Alcohol wine quality

In another very recent paper (Son et al., 2009b), the fermentative performances of yeast strains used for grape must fermentation were monitored by NMR and multivariate statistical methods. Characterization of the properties of wine yeasts is important because they affect wine quality. In this paper, the changes of metabolites in must during alcoholic... 

In Table 5.2 and Figure 5.5, data for a quantification comparison between the two techniques referred to some compounds important for the wine quality such as esters, alcohols and fatty acids relative to analysis of different wines, are reported. Figure 5.5 shows the straight line regressions between the concentrations measured after XAD-2 extraction and the ratios of GC-FID area of each compound to that of the internal standard applying the Kaltron method. 

Microbial interactions that occur in wine may be beneficial or detrimental to wine quality depending on the species involved. Examples of detrimental interactions are the inhibition of S. cerevisiae by Lactobacillus species and the inhibition of O. oeni by S. cerevisiae when MLF is desired. However, the inhibition of O. oeni may also be beneficial to wine quality if MLF is undesirable. Additional beneficial interactions include the stimulation of LAB growth due to yeast lysis and the inhibition of Pediococcus species by O. oeni. A better understanding of the complex interactions between LAB and S. cerevisiae will lead to the selection of compatible yeast and bacterial strains for the induction of alcoholic and malolactic fermentations. 

Ce compounds. All Rojal wines displayed higher concentration of Cn alcohols, principally 1-hexanol. C6 compounds, which supvply "vegetal" and "herbaceous" nuances to the wine, usually have a negative effect on wine quality when their concentration is above their odor threshold values (Ferreira et al., 1995). However, 1-hexanol and (Z)-3-hexen-l-ol were found... 

Another technique to extract color from red grape cultivars is thermovinification. Here, a portion of the must is heated to 50°G/122°F to 60°C/ 140°F and mixed with the skins for a short period of time (Boulton et al., 1996). The must is then pressed prior to inducing alcoholic fermentation. In an interesting study by Malletroit et al. (1991), the effect of pasteurization on the microbiological and sensory quality of white grape juice and wines was investigated. The authors concluded that a pasteurization treatment equivalent to that used in the brewing industry is sufficient to reduce non-Saccharomyces populations prior to alcoholic fermentation without detrimental effects on wine quality. 

In conclusion, this feimentor design avoids alcohol loss by evaporation. Press wine quality is greatly increased, while the laborious work of cap punching is eliminated. This kind of tank has also been empirically observed to facilitate malolactic fermentation. 

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. 

Lactic add is also formed, reaching 22 mEq/1. This production cannot be explained by alcoholic (7 mEq/1) and malolactic (6 mEq/1) fermentation alone. Malolactic fermentation is nevertheless complete and contributes to wine quality. 

III. "Generous" or Fortified Wines, 17—21% alcohol. Thek nature and keeping qualities depend heavily on the addition of distilled wine spkits. 

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