14 



BULLETIN 202, U. S. DEPARTMENT OF AGRICULTURE. 



INFLUENCE OF THE ACTION OF RENNET. 



The relation of the alcohol test to the acidity of milk shows that 

 acidity is one factor which may cause a positive alcohol reaction, 

 but from the work of other investigators it is evident that it is not 

 the sole cause. Morres throughout his papers points out that the 

 alcohol test may be caused by an acid fermentation or by a rennet 

 fermentation or by a mixture of both fermentations. 



In order to determine the effect of rennet action in relation to the 

 test, we first tried the effect of prepared rennet. Four flasks of fresh 

 milk were used and to each a different percentage of rennet was 

 added. The milk in each flask was tested by the alcohol test at 

 intervals of one hour. It will be seen from Table 10 that four 

 different percentages of rennet were used, ranging from 0.00005 per 

 cent to 0.0015 per cent. The acidity of the milk increased during 

 the four hours from 1.64 to 1.70; therefore the influence of acidity 

 can be neglected, since it is only a slight change. 



The results show that the action of rennet in milk may produce 

 changes which cause a positive alcohol test and that two main factors 

 are of importance, namely, the amount of rennet and the length of 

 time the rennet has to act. Undoubtedly a third factor must be 

 taken into consideration; that is, the temperature at which the milk 

 is held. In our experiments the milk was held at room temperature. 

 These results confirm those obtained by other investigators and 

 indicate that the action of the rennet-forming bacteria might cause 

 a positive alcohol reaction. 



Table 10. — Influence of rennet on the alcohol test. 



Hours. 



Rennet 

 added. 



Alcohol test. 



75 per 

 cent. 



68 per 

 cent: 



44 per 

 cent. 







1 

 2 

 3 



4 



Per cent. 

 .00005 

 .00025 

 .0005 

 .0015 

 .00005 

 . 00025 

 .0005 

 .0015 

 .00005 

 .00025 

 .0005 

 .0015 

 .00005 

 .00025 

 .0005 

 .0015 

 .00005 

 .00025 

 .0005 

 .0015 



i +M 



+ M 

 + L 



+M 

 + M 

 + L 



+ L 

 + L 

 ( 2 ) 



+ M 



+ M 

 + L 



+M 

 + M 

 + L 



+ L 

 + L 

 ( 2 ) 



+ M 



+ M 



L 



+VS 

 ( 2 ) 



1 See footnote under Table 1. 



2 Milk curdled by rennet. 



