EXPERIMENT STATION BULLETINS. 



421 



TABLE IV. 

 Add Reduction by Pure CtUturee of Yeafts— Demonstrated bj Growth in Arliflcially Acid Whey, 



♦Contaminated, titrations discontinued. 



Fi'om Tables VI, VII, and XI following, it will be noted that a similar 

 acid reduction takes place in the mixed cultures. 



In each of the different flasks of the yeast LZ no signs of growth 

 were noted until after the 4th day and none in the flask of -|-90° whey 

 until after 20 days. The following curve illustrates the comparative 

 acid reduction of the different yeasts. This curve is constructed from 

 the data in Table IV. 





Comparative Acid Consumption or 4 Yeasts 



CROWING IN ACID WHEY. 



\ 



\ 



\ Red Yeast'- Scum Yeast •■• Butter Veastrr" 



\ 



Wh«y Yeast — 





«CpntdTninated 



Curve I. 



Yeast DR, the scum yeast from brine pickles, is much more active 

 in reducing acid than any of the other yeasts; j-east SC is second in 

 activity, yeast DG third, while yeast LZ is much the weakest. From 

 these curves it would appear that the function of yeast LZ is not prin- 

 cipally that of acid reduction ; this seems to be of secondary importance. 

 It will also be noted that in most cases the acid-reducing function of 

 the yeast LZ is evident only after about 8 days, it then continues to act 

 with greater or lesser rapidity as the amount of acid present in the 

 medium is large or small. The time of the beginning of acid reduction 

 in the pure culture of yeast LZ corresponds quite exactly with the 

 period in the life of ordinary lactic organisms at which the bacterial 



