COOLING HOT-BOTTLED PASTEURIZED MILK. 
29 
in the milk cooled quickly. It must be remembered that these 
experiments represent extreme conditions 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 comparison of the bacterial counts 
with those of milk cooled both quickly and slowly. 
The results which have been thus far presented on the bacterio- 
logical effect of slow cooling were obtained from observations of bottles 
held under extreme laboratory conditions. We realize that labora- 
tory experiments do not always apply to commercial conditions, so 
the results shown in Table IV were determined from experiments 
conducted on a 30-crate basis. Two quart bottles of milk were 
examined in each experiment. The crates were stacked five high, 
and one bottle was placed in the lower crate and the other in the 
upper one. The cooling was conducted in the usual way, 30 crates 
being stacked in the cooling box, as has been described. This table 
shows the bacterial content of the raw milk, the bacterial content 
of the hot pasteurized milk bottle immediately after pasteurization 
for 30 minutes at 145° F. (62.8° C), and also the bacterial content 
after the bottles had been cooled by forced-air draft. 
Table IV. — Effect of slow cooling on bacterial content of pasteurized milk (milk cooled 
on a small commercial scale). 
Bottle 
No. 
Bacteria per cubic centimeter. 
Experiment No. 
Raw milk. 
After pas- 
teurization 
for 30 
minutes at 
145° F. 
After cool- 
ing by 
forced-air 
circulation. 
Length 
of cooling 
period. 
1 
i I 
{ I 
{ I 
{ I 
} 490,000 
| 128,000 
} 12,800,000 
} 140,800,000 
} 7,400,000 
/ 5, 400 
\ 7, 100 
/ 5, 000 
\ 4, 400 
/ 155, 000 
\ 156, 000 
J 525, 000 
\ 555, 000 
/ 132, 000 
\ 161, 000 
3,850 
2,850 
3,900 
4,400 
18, 900 
13, 900 
32, 000 
50,500 
95, 500 
78,500 
Minutes. l 
| 155 
} 150 
} 148 
} 127 
} 93 
2 
3 
4 
5 
1 Milk cooled to about 75° F.; in all the other experiments the milk was cooled to below 50° F. 
In experiment 1 the milk was cooled during a period of 155 minutes 
to about 75° F. (23.9° C.) only, as the outside air was warm, but as 
will be seen from the results the bacterial count was even lower after 
cooling than before. In the other four experiments the milk was 
cooled to below 50° F. (10° C), and the length of the cooling period 
varied from 93 to 150 minutes. It is interesting to note that when 
the bacterial count in the raw milk was high, there was a marked 
reduction in the number of bacteria during the process of cooling 
by forced-air circulation. When the bacterial content of the raw 
