FLAVORS OF BUTTER 169 



" The cream may take up iron in quantities sufficient to 

 affect the flavor from rusty cans or even from the exposed 

 boltheads or other metal parts of the churn. 



" The action of copper is similar but perhaps more 

 intense." 



The writer 1 found that when conditions are favorable 

 bacteria produce the metallic flavor. The most impor- 

 tant factor in the development of this flavor is the acidity 

 of the cream. If very little acid is present, the metallic 

 flavor will rarely develop. Except in buttermilk, a high 

 fat-content of the medium is essential. Of 241 samples 

 of cream in sterilized glass bottles, the metallic flavor 

 was produced in 79 by inoculation with buttermilk 

 having this flavor ; and of 157 samples of cream in steril- 

 ized glass bottles, which were inoculated with individual 

 bacteria, 52 showed metallic flavor. The organism causing 

 this is a member or a strain of the Bacterium lactis acidi 

 group. To prevent the formation of the metallic flavor, 

 the cream should be churned when sweet or when the 

 acidity is low, such as .3 per cent lactic acid or less. 



127. Rancid flavor. Rancidity is a specific flavor 

 of dairy products. It is a term often used erroneously, 

 for most persons confuse it with the strong or stale, or 

 some other " off " flavor of butter. Quoting Brown : 2 

 " By the term ' rancidity ' is meant not simply, as is gen- 

 erally supposed, a development of free acid, though this 

 is the general concomitant of rancidity, but any chemi- 

 cal or physical change in the character of the fat from the 

 normal. , Rancidity, according to the present most 



1 Guthrie, E. S., Metallic Flavor in Dairy Products, Cornell 

 Univ. Agri. Exp. Sta., Bui. 373, 1916. 



2 Brown, C. A., Jr., Contribution to the Chemistry of Butter- 

 fat, Amer. Chem. Soc. Jour., 21, 2, 1899. 



