Characterisation and extractability of tannins in Pinot noir grape skin, seed, and stem: Impact of leaf removal, clone, and rootstock

Abstract

This study examined the impact of leaf removal timing, rootstock, and clone selection on Pinot noir grape composition and subsequent impact on tannin extractability. Results showed that leaf removal increased anthocyanin levels in berries and tannins in stems and seeds, while also raising the mean degree of polymerisation (mDP) of skin tannins. Schwarzman rootstock had lower seed tannins but higher mDP in skin and seed tannins compared to own roots. UCD5 clone exhibited higher mDP in skin tannins than AM10/5 clones in acetone extraction. Tannin extractability was determined by the ratio of model wine-extracted tannins and acetone-extracted tannins. For the first time, this study reported that stems had the highest tannin extractability (64%-78%) compared to skins (37–52%) and seeds (26–34%). Compositional differences in grape tissues from different treatments had no impact on tannin extractability except for grape skins from two treatments. This suggests that tannin extractability is mainly influenced by grape ripeness which largely determines the composition of cell wall materials that can interact with tannins and thus influence tannin extractability. The differences in grape skin tannin extractability observed in this study between treatments were likely due to the significantly different galloylation (G%) levels in the extracted tannins.