Cofermentation of Syrah with additions of 5, 10, and 20% (by weight) of the white variety Viognier was followed during winemaking and up to 580 days postpressing to assess the effect of Viognier additions on the chromatic and phenolic composition of the wines. Additions of 10 and 20% Viognier lowered most of the chromatic parameters. At day 580, no differences were observed for tannins and iron reactive phenolics among the wines. Analysis of anthocyanins and flavonols uncovered no differences between 100% Syrah and 5% Viognier wines but the 20% Viognier wines had lower concentrations of anthocyanins and flavonols, suggesting possible dilution of these phenolics. These results suggest that additions of Viognier at the rates studied here neither improve the phenolic composition nor enhance the color stability of the final wines.
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