216 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
ing apparatus are in use. In all of those used in the 
“flash” and “holder” method, the milk is exposed in some 
way to surfaces heated by hot water or steam. Hot 
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Fia. 24.—A pasteurizer of simple type (B. A. I. Circe. 184). 
water is best; it maintains the heating surfaces at a 
more even temperature and the milk is less likely to be 
scorched than when steam is used. To meet the neces- 
sary requirements, a pasteurizer must heat all of the 
