New York AGRICULTURAL EXPERIMENT STATION. 101 
CHANGE OF INSOLUBLE INTO SOLUBLE NITROGEN COMPOUNDS IN COT- 
TAGE CHEESE. 
In Bulletins 234 and 236 of this station, we have shown to what 
extent the insoluble nitrogen compounds of new cheddar cheese 
change into soluble forms during the process of ripening. While 
Dutch cheese is made to be eaten fresh or within a few days 
after its preparation, and is not expected to undergo a period of 
ripening like cheddar cheese, we desired to learn to what extent 
such digestive changes might occur in cottage cheese. For this 
purpose, seven lots of cottage cheese were made under different 
conditions. In every case we used 30 pounds of milk and, except 
in experiment 1, one-half pound of sour-milk starter. The sam- 
ples of cheese were all kept in an atmosphere of chloroform to 
prevent the action of organisms, and at a temperature of 60° F. 
(15.5° C.). The milk used was separator skim-milk, pasteurized 
in experiments 2 and 6 and unpasteurized in exneriments 3 and 7, 
and whole milk in experiments 1, 4 and 5. In experiment 1, the 
milk, 2 hours old, was coagulated by 0.4 per ct. of lactic acid 
in the presence of 3 per ct. of chloroform. In experiments 2, 3 
and 4, the milk was allowed to sour naturally at room tempera- 
ture except that a starter was added, while in experiments 5, 6 
and 7, 0.5 cc. of Hansen’s rennet extract was used in addition to 
the starter 8 hours after the starter was added. When rennet 
was used the milk was allowed to stand 48 hours, after which 
the temperature was raised to about 100° F. (88° C.) for 15 
minutes in order to cause separation of whey. From the results 
of some of our work, it appears that milk to which rennet has 
been added appears to form acid less rapidly. Hence, it is well 
to let the formation of acid get well started before adding rennet. 
This can be done by waiting about 8 hours before adding rennet. 
The special conditions used in preparing the different lots of 
cheese are stated in tabular form as follows: 
TapLeE VII.—SHowine Conpitions Usep IN PREPARING CHEESE 
FoR PROTEOLYTIC SrupDy. 
| 
= | Temp. at 
| Amount} Temp. which 
No. of Amount | ofren- | of milk whey Water in 
experi- KIND OF MILK USED | of starter | net | while | separated | cheese. 
ment. used. extract | souring. from 
| used. eurd. 
| | 
Pounds. Ce. Deg. F. | Deg. F. Per ct 
1 Whole. Not pasteurized... 0. 0. 75 71.07 
2 Skim. Pasteurized........ OD 0. 7D) 90° | 81.40 
3 Skim. Not pasteurized... . 0.5 oO. | | 90° 78.60 
4 | Whole. Not pasteurized... 0.5 Oo.) 75 | 10425) fore0 
5 Whole. Not pasteurized... 0.5 | ONS rae) 106° | 74.20 
6 Skim. Pasteurized........ 0.5 0.5 | 75 98° 72.05 
@ Skim. 4 Not pasteurized.... 0.5 0.5 vol 98° 68.00 
