bac- 
terial development. 
