364 BOARD OF AGRICULTURE. [Pub. Doc. 



The object of holding the milk or cream at this temperature 

 is to destroy or render harmless for a considerable time the 

 various bacteria contained in the milk, thus preserving it 

 from decomposition. Heating at this temperature, while it 

 kills or renders harmless the bacteria, does not destroy the 

 spores. This destruction of bacteria increases the keeping 

 quality of the milk or cream by several days 



If it is desired to ripen cream for butter making by any 

 special ferment, the pasteurization of the cream, even for a 

 few minutes, so overpowers or partially destroys the ordinary 

 bacteria of the cream, that the special bacteria introduced 

 have opportunity to become thoroughly developed. 



Sterilization of milk or cream means the heating of it to 

 boiling or even above the boiling point by aid of pressure. 

 This not only destroys the bacteria, but the spores as well, 

 although for a complete destruction of the spores more than 

 one heating is necessary. The so-called Dahl process for 

 making perfectly sterilized milk consists in heating the milk 

 to 158° F. for three-quarters of an hour, then cooling to 

 104° F. for the same time, then heating to 175° F., and 

 finally cooling and placing in sterilized vessels. The object 

 of heating to 104° F. and holding at this temperature for 

 three-quarters of an hour is to allow the spores, which were 

 not destroyed by the first heating, to grow. The second 

 heating destroys them. Milk thus treated has been kept 

 perfectly sweet for a long time. 



Details to be observed in Pasteurizing. — The milk intro- 

 duced into the pasteurizing apparatus should be heated as 

 rapidly as possible to 150° or 155° F. and held at that tem- 

 perature from twenty to thirty minutes. During the heating 

 it should be constantly stirred, to prevent burning on the 

 sides of the vessel. At the expiration of the time, the milk 

 should be rapidly cooled to 50° or 60° F. and then drawn off* 

 into sterilized bottles or cans, the covers put on at once, and 

 placed in ice water. The bottles can be cleaned by the use 

 of some form of bottle cleaner now on the market. This is 

 to be preferred to the use of chemicals. After washing they 

 should be placed in boiling water for ten minutes, and then 

 placed upon racks, mouths downward, to drain. A better 

 way is to use a sterilizing oven (a jacketed oven surrounded 



