110 DAIRY CHEMISTRY 



by the gravity process contains a larger amount of 

 fat. Experiments have shown that the additional 

 fat in the gravity skim milk produces only small 

 additional gains over separator skim milk, the gains 

 being of less importance than the commercial value 

 of the butter fat. Skim milk should not be stored 

 or handled in rusty iron pails or cans, because the 

 small amount of acid present has a solvent action 

 upon metals, and if too much iron zinc or tin is dis- 

 solved in the milk, it has an injurious effect when fed 

 to animals. The handling of skim milk, buttermilk, 

 and whey in unclean ways is frequently the cause 

 of abnormal fermentation and the contamination of 

 dairy products. 



100. Whey Composition, Value, and Use. Whey 

 differs in composition from skim milk by containing 

 less solid matter because of the removal of the casein 

 in cheese making. Average whey contains about 7 per 

 cent of solid matter, the larger portion of which is 

 milk sugar, 5.2 per cent. It also contains the albumin 

 of the milk, which, as previously stated, is not retained 

 in the cheese. There is less ash in whey than in skim 

 milk, due to a portion of the mineral matter combining 

 with the casein and being recovered in the cheese. 



While whey contains less solid matter and proteids 

 than skim milk, it nevertheless has a material feed- 

 ing value. Experiments have shown that two 

 pounds of whey are about equal in feeding value to 

 one pound of skim milk. In general, ten pounds of 

 whey will produce as much gain in live weight of 



