CREAM 335 



and a pleasant odour or aroma ; to what these latter 

 characters are due is not known with certainty. Since 

 it is. found that lactic bacteria alone cannot properly 

 ripen cream, it is probable that aromatic compounds of 

 an agreeable flavour are produced by the action of 

 bacteria allied to the putrefactive organisms upon the 

 proteins of the serum, these being absorbed by the fat 

 and transferred ultimately to the butter. 



Very little, if any, chemical changes occur in the fat, 

 but its physical characters are altered by ripening and 

 ripened cream churns more quickly than sweet cream ; 

 it also gives up more of its fat in the form of butter, and 

 less of the fat remains in the buttermilk than when sweet 

 cream is used. 



The exact nature of the change in the fat which 

 enables the globules to coalesce readily when shaken in 

 the churning process is not understood. 



Some authorities have put forward the view that the 

 globules are surrounded by a film of protein, which is 

 dissolved or decomposed during ripening, thus allowing 

 easy amalgamation of one globule with another. It is, 

 however, more likely that the phenomenon is connected 

 with alterations in the viscosity and surface tension of 

 the serum. 



Ex. 152. Mount a drop of cream on a slide, and examine 

 with a and J in. objective. 



Compare the number and appearance of the fat globules with 

 those of a similarly mounted drop of skim-milk. 



As previously mentioned, unripened cream contains 

 from J to 6 millions of organisms per c.c. ; in the 

 ripened product from thirty-six to forty-eight hours old, at 

 which period the bacteria reach their maximum develop- 



