192 MODERN METHODS OF TESTING MILK 



10. FINDING PER CENT. OF CASEIN IN MILK 

 FROM FAT 



Rule. — To find the per cent, of casein in milk when 

 the per cent, of fat is known, subtract 3 from the per 

 cent of fat in milk, multiply the result by .4 and add 

 this result to 2.1. Example: How much casein is there 

 in milk containing 4.5 per cent, of fat? (4.5 — 3)x.4+ 

 2.1=2.70 per cent of casein. 



This rule is based upon the writer's work, showing 

 that milk testing 3 per cent of fat contains an average 

 of about 2.1 per cent of casein, and that the casein in- 

 creases, on an average, .4 per cent, when the per cent.* 

 of milk increases i per cent, above 3. This is especially 

 true of milks ranging from 3 to 4.5 per cent, of fat 

 when the milk is produced at the same stage of lacta- 

 tion. In the later stages of lactation the ratio of ca- 

 sein to fat is greater than is indicated by this rule. 

 (See p. 12.) 



In applying Rule 9, Rule 10 can be used to find 

 the per cent, of casein in milk when only the per cent, 

 of fat is known. For example, how much cheese can 

 he made from 100 pounds of milk containing 4.25 per 

 cent, of fat? By Rule 10, (4.25— 3)x.4+2.i=2.6, the 

 per cent, of casein in the milk. Then by Rule 9, (2.6 

 x2.5)+(4.25xi.i) = ii.i8 pounds. 



The above rule can be used in finding the amount 

 of casein and albumin together, the factor 2.9 being 

 added instead of 2.1. 



