On Expressed Yeast-cell Plasma (Buchncr's " Zymase "}. 257 



Influence of Age of Yeitst on Activity of Juice. In Table II 

 we give some of our results on the influence of the age of the 

 yeast, i.e., the time which elapsed between the time of collection of 

 the yeast in the brewery, and that of pressing and grinding, on the 

 activity of the cell plasma obtained. The same table shows to some 

 extent the influence of sugar concentration on the amount of gas 

 evolved. 



It will be seen that the results are very variable, but that the 

 general tendency is for the activity of the juice to increase to a 

 certain point with the age of the yeast, the maximum being reached 

 about the 3rd or 4th day from collection. After the maximum is 

 reached there is a very rapid decline in the activity of the juice. The 

 variation in the amount of auto-fermentation is not so great, but the 

 tendency of this is to follow the same direction. The results are 

 shown diagrammatically in figs. 1 and 2, the former showing the auto- 

 fermentation and the latter the fermentation in presence of sugar, 

 both when the gas evolved from the auto-fermentation is included and 

 when it is deducted from the total amount. 



FIG. 1. Showing the influence of age of yeast on auto-fermentation after 



4S hours. 



34 



Age of yeast in d&ys. 



This increase up to a certain point of the activity of the juice with 

 the age of the yeast is the reverse of that which takes place with bottom- 

 fermentation yeasts, as described by Buchner and other Continental 

 observers. 



Influence of Storage on Activity of Juice. When the expressed juice is 

 kept even at or below freezing point, its power both i of auto-fermenta- 

 tion and of decomposing sugar rapidly diminishes. 



Influence of Amount of Sugar present. We carried out a series of 



VOL. LXVII. U 



