FROM THE PRACTICAL VIEWPOINT 



It is also doubtless true, however, that with some 

 types of apparatus in use by the milk dealers and 

 with some conditions under which milk is handled, 

 a real difficulty is experienced in obtaining satis- 

 factory results. 



The chart shown in Fig. 34, drawn by Dr. North, 

 indicates graphically the temperatures and holding 

 times within which it is safe to heat milk without 

 affecting the cream line. Such a chart cannot show 

 the other factors which also affect the results, such 

 as the amount of agitation, etc. 



If the milk is being heated and an attempt is 

 made to keep the milk at a temperature no lower 

 than 145 F it is almost certain that the tempera- 

 ture will at times reach from 146 to 148 or higher,, 

 and that it will at times be held longer than thirty 

 minutes. It is almost mechanically impossible to 

 so control the temperature of milk while heating 

 that there will not be considerable variation. 



The agitation probably has the effect of break- 

 ing up the fat globules into smaller masses. Since 

 each globule of fat is surrounded with a film of 

 casein or skim milk, which is heavier than the fat, it 

 is evident that as the mass of fat becomes smaller, 

 the proportional amount of the surrounding skim 



229 



