<P> The most common yeast associated with winemaking is Saccharomyces cerevisiae which has been favored due to its predictable and vigorous fermentation capabilities , tolerance of relatively high levels of alcohol and sulfur dioxide as well as its ability to thrive in normal wine pH between 2.8 and 4 . Despite its widespread use which often includes deliberate inoculation from cultured stock , S. cerevisiae is rarely the only yeast species involved in a fermentation . Grapes brought in from harvest are usually teeming with a variety of `` wild yeast '' from the Kloeckera and Candida genera . These yeasts often begin the fermentation process almost as soon as the grapes are picked when the weight of the clusters in the harvest bins begin to crush the grapes , releasing the sugar - rich must . While additions of sulfur dioxide ( often added at the crusher ) may limit some of the wild yeast activities , these yeasts will usually die out once the alcohol level reaches about 15 % due to the toxicity of alcohol on the yeast cells physiology while the more alcohol tolerant Saccharomyces species take over . In addition to S. cerevisiae , Saccharomyces bayanus is a species of yeast that can tolerate alcohol levels of 17 -- 20 % and is often used in fortified wine production such as ports and varieties such as Zinfandel and Syrah harvested at high Brix sugar levels . Another common yeast involved in wine production is Brettanomyces whose presence in a wine may be viewed by different winemakers as either a wine fault or in limited quantities as an added note of complexity . </P>
<P> The most common yeast associated with winemaking is Saccharomyces cerevisiae which has been favored due to its predictable and vigorous fermentation capabilities , tolerance of relatively high levels of alcohol and sulfur dioxide as well as its ability to thrive in normal wine pH between 2.8 and 4 . Despite its widespread use which often includes deliberate inoculation from cultured stock , S. cerevisiae is rarely the only yeast species involved in a fermentation . Grapes brought in from harvest are usually teeming with a variety of `` wild yeast '' from the Kloeckera and Candida genera . These yeasts often begin the fermentation process almost as soon as the grapes are picked when the weight of the clusters in the harvest bins begin to crush the grapes , releasing the sugar - rich must . While additions of sulfur dioxide ( often added at the crusher ) may limit some of the wild yeast activities , these yeasts will usually die out once the alcohol level reaches about 15 % due to the toxicity of alcohol on the yeast cells physiology while the more alcohol tolerant Saccharomyces species take over . In addition to S. cerevisiae , Saccharomyces bayanus is a species of yeast that can tolerate alcohol levels of 17 -- 20 % and is often used in fortified wine production such as ports and varieties such as Zinfandel and Syrah harvested at high Brix sugar levels . Another common yeast involved in wine production is Brettanomyces whose presence in a wine may be viewed by different winemakers as either a wine fault or in limited quantities as an added note of complexity . </P>
where does the yeast in wine come from ( in traditional winemaking )
where does the yeast in wine come from ( in traditional winemaking )
Grapes brought in from harvest
Grapes brought in from harvest