16 



BULLETIX 240, TJ. S. DEPARTMENT OF AGRICULTURE. 



the amount of infection introduced by placing milk in an infected 

 bottle. It is evident that in only two samples, Xos. 28 and 35, was 

 the infection entirely destroyed. 



Table 5. — Destruction of dottle infection during the process of pasteurization in 



bottles. 



Sample No. 



Raw milk. 



Milk pasteur- 

 ized in clean 

 previously 

 steamed 

 bottles. 



£Sft& l^sasr 



sour milk and 

 filled with 

 raw milk. 



infected 

 bottles. 



24. 

 25.. 

 27 V 

 28.. 

 291 

 .301 

 311 

 351 

 36i 



Bacteria 

 per c. c. 



24, 900 



94,000 

 235, 000 

 176, 000 



97, 000 

 230, 000 

 124, 000 

 190, 000 



38, 000 



Bacteria 

 per c. c. 



570 

 2,200 

 7,600 

 11,400 

 8,350 

 5,500 

 1,500 

 9,300 

 5,600 



Bacteria 



per c. c. 



3,700.000 



3,300,000 



760, 000 



650, 000 



530, 000 



645, 000 



400, 000 



230, 000 



92, 000 



Bacteria 

 per c. c. 



2,090 

 6,200 

 9,500 

 11.000 

 20,000 

 20,900 

 28,600 

 9,600 

 17,700 



1 Bottle infected with old, sour, pasteurized milk. 



It is quite possible that infection from unclean bottles might be- 

 come a serious factor in bottle pasteurization. When one ' considers 

 that in pasteurization in the bottle the bacteria which are left are 

 either heat-resistant vegetative cells or spores, it is easy to see that 

 if a large number are left in a bottle and it is again filled with milk 

 and pasteurization again performed in the bottle these same bacteria 

 will again survive and increase the number left. It is advisable to 

 steam the bottles at least two minutes before filling with milk for 

 pasteurization in the bottles. 



COOLING MILK WHICH HAS BEEN BOTTLED HOT. 



When a water-tight cap is used it is, of course, possible to bottle 

 the milk while hot and cool by submerging in cold water, but experi- 

 ments have been made with a process by which the milk may be 

 cooled in bottles capped with ordinary cardboard caps. Briefly 

 stated, the process consists in exposing the hot bottled milk to an air 

 blast. The air-blast system is used at present in the hardening rooms 

 in ice-cream plants, but, so far as known, this system has never been 

 applied to the cooling of milk. 



Several experiments were tried on a laboratory scale which gave 

 promising results. When a bottle of hot milk is allowed to cool in 

 still air a film of warm air forms about it which can move away only 

 by convection, and. naturally, the cooling process is slow. If some 

 means were provided for moving the film of warm air and forcing 



