PASTEURIZATION 215 



stroy pathogenic organisms by the "flash" method than 

 by the "holder" method. Pasteurization in the final con- 

 tainer is the best method, because it does not afford any 

 opportunity for the milk to be reinfected. But most 

 of the apparatus constructed to pasteurize milk in bot- 

 tles is rather costly and it is also more expensive to oper- 

 ate than that of the " flash " or " holder " variety. Fur- 

 thermore, the bottles must be tightly sealed, and this 

 requires the use of a cap which is more expensive than 

 the ordinary kind. Space must be allowed for the ex- 

 pansion of the milk when it is heated, consequently the 

 bottles cannot be entirely filled. Larger bottles must 

 therefore be provided or the consumer will receive short 

 measure. The vacant space permits the milk to be 

 shaken about, which may disturb the cream. The cream 

 may also "butter" if the milk is subjected to sufficient 

 agitation while warm. 



The milk should be cooled immediately after pasteur- 

 ization. Sudden cooling following exposure to heat 

 has no effect in destroying bacteria, as was formerly sup- 

 posed, but prompt cooling will retard the development 

 of the bacteria or spores which survive pasteurization. 

 The regulations of the Philadelphia Board of Health 

 require that the milk shall be cooled to 50 F. (10 C.) 

 or below immediately after pasteurization, held at that 

 temperature or below while at the pasteurizing plant, 

 and delivered to the consumer within 24 hours. The 

 requirements of the New York Commission on Milk 

 Standards specify that the milk must be cooled imme- 

 diately to a temperature not exceeding 50 F. (10 C.) 

 and held at that temperature until delivered to the con- 

 sumer. 



Types of Pasteurizers. Various types of pasteuriz- 



