Alcoholic fermentation. From must to wine.
Written by torosidiswine
The conversion of must into wine by yeasts, in the absence of air (oxygen) is the well-known alcoholic fermentation. In essence, a high concentration of sugars (glucose and fructose) is converted through a series of metabolic stages (glycolysis, alcoholic fermentation) into carbon dioxide and ethanol, along with a variety of by-products formed in relatively low concentrations.
Alcoholic fermentation is mainly carried out by yeasts of the genus Saccharomyces and especially by the strains of cerevisiae (Fleet and Heard 1993, Henschke 1997b, Lambrechts and Pretorius 2000). These yeasts are either found naturally in the bark of the rails, in the harvesting and processing equipment at the winery, or added as a starting culture.
As the initial yeast population (1-5 x 106 cells/mL) grafted onto the must is usually not sufficient to complete fermentation, they must be multiplied so that an adequate fermentation rate can be achieved.
The growth of yeasts, however, depends on the availability of appropriate sources of nutrients in addition to sugars and especially nitrogen (Henschke and Jiranek 1993, Albers et al. 1998, Magasanik and Kaiser 2002). Nitrogen is an important trigger for alcoholic fermentation, as by reducing it, the rate of fermentation can actually decrease, even stop (Lagunas 1982, Salmon 1989, Manginot et al. 1997).
Grapes usually provide essential nutrients for yeasts, and represent the main source of endogenous nitrogen, unless supplementation is added by the winemaker. The decision to add nitrogen supplement to the must should be made based on the measurement of digestibility by the yeasts before fermentation, the winemaking conditions (e.g., yeast strain, temperature, aeration) and the type of wine (Henschke 1997a).
Πηγή : Bell S-J and P.A. Henschke , 2005. Implications of nitrogen nutrition for grapes , fermentation and wine. Australian Journal of Grape and Wine Research 11 , 242-295.
The conversion of must into wine by yeasts, in the absence of air (oxygen) is the well-known alcoholic fermentation. In essence, a high concentration of sugars (glucose and fructose) is converted through a series of metabolic stages (glycolysis, alcoholic fermentation) into carbon dioxide and ethanol, along with a variety of by-products formed in relatively low concentrations.
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