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REPORT OF THE CHEMIST OF THE 
THE PROTEIDS OF BUTTER IN RELATION TO 
MOTTLED BUTTER.* 

L. L. VAN SLYKE AND E. B. HArt. 
SUMMARY. 
1. Points investigated.—The questions studied in this bul- 
letin are: (1) The relation of casein compounds to cream-ripen- 
ing; (2) casein compounds present in butter and buttermilk; (3) | 
the relation of casein compounds to mottled butter. 
2. Casein compounds in ripened crcam.—In ordinary methods 
of cream-ripening, neither calcium casein nor free casein is present, 
but only casein lactate, when the lactic acid is allowed to exceed .5 
per ct. Casein lactate is the substance most familiar as curdled 
sour milk. 
3. Casein compounds in butter and buttermilk.—When the 
amount of lactic acid in cream exceeds .5 per ct., the casein in 
the butter and buttermilk is present as casein lactate. In butter 
and buttermilk made from so-called sweet cream, we usually find 
calcium casein and some free casein, and on standing for some 
weeks these may be changed in the butter into a mixture of free 
casein and casein lactate or wholly into casein lactate. : 
4. Views commonly held in respect to cause of mottled butter.— 
It has been quite universally believed that the light spots or 
streaks in butter, known as mottles, are caused by the uneven 
distribution of salt, the more concentrated brine deepening the 
yellow color of the fat, and the lighter portions being the unsalted 
or lightly salted areas. 
5. Points studied in relation to mottled butter.—The investiga- 
tion covered the following conditions in relation to the mottling - 
of butter: (1) Richness of cream, (2) degree of ripeness of cream, 
(3) temperature of churning, (4) size of butter-granules, (5) 
temperature of wash-water, (6) working of butter. 


*A reprint of Bulletin No. 263. 
