THEORIES OF FERMENTATION. 251 



when the juice is kept at a low temperature a marked loss in. 

 its fermentative power is observed in the course of a few days, 

 owing to the influence of endotryptase. It is quite possible 

 that it is this enzyme, more strongly developed, which attacks 

 the enzyme of the yeast cells when they are exposed to un- 

 favourable conditions. Buchner certainly believes that this- 

 accounts for the fact that yeast- juice prepared from one and 

 the same species of yeast may contain very variable quantities 

 of zymase. Zymase is extraordinarily sensitive both to 

 variations in temperature and to the presence of strong alkalies. 

 To protect the juice from the action of endotryptase large 

 additions of cane sugar have been employed. Thus when 

 mixed with 75 per cent, sugar solution the activity of the 

 enzyme has been prolonged for several weeks. 



As a result of a number of fermentations, Buchner notes 

 that the fermentative power of 20 c.c. of yeast-juice with the 

 addition of 8 grammes of sugar and 0-2 c.c. of toluol results 

 in a yield of 1-87 grammes of carbon dioxide. 



Compared with the fermentative power of fresh yeast, the 

 action of the juice appears trifling. Thus, 1 gramme of good 

 pressed yeast produces in an 8 per cent, cane-sugar solution 

 1-5 grammes of carbon dioxide in six hours at 30 C., whilst 

 20 c.c. of yeast-juice is produced from about 40 grammes of 

 yeast, but it should not be forgotten that during the fermenta- 

 tion with living cells new zymase is constantly being produced, 

 and that by no means all the existing zymase is extracted from 

 the cells in the preparation of the juice. 



To avoid the rapid decomposition of the juice, it may be 

 dried in a vacuum at 25-35 C. It forms a yellowish powder, 

 which remains unchanged for a long time, and when dissolved 

 in water displays an almost undiminished fermentative power. 



In contrast to the action of weak alkalies, the addition of 

 acid is prejudicial to the juice. 



With regard to the best conditions of temperature, it has- 

 been shown that the highest fermentative activity is reached 

 at 12- 14 C. The most favourable temperature for zymase 

 undoubtedly lies higher, but it must be remembered that at 

 the higher temperature endotryptase immediately comes into* 

 action and attacks zymase. 



