Milk and Its Products. 285 



cess," or "aerated" butter. This is done by melting the butter, 

 separating the fat from the casein, water, etc., blowing air 

 through the fat to remove the unpleasant odors, and then churn- 

 ing the liquid fat with milk until an emulsion is formed. This 

 is then quickly cooled in ice and a granular mass results. It is 

 then worked, salted, and made up as butter. 



Oleomargarine is also known as " margarine" or "butterine. " 

 This product, which is intended as a substitute for butter, is 

 made by churning so called ' ' oleo oil ' ' with lard, milk, sometimes 

 a little butter, and occasionally cotton-seed oil or peanut oil, in 

 a warm state. After the churning the mixture is quickly cooled, 

 salted and "worked." Where coloring matters are used, with 

 the intention of imitating butter, a tax of 10 cents a pound is 

 imposed. On uncolored "oleo" a tax of % cent per pound is 

 levied. 



The "oleo oil" is made from beef fat by melting, carefully 

 clarifying, and allowing it to stand at a temperature of about 

 30 C. The semi-solid mass which results is then separated by 

 a press into solid stearin and a liquid composed of olein and 

 palmitin. 



Pure butter can be distinguished from "renovated" butter 

 and from "oleo" by its behavior when heated in a test tube or 

 spoon over a flame. Oleomargarine and renovated butter boil 

 with much sputtering and produce no foam, or very little, while 

 genuine butter in boiling produces more foam and less noise. 



Butter-milk. The liquid remaining in the churn after the 

 separation of butter from the cream varies a good deal in com- 

 position. With good churning of ripened cream, the percentage 

 of fat in the butter-milk may be 0.3 or less. When sweet cream 

 is churned 1.0 per cent of fat may be expected. The average 

 composition of butter-milk will be about as follows: Water, 

 90.9 per cent ; proteins, 3.5 ; fat, 0.5 ; sugar and lactic acid, 4.4 ; 

 ash, 0.7. The chief use for butter-milk has been as food for pigs, 

 but there is a growing demand for it as human food. The finely 



