Wine Yeast, any of a number of yeasts, mainly from the species Saccharomyces cerevisiae, that are used to ferment fruit juice (usually grape) to produce wine. Approximately 150 different wine yeasts are available from commercial producers; most have been isolated from spontaneous (uninoculated) wine fermentations from around the world. These strains are chosen for their beneficial fermentation and/or flavor profiles, for their ability to ferment specific grape types, or for specific technical reasons, for example, the ability to restart “stuck” fermentations. See fermentation. Although most commercial wine yeasts are S. cerevisiae, some are hybrids between S. cerevisiae and other closely related Saccharomyces species and are similar to the hybrid lager yeast, Saccharomyces pastorianus. Although wine and ale yeasts are both members of the S. cerevisiae species, DNA analyses have shown that wine and ale strains form separate groups that are genetically distinct. Because wines generally contain more alcohol than beers, most wine yeasts tolerate higher alcohol levels than beer yeasts. Wine yeasts, however, are generally not considered good fermentation agents for quality beers because they produce flavors and aromas that are not compatible with typical beer sensory profiles. In addition, the spectrum of sugars that they best ferment (mostly glucose and fructose) is not generally the one that most worts represent. However, high-alcohol tolerant “champagne yeasts” are occasionally used in brewing, mostly by craft brewers and amateur brewers, either when a fermentation is stuck or to fully attenuate a high-gravity fermentation. This is often a method of last resort and an indication that the original yeast was either ill-chosen or not healthy at the time of pitching. The yeast strains referred to as champagne yeasts include the popular Prise de Mousse, used by many craft brewers for bottle conditioning. This yeast is highly active and will tolerate alcohol levels as high as 18%, although like many wine yeasts it is a producer of diacetyl (widely tolerated or even desired in wine), which it will usually reabsorb given proper time and conditions.

See also yeast.