Ethanol winemakers

The sugars in fruits such as grapes are feimented by yeasts to produce wines. In winemaking, lactic acid bacteria convert malic acid into lactic acid in malolactic fermentation in fruits with high acidity. Acetobacter and Gluconobacter oxidise ethanol in wine to acetic acid (vinegar). 

Total phenols extracted into red wines by skins and seeds usually increase with an increase in contact time, temperature, ethanol, SO2, and maceration. These are the factors at the winemaker s disposal that have a large effect upon the style of wine he wishes to produce. 

After the process is completed to the winemaker s satisfaction, the wine is fortified to 17-19 percent ethanol, is clarified, and the yeasts are filtered out. The addition of ethanol seems to intensify the flor aroma. 

The fluidity of the plasmatic membrane is considerably affected by temperature (Rodriguez et al. 2007) and ethanol concentration (Jones and Greenfield 1987). Therefore, during alcoholic fervaeniaiionSaccharomyces cerevisiae must adapt the fluidity of the membrane to the changing environmental conditions. It should be emphasized that the temperature of fermentation and aeration depend on the type of winemaking. Usually, white wines are made at low temperatures (14-18 °C) and without aeration to conserve aromas whereas red wines are fermented at relatively high temperatures (28-30 °C) and are aerated in order to enhance colour extraction. 

Patynowski et al. (2002) showed that yeasts produce an unidentified inhibitory factor (maybe a toxic metabolite) that could be responsible for the inhibition of bacterial growth. These results could explain the antagonism between yeasts and malolactic bacteria, since yeasts are known to produce compounds during alcoholic fermentation such as ethanol, SO2, medium-chain fatty acids and antibacterial proteins/peptides (Weeks et al. 1969 De Oliva et al. 2004 Comitini et al. 2005 Osborne and Edwards 2007). The nature and quantity of peptides and other molecules released by yeasts are different depending on winemaking techniques and the yeast strain. 

Finally, as Martini and Martini (5) note, the selective pressures at work in the winery environment may influence the survivability of the indigenous yeasts with respect to ethanol or sulfur dioxide tolerance it is not clear, however, how such environmental pressures would be selecting for desired flavor production. Certainly few winemakers completely sterilize their wineries and scorch their vineyards when they obtain a wine with less than optimal flavor attributes ... 

In many countries, alcoholic fermentation is induced by inoculation with a yeast starter culture of Saccharomyces selected for its desirable winemaking qualities (Kunkee, 1984 Kunkee and Bisson, 1993 Rainieri and Pretorius, 2000 Reed and Chen, 1978 Reed and Nagodawithana, 1988). Starter cultures of S. cerevisiae strains are generally used because of to their increased ethanol and sulfur dioxide resistance and production of desirable aromas and flavors (Boulton et al., 1996 Ebeler, 2001 Nykanen, 1986 Reed and Chen, 1978 Reed and Nagodawithana, 1988). 

Winemaking essentially involves fermentation of a must containing sugars and flavor elements to a solution of ethanol plus flavor elements still containing some residual sugar. 

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