2<5O 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 0.4 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 usually greater than is indicated by this 

 rule. (See p. 12). 



The above rule is based upon work done in making 

 a careful study in New York State of the milk of each 

 of 50 different herds of cheese-factory cows during one 

 season (May to October). Taking the average of the 

 entire season it was found that 80 per cent, of the 

 results obtained by the method of calculation differed 

 from those given by the chemical method by less than 

 o.i per cent. 



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. 



The rule will be found useful by physicians in modi- 

 fying milk for infant feeding. 



