PASTEURIZATION. 



177 



an uncommon occurrence to have the heating wall of a pasteur- 

 izer burst. This could be prevented by connecting a safety, or 

 pressure, valve, to the pasteurizer. 



(2) Degree of Adhesiveness. — 'Rou^ness, due to either 

 defects in the metal itself, or to milk or cream being burned 

 on the heating-surface, is a serious defect. Such a condition 



Fig. llT.^The Simplex regenerative pasteurizer (apart). 



causes particles of milk or cream to move very slowly over the 

 heating-surface; it tends to I'oU in much the same way as 

 drops of liquids do when caused to flow over a slanting dry 

 rough surface. As a consequence more and more casein will 

 adhere. The thicker the layer of foreign matter is on the 

 heating-surface, the greater the difficulty in getting the greatest 

 efficiency from the pasteurizer. 



It is important that the milk or cream be forced over the 

 heating-surface with greater rapidity than could result from 

 its own gravity. On heaters or pasteurizers, where milk flows 



