Phenolic profiles of red straw wines: Impact of grape variety and ripeness on postharvest dehydration

Postharvest dehydration is applied as a winemaking strategy to increase sugar concentration and secondary metabolites in grapes, resulting in wines with peculiar compositional and sensory attributes. The process is influenced by temperature, relative humidity (RH), ventilation and duration, which determine water and weight loss (WL), and varies according to grape variety and ripeness [1]. The aim of this research was to evaluate the combined influence of ripeness level and grape variety on the phenolic profile of grape and resulting straw wines. ‘Corvina’, ‘Moscato di Scanzo’ and ‘Nebbiolo’ red grapes were harvested at three maturity levels (18, 21, 23 Brix) and subjected to dehydration (14–15 °C, 40–50% RH) until 20% WL. Total anthocyanins (ACNs) and flavonoids (TFs) were assessed in grape samples. After standardized micro scale winemaking, the resulting wines were characterized in terms of proanthocyanidin (PAC) profile. Mean degree of polymerization (mDP), conversion yield (CY) and galloylation (%G) were estimated. The investigated varieties showed distinct phenolic compound dynamics over the ripening and dehydration duration. Specifically, in terms of ACNs, negligible changes were observed for the increasing grape ripeness for all the varieties. In contrast, an increased concentration of FVs was found on wines processed from ‘Corvina’ harvested at 23 °Bx and ‘Moscato di Scanzo’ at 21 °Bx, while no change was shown for ‘Nebbiolo’. A distinct pattern was evidenced for wine PACs which composition substantially unchanged in Corvina and Moscato di Scanzo wines. A relevant decrease of catechin and epicatechin, both constitutive and terminal units, was observed for Nebbiolo wines from more ripen grapes. Overall, the increased ripeness of grapes led to a lower concentration of PACs detected in wines. Nonetheless, the variation of mDP was limited, and CY and %G remained constant despite greater maturity. This study contributes to a deeper understanding of varietal-specific responses to postharvest grape dehydration, focusing on red grape varieties traditionally employed in this technique.