Traditionally, wine is produced by spontaneous fermentation and several yeast species have been reported to be involved in the fermentation. The predominant microorganisms on the grapes vary according to the grape variety, climatic conditions, soil quality, development and physical quality of the grapes, as well as the amount of fungicides applied to the vineyards. Nevertheless, the predominant yeast genera on grapes are reported to be Kloeckera and Hanseniaspora, whereas Saccharomyces cerevisiae is not observed or observed at only very low concentrations on healthy undamaged berries. The yeast genera associated with wine making include Candida, Cryptococcus, Debaryomyces, Dekkera (teleomorphic form of Brettanomyces), Hanseniaspora (teleomorphic form of Kloeckera), Kluyveromyces, Metschnikowia, Pichia, Rhodotorula, Saccharomyces, Saccharomycodes, Schizosaccharomy-ces, and Zygosaccharomyces. Some of these yeast genera are thought to be essential for the wine fermentation, and others are regarded as transient organisms. Due to the low pH and high sugar content of grape juice, a natural yeast selection will take place during spontaneous wine fermentation. At the early stages of the fermentation, yeast of the genera Candida, Hanseniaspora, and Kloeckera will dominate, followed by species of Metschniko-wia and Pichia. The latter stages of the fermentation will be dominated by alcohol-tolerant strains of S. cerevisiae (7).
Within the past decades there has been in wine-making an increasing interest in the use of starter cultures, and today most large-scale productions are carried out with starter cultures of primarily S. cerevisiae. Several different physiological variants of S. cerevisiae have been reported for the production of different types of wine and S. bayanus has been used as a starter culture, especially for wine partially produced at low temperatures (e.g., Sauternes, Tokay, Muscat, and Amarone) (99,100). Recently, genera other than Saccha-romyces have been reported to be beneficial in the production of wine in order to enhance the taste and flavor of the wine (101,102).
Yeasts are involved in the production of several special other types of alcoholic beverages besides wine, including a large number of indigenous alcoholic beverages produced by spontaneous fermentation (9). In most cases, the yeast species responsible for the fermentation is S. cerevisiae. However, yeast species belonging to genera other than Saccharomyces have been reported—for example, for the production of sherry, where a secondary fermentation by so-called flor yeast occurs. At the early stage of the secondary fermentation, the yeast forms a surface film on the top of the wine; several yeast species, including Pichia anomala and Pichia membranifaciens yeast have been reported to be involved in this secondary fermentation. However, during the fermentation a microbial succession takes place, and S. cerevisiae is now believed to be the most important flor yeast for sherry production (103). Non-Saccharomyces yeasts have been reported to be especially involved in the early stages of indigenous, spontaneously fermented beverages (104). But at the later stages of the fermentations, S. cerevisiae will practically always dominate, as is the case in the brewing of sake, where isolates of S. cerevisiae, previously known as Saccharomyces saké, is used (105). For distilled alcohols, the vast majority of modern distilleries use starter cultures of S. cerevisiae; exceptions are Schizosaccharomyces pombe, used for production of specific spirits, and lactose-fermenting yeasts, used in the production of neutral spirit from whey (106).
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