THE EFFECT OF BENTONITE FINING ON THE VOLATILE AND NON-VOLATILE PROFILE OF ITALIAN WHITE WINES

Abstract

Marselan wines have an unusual high proportion of seed derived tannins from grapes having high proportions of skins, which are rich in tannins. But the causes behind this characteristic have not yet been identified. In vintage 2023 wines were made at experimental scale (9 kg by experimental unit) from Arinarnoa, Marselan and Tannat Vitis vinifera grape cultivars by traditional maceration, and by techniques aimed to increase the wine content in skin derived tannin: addition of extraction enzymes, addition at vatting of grape-skin enological tannins, or by extended maceration, known to increase the seed derived tannin contents of wines. Macerations were of 7 days, except in the extended macerations that were of 15 days. Additionally, samples of seeds and skins from each cultivar were separately macerated in a wine-like solution for 15 days. All treatments were made by triplicate. The contents of anthocyanins and tannins were analysed along macerations spectrophotometrically (tannins reactive to methyl cellulose, total anthocyanin) and using a HPLC-DAD system (pigments, flavan-3-ols). During the first 3 days of winemaking, Arinarnoa and Tannat musts had similar tannin contents that were much higher than those in Marselan musts. But at day 5, Arinarnoa had reached its maximum tannin content while in Tannat and Marselan it continued to increase until day 7. At this point, Marselan had as much tannin contents as Arinarnoa while Tannat had much higher concentrations. Along the post-fermetative macerations, Tannat tannin contents decreased while they continued to increase in Marselan. Thus, from day 13 to 15 of maceration Marselan and Tannat had similar tannin contents that were at devatting significantly higher than in Arinarnoa. The addition of skin tannins did not significantly increase the tannin concentrations of wines. Noteworthy, just in Marselan, the maceration enzymes significantly increased the anthocyanin and particularly the tannins concentrations of musts relative to the other treatments in a magnitude that increased with the maceration time. The macerations in wine-like solutions showed that the extraction of anthocyanins and particularly of skin tannins was very low in Marselan related to the observed in Arinarnoa and Tannat, while the seed tannins were extracted at similar rate in the three cultivars. This research proved that the high proportion of seed tannins in Marselan wines is due to a limited extraction of these compounds from the skins.