Winemaking, white aeration

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. 

Presence of medium chain fatty acids The presence of MCFA can decrease yeast viability and even stop alcoholic fermentation. This problem is more prevalent in white winemaking because fermentation is usually carried out at low temperatures and without any aeration. Yeast hulls have been very useful for avoiding this problem. Yeast hulls adsorb MCFA from the media and provide sterols and UFA to the yeasts. Yeast hulls can be used as preventives (20 g/hl) or as curatives (40-50 g/hl) of stuck and sluggish fermentations. 

The winemaking parameters that increase higher alcohol production by yeasts are well known high pH, elevated fermentation temperature, and aeration. In red winemaking, the extraction of pomace constituents and the concern for rapid and complete fermentations impose aeration and elevated temperatures, and in this case higher alcohol production by yeast cannot be limited. In white winemaking, a fermentation temperature between 20 and 22° C limits the formation of higher alcohols. 

The general mechanisms that link the nitrogen and oxygen needs of yeasts during the alcoholic fermentation process (Sections 2.4.2, 3.4.2 and 3.5.2), explain the advisability of the addition of ammonium salts and the necessity of aeration during dry white winemaking. 

The duration of dry white wine fermentation depends on several parameters juice extraction conditions sugar and assimilable nitrogen concentrations turbidity yeast strain aeration and fermentation temperature. The winemaker can adjust and control all of them. A slow or stuck fermentation is most often the result of carelessness and always affects wine quality. The alcoholic fermentation of a white wine should not exceed 12 days. Longer fermentations should not be songht after except in the case of exceptionally high sngar concentrations. 

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