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REPORT OF THE CHEMICAL DEPARTMENT. 
CHEMICAL CHANGES IN THE SOURING OF MILK AND 
PEER RELA IONS 10; COTTAGE, CHRESE.* 
L. L. VAN SuyKeE AND E. B. Hart. 
SUMMARY. 
1. Purpose of the Work.—The purpose of the wark discussed 
in this bulletin was to learn the amounts of casein monolactate 
and casein dilactate that are formed in the ordinary souring of 
milk, and to consider the results in some of their practical appli- 
cations to the manufacture, ripening and digestibility of cottage, 
or Dutch, cheese. 
2. Chemical Changes in Sowring of Milk.—(1) Decrease of 
milk-sugar. The loss of milk-sugar increased quite rapidly for 
32 hours at room temperature (65° to 80° F., 18° to 27° C.), after 
which the change was small and in 72 to 96 hours ceased, when 
the maximum loss of milk-sugar was reached, 1.50 per ct., 
equivalent to about 28 per ct. of the sugar originally present 
in the milk. (2) Amount of lactic acid formed. The maximum 
amount of lactic acid formed was about 0.90 per ct., which is 
equivalent to about 62 per ct. of the milk-sugar that disap- 
peared. (3) Coagulation of milk in relation to acid. , At the 
temperatures used, the milk coagulated in 24 to 2914 hours, when 
the percentage of total acid shown by titration had reached 0.6 
to 0.7. (4) Formation of casein monolactate and casein dilactate. 
When the milk was first visibly coagulated, 18 to 14 per ct. of 
the casein was in the form of monolactate and 86 to 87 per ct. 
was in the form of dilactate. With further increase of acid in 
the milk, the monolactate passes into the dilactate. 
* Reprint a Bulletin No, 245, 
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