Towards a model of grape tannin extraction under wine-like conditions: the role of suspended mesocarp material and anthocyanin concentration

Background and Aims: The study aimed to determine how fresh grape mesocarp modifies the extraction and composition of tannin under wine-like conditions. A further aim was to observe whether addition of anthocyanin during extraction exerted an effect on the concentration of recovered tannin. Methods and Results: Fresh red grape berries were dissected into skin, mesocarp and seed. Different combinations of the berry components were extracted in model wine or fermented. Initial results indicated that mesocarp material bound seed tannin more selectively than skin tannin. Further experiments pointed towards a more complex system, whereby adsorption of tannin by mesocarp facilitated ongoing extraction of tannin from the skins. The effect exerted by mesocarp was potentially to increase the concentration gradient between skins and the liquid medium by the continuous removal of tannin. Under these conditions, both skin and seed tannin could be removed from extracts or wines by suspended mesocarp material. White grape skins or mesocarp were also extracted with the addition of a variable concentration of purified anthocyanin and found to facilitate the extraction of otherwise non-extractable tannin. This effect was observed to be greater for grape mesocarp than for white grape skins. Conclusions: The concentration and composition of tannin were shown to be modified by the presence of mesocarp material. A role for anthocyanin in enhancing the extraction of tannin was confirmed. Significance of the Study: The results show that multiple factors interact to influence tannin extraction and retention from grapes.