94 MANUAL OF MILK PRODUCTS 



we may reasonably expect that it is causally connected in some 

 way with this microscopic appearance. 



To prove this point more conclusively, it is necessary to study 

 simultaneously, both from a microscopical and a viscometrical 

 standpoint, milks that have been heated at different tempera- 

 tures. 



Experiments on this point were made, showing that the change 

 in consistency did occur at practically the same temperature at 

 which the microscopic clots in the milk broke down. This 

 relation seems to show that the greater consistency of natural 

 cream is very intimately connected with the presence of these 

 fat aggregations. In milk this is less pronounced, owing to the 

 greater effect that the serum solids have upon the total con- 

 sistency of the fluid. 

 Centrifugal force. 



It is a well-known fact to creamery men that cream taken 

 from milk by the centrifugal cream separator is considerably 

 thinner than that containing the same percentage of fat that 

 is obtained by the gravity system. The cause of this has not 

 yet been satisfactorily explained, but is generally attributed to 

 the higher temperature and the fresher condition of the milk 

 in the separator process. 



A comparative microscopical examination of separator and 

 gravity creams throws much light on this question. In every 

 case the tendency toward grouping is greatly reduced in the 

 separator cream, the fat globules often being as homogeneously 

 distributed as in pasteurized cream. Frequently groups of 

 globules are observed in separator cream that are due to incip- 

 ient churning. These, however, can be readily distinguished 

 from the normal fat aggregation because the globules are almost 

 always distorted or coalesced. The thickening of cream in the 

 churn is also probably due to something of this sort. 



