Non-Saccharomyces yeasts in wine production

Wine fermentations, as conducted by traditional methods (without inoculation), are not the result of the action of a single species or a single strain of yeast. Rather, the final products result from the combined actions of several yeast species, which grow, in succession throughout the fermentation process. Some studies have described the isolation and identification of yeasts from grape surfaces, and quantitative data on the ecology of grape yeasts have concluded that the isolation process of the total yeast population from the grapes is complex and dependent on many factors. Fermentations are initiated by the growth of various species of Candida, Debaryomyces, Hanseniaspora, Hansenula, Kloeckera, Metschnikowia, Pichia and Torulaspora. Their growth is generally limited to the first two or three days of fermentation, after which they die off. Subsequently, the most strongly fermenting and more ethanol tolerant species of Saccharomyces take over the fermentation. It is believed that during the first step of the fermentation low-fermentative yeasts produce some important reactions in must, which improve the final flavour of wines.