So8 MICROBIOLOGY OF SPECIAL INDUSTRIES 



they may be present in sufficient quantities to spoil the grapes before 

 they are gathered. On sound grapes which are gathered and handled 

 carelessly, they may develop sufficiently before fermentation to injure 

 or spoil the wine. 



An exception to the generally harmful effect of these molds is , 

 Botrytis cinerea {Sclerotinia fuckeliana) which under certain circum- 

 stances may have a beneficial action. When the conditions of tem- 

 perature and moisture are favorable, this mold will attack the skin of 

 the grape, facilitating evaporation of water from the pulp. This 

 results in a concentration of the juice. The mycelium then penetrates 

 the pulp, consuming both sugar and acid, principally the latter. The 

 net result is an increase in the percentage of sugar and a decrease in 

 that of acid. This, where grapes ripen with difficulty, is an advantage, 

 as no moldy flavor is produced; Two harmful effects, however, follow: 

 the growth of the mold results in the destruction of a certain amount of 

 material, and a consequent loss of quantity, which is, in certain circum- 

 stances, more than counterbalanced by an increase in quality (wines 

 of the Rhine, Sauternes) ; again, an oxidase is produced which tends to 

 destroy the color, brightness and flavor of the wine. This can be 

 counteracted by the judicious use of sulphurous acid. 



Yeasts. — The true yeasts occur much less abundantly on grapes 

 than the molds. Until the grapes are ripe they are practically absent, 

 as first shown by Pasteur. Later, they gradually increase in number 

 and on very ripe grapes often become abundant. In all cases and at all 

 seasons, however, their numbers are much inferior to those of the molds 

 and pseudo-yeasts. The cause of this seems to be that in the vineyard 

 the common molds find conditions favorable to' their development at 

 nearly all seasons of the year, but yeasts only during the vintage 

 season. 



Investigations of Hansen, Wortmann and others show that yeasts 

 exist in the soil of the vineyard at all times, but in very varying amounts. 

 For a month or two following the vintage, a particle of soil added to a 

 nutritive solution contains so much yeast that it acts like a leaven. For 

 the next few months, the amount of yeast present decreases until a 

 little before the vintage, when the soil must be carefully examined to 

 find any yeast at all. As soon as the grapes are ripe, however, any 

 rupture of the skin of the fruit will offer a favorable nidus for the 

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



