DAIRYING 



79 



Plate 33. A type of beer-pasteurizing machine adaptable to the 

 pasteurization of milk in bottles. 



804. If a clean milk from healthy cows is to be pasteurized 

 and there is no danger of its being contaminated with the spores 

 of putrefactive bacteria or the germs of the tuberculosis bacillus, 

 or other disease germs, then the temperature and the length of 

 time of heating may be greatly reduced, as the lactic acid bacteria 

 are destroyed at near 130 degrees F. and heating to this tempera- 

 ture will greatly increase the length of time that such milk will 

 keep sweet. If, however, on the other hand the milk supply is 

 obtained from many farms, that are never inspected and about 

 which little or nothing is known, it may contain many spores of 

 the putrefactive bacteria and an unknown variety of disease 

 germs. Such milk as this may often be rendered less harmful by 

 pasteurization, provided it is heated while the milk is still sweet, 

 but after pasteurization it will only keep sweet a limited length 

 of time because the spores are so numerous that they are not 

 likely to be all destroyed by the heating. The longer the period 

 of heating, the greater will be the number of spores destroyed 

 and on this account the intermittent process of pasteurization is 

 best adapted to the handling of mongrel milk. 



