i 4 CLEAN MILK 



which the milk may be retained for the required time, at the proper 

 temperature, are preferable. 



Almost all the commercial pasteurizers are of the continuous 

 type, for convenience in handling large quantities of milk, and are 

 made to allow milk to flow through them as quickly as possible, 

 after the temperature of the milk has been raised to 155 F., 

 165 F., or thereabouts. A discontinuous pasteurizer, in which the 

 milk is heated by a hot water jacket while it is kept in motion by 

 rotating arms or other device, is to be preferred because the milk 

 may be kept in the machine for the proper time after it has reached 

 the desired temperature. 



When milk is to be used directly for food it is better that it 

 be pasteurized in sterile bottles so that it may not become afterward 

 contaminated by handling. 



The bottles are first cleaned and sterilized, and filled and 

 capped, and then placed in a steam sterilizer; or are immersed to 

 their necks in a water bath heated by steam. All milk should be 

 rapidly cooled after pasteurization. If in bottles, the water about 

 the bottles is quickly reduced in temperature. If milk is heated and 

 unstirred in open vessels a scum will form on the surface in which 

 the germs of tuberculosis may not be killed by ordinary pasteuriza- 

 tion temperature and time. The cost of pasteurization is said to 

 be from 1/10 to y 2 cent per quart. Rapid alteration in temperature 

 is particularly effective in killing bacteria. So that, in the short 

 pasteurization done commercially, rapid cooling is of the greatest 

 import. Rapid cooling also destroys the cooked taste of milk. 

 Pasteurized milk should not only be immediately cooled to 40 F., 

 after heating, but should be kept at that temperature in closed, ster- 

 ilized bottles or cans for several hours before it is delivered — to 

 still further check the growth of bacilli. 



In order that a pasteurizer shall fulfil the scientific require- 

 ments it must be able to heat the entire amount of milk it contains 

 (including the froth) to the proper temperature, and maintain the 



