484 BUTTER 



Thus the use of rusty utensils on the farm, the holding and 

 shipping of the cream in rusty cans, the use of forewarmers, 

 pasteurizers, coolers, vats, pipes and conduits, etc., in which 

 the copper has become exposed and especially where the cop- 

 per surface is not scoured thoroughly and regularly and is per- 

 mitted to accumulate verdigris, furnishes a logical basis for the 

 development of metallic flavor. 



Both iron and copper are most active in the presence of 

 acid forming metallic salts. Therefore, this flavor defect occurs 

 most prominently in butter made from cream that reaches the 

 creamery in sour condition and is churned sour. Because of 

 this fact, metallic flavor is generally more prevalent and more 

 pronounced in summer than in winter butter, the cream con- 

 taining more acid during the hot weather than during cold 

 weather, although metallic flavor is by no means confined to 

 summer butter, and may appear at any time of the year. 



Flash pasteurization, combined with the use of the sur- 

 face coil cooler for cooling the heated cream, further invites 

 metallic flavor, partly because the action of the sour cream in 

 the presence of heat, air and light on the metal surface of the 

 cooler, is intensified, and partly because this method of cool- 

 ing may result in oily butter, which is often a forerunner or 

 preliminary stage of metallic flavor. 



For similar reasons, rich cream (cream testing over 33% 

 fat), and cream that is excessively diluted with water, tends to 

 cause butter to develop metallic flavor. As explained under 

 "Oily flavor," such cream contains a relatively low per cent of 

 solids not fat and its viscosity is slight. This robs the cream 

 of the protecting influence of the solids not fat, the fat globules 

 are subjected to excessive mutilation during flash pasteurization 

 and yield more readily to the oxidizing influence of heat, air and 

 light, to which they are exposed, while the hot cream runs over 

 the surface cooler. 



The ripening and holding of the sour cream in the copper 

 vats and similar equipment for a prolonged period of time, 

 such as holding it over night in vats with profusely exposed cop- 

 per, may lend additional impetus to the development of metallic 

 and similar off-flavors in butter, accelerating the action of the 

 acid on the metal, and the oxidizing and catalizing action of 



