166 STUDIES ON FERMENTATIOX. 



yielding moulds attain that phase of their vegetation in wliieh, 

 when mixed with the juice of grapes, they produce fermenta- 

 tion. 



In the Jura district a peculiar kind of wine, called straw 

 wine {vin de imUlc), is manufactured, which seems to contra- 

 dict what we have said as to the advent of sterility towards 

 the end of winter in the 5'east-germs formed on the surface 

 of preserved bunches of grapes. This sti'aw wine is made 

 of grapes preserved for long after the vintage on straw. Fromi 

 what we have said it might be supposed that fermentation 

 could not occur under these circumstances. We have, in fact, 

 no doubt that it is often really produced by quite different 

 yeast-germs from those which cause fermentation in the 

 vintage gathered in autumn. Fermentation as effected in 

 the manufacture of straw wine is probably due to yeast-dust 

 spread over the utensils of the vine-grower, and derived from 

 the preceding vintage. We have seen (Chap. III. § 6) that 

 yeast may be dried and reduced to powder, and yet preserve 

 its faculty of germination for several months. It would be 

 useful, however, to submit this surmise to the test of experi- 

 ment, and it would be easy to do so provided we took care to 

 crush the grapes so preserved in very clean vessels, previously 

 heated to a temperature of 100° C. (212° F.), having first 

 rejected every bunch containing injured grapes, which might 

 have fermented or given occasion to the development of yeast. 

 Fermentation, we believe, would not then take place. 



Another consequence results from the various facts that we 

 have brought out in relation to the origin of the wine-ferments, 

 which is, that it would be easy to cultivate one or more vine- 

 stocks so that the grapes gathered from them, and crushed 

 to extract their juice, would be unable to ferment spontaneously 

 emn in autumn. For this purpose it would be sufficient to 

 keep the bunches out of contact with particles of dust during 

 the vegetation of the bunches and the ripening of the grapes, 

 and then to effect the crushing in vessels thoroughly freed 

 from germs of alcoholic ferments. Moreover, every fruit and 



