606 MICROBIOLOGY OF ALCOHOLIC FERMENTATION 



development and increase of any yeast cells which reach it. Where 

 these first cells come from has not been determined, but as there are 

 still a few yeast cells in the soil, they may be brought by the wind, or 

 bees and wasps may carry them from other fruits or from their hives 

 and nests. 



The increase of the amount of yeast present on the ripe grapes is 

 often very rapid and seems to have (according to Wortmann) a direct 

 relation to the abundance of wasps. These insects, passing from vine 

 to vine, crawling over the bunches to feed on the juice of ruptured 

 berries, soon inoculate all exposed juice and pulp. New yeast cultures 

 are thus produced, and the resulting yeast cells quickly disseminated 

 over the skins and other surfaces visited. 



The more unsound or broken grapes present, and the more honey- 

 dew or dust adhering to the skin, the larger the amount of yeast will 

 be. The same is true, however, also of molds and other organisms. 



In the older wine-making districts, much of the yeast present on the 

 grapes will consist of the true wine yeast, S. ellipsoideus. The race or 

 variety of this yeast will differ, however, in different districts. Usually 

 several varieties will be found in each district. The idea prevalent at 

 one time, that each variety of grapes has its own variety of yeast seems 

 to have been disproved, though there seems to be some basis for the 

 idea that grapes differing very much in composition, varying in acidity 

 and tannin contents, may vary also in the kind of yeast present. 

 Several varieties of S. ellipsoideus may occur on the same grapes. In 

 new grape-growing districts, where wine has never been made, S. 

 ellipsoideus may be completely absent. 



Besides the true wine yeast, other yeasts usually occur. The com- 

 monest forms are cylindrical cells grouped as S. pasteurianus. These 

 forms are particularly abundant in the newer districts where they may 

 take a notable part in the fermentation. Their presence in large 

 numbers is always undesirable and results in inferior wine. Many 

 other yeasts may occur occasionally and are all more or less harmful. 

 Some have been noted as producing sliminess in the wine. Many of 

 these yeasts produce little or no alcohol and will grow only in the 

 presence of oxygen. 



Pseudo-yeasts. Yeast-like organisms producing no endospores 

 always occur on grapes. Their annual life-cycle and distribution are 

 similar to those of the true yeasts, but some of them are much more 



