278 



SCIENCE AND PRACTICE OF DAIRYING. 



tion of Pasteurized milk, but rennet and butyric acid bacteria. In 

 such cases the coagulated milk exhibits only a slightly weak acid 

 reaction, and shows near the surface a thin whey-like layer. If 

 the creaming be effected, as is now beginning to be customary, by 



centrifugal force at 75 C., 

 and the milk be kept 

 fifteen minutes at this 

 temperature, the cream is 

 obtained, as well as the 

 skim -milk, in the same 

 condition as ordinary Pas- 

 teurized milk. If the 

 creaming operation be 

 followed at the tempera- 

 ture which is now cus- 

 tomary, of 25 to 35 C., 

 the skim-milk is often 

 Pasteurized (fig. 78) in 

 order to impart the neces- 

 sary keeping qualities to 

 it, and to permit of its 

 regular transport to other 

 places. Cream for butter- 

 making should only be 

 slightly Pasteurized if it 

 be intended to be kept for 

 a few hours only, or if it be 

 intended to be soured with 

 a pure culture of lactic 

 ferment for the purpose 

 of being made into butter. 



Fig. 79. Pasteurizing Apparatus (Burmeister <fe Wain). 



At the present time twelve different Pasteurizing apparatus for milk are 

 known. The whole of the apparatus (figs. 79 and 80) have this in common, 

 that the milk is stirred by metal paddles, which are heated by steam or 

 boiling water. They are brought up as quickly as possible to the tempera- 

 ture of 65 to 80 C., and have an uninterrupted flow of milk passing 

 through them. They may be divided into classes, viz. those in which the 

 milk flows out over a ribbed hot-plate, and those in which the heated 

 milk flows through differently constructed closed spaces. All apparatus, 

 without exception, suffer from two defects. The first consists in the 



