Effect of pre-fermentative addition of oenological tannins on the volatile composition and colour characteristics of white wines

Abstract This study investigates the effect of pre-fermentative addition of oenological tannins on basic physicochemical parameters, total polyphenols index (TPI), antioxidant activity (DPPH method), colour traits, and volatile organic compounds (VOCs) of white wines made from ‘Vermentino’ or ‘Erbaluce’ grapes (Vitis vinifera). Six oenological tannins were used, including hydrolysable (ellagitannins, gallotannins) and condensed tannins (derived from grape skins, grape seeds, quebracho, and acacia), at a dose allowing a similar increase in the TPI value. Nano-vinifications (300 mL) under controlled conditions were evaluated at three alcoholic fermentation stages (80 g/L, 20 g/L, < 2 g/L of reducing sugars; fermentation lasting 18 days). Tannins addition did not significantly influence the basic physicochemical parameters and fermentation kinetics, but it increased TPI and antioxidant activity as expected. In the final wine, the highest TPI value was observed for grape seed tannin, while the grape skin and grape seed tannins exhibited the greatest DPPH values in Vermentino and Erbaluce wines. Colour characteristics determined according to CIELab system [1] showed that the acacia tannin trial resulted in the greater colorimetric difference (∆E*) with respect to non-added samples in the pre-fermentative stage (lower L* and higher b* colour coordinates). In Vermentino and Erbaluce wines, these colour differences diminished in most of cases, with gallotannin and grape skin tannin having the least impact. Free VOCs were determined by HS-SPME-GC-MS at the three stages of fermentation [2] and possible changes in volatility were evaluated by simulating the fermentation conditions [3]. Regarding Vermentino, the wines obtained using quebracho tannin showed the highest concentration of all VOCs classes, particularly ethyl esters and acids, increasing total VOCs concentration by up to 28% compared to the control sample. Esters and acids also increased in wines resulting from acacia and grape skin tannin trials but the concentration of terpenes and norisoprenoids was negatively affected. Moreover, grape seed tannin better preserved higher alcohols (mainly 2-phenylethanol), acids, and norisoprenoids. Regarding Erbaluce, the effects were less pronounced. Ellagitannin, quebracho, and grape seed tannins increased the concentration of esters by around 5% whereas tannins from exotic woods decreased that of benzenoids by 10%. Individual VOCs results showed that oenological tannins can significantly improve wine aroma complexity but a varietal effect was observed.