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 ^ 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 jlavor 

 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 : ^ 

 " 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. 8., 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. Soo. Jour., 21, 2, 1899. 



