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 hom's. 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 



/ 1 

 \ 2 

 / 1 

 I 2 

 / 1 

 I 2 



i ! 



1 490,000 

 } 128,000 

 i 12,800,000 

 \ 140,800,000 

 1 7,400,000 



/ 5, 400 

 \ 7, 100 

 / 5, 000 

 \ 4, 400 

 / 155, 000 

 \ 156,000 

 / 525, 000 

 \ 555, 000 

 f 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. 1 

 } 155 



} 150 



1 148 



1 127 



1 93 



2 . . . . 



3 



4 .. . . 



5 





• 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 



