158 PROTECTION OF THE .CONSUMER. 



through even more readily. Filtering thus renders the milk 

 more appetizing, but not more wholesome or less dangerous. 



APPLICATION OF HEAT. 



Heat may be employed to destroy bacteria and, if it is 

 properly applied, it will kill all bacteria. The possibility of 

 its use for the purpose of purifying milk is modified by the 

 action of the heat upon the milk itself. In considering the 

 applicability of heat for this purpose we must bear in mind 

 the several purposes which it may be desired to accomplish. 

 It may be the purpose : 



1. Simply to destroy the strictly pathogenic bacteria so as 

 to remove the danger of milk epidemics. 



2. To destroy other bacteria so that the milk will be pro- 

 tected from souring or from other fermentative processes. 



3. To destroy or reduce the bacteria which are associated 

 with the indefinite class of intestinal troubles which are 

 attributed to milk. 



4. To remove the bacteria so as to leave a free field for the 

 action of other bacteria to be inoculated, as in the use of pure 

 cultures. 



Sterilization. A sufficiently high temperature destroys all 

 bacteria and, of course, accomplishes all these purposes at 

 once. But to do this requires a temperature so high that it 

 produces certain changes in the nature of the milk. It cooks 

 the milk, and the feasibility of the process depends upon the 

 nature and significance of these changes. Since some of the 

 common milk bacteria are spore-producing forms which 

 resist high heat, to destroy them completely requires a heat 

 higher than that of boiling water. To accomplish such a 

 sterilization it is necessary to heat milk in closed vessels under 

 a steam pressure sufficient to give a temperature of several 

 degrees above boiling, the exact temperature being dependent 

 upon the length of time the heating continues. A tempera- 

 ture of 220 F. continued for half an hour is commonly, 

 though not always, sufficient for the purpose. 



