Climate Change Effect on Polyphenols of Grignolino Grapes (Vitis vinifera L.) in Hilly Environment

Climate change is modifying ecoclimatic conditions, including temperature, solar radiation, and water availability, with significant impacts on grapevine phenology, berry ripening, and the polyphenolic composition of grapes cultivated in temperate regions. The influence of different meteorological conditions during ripening on the polyphenolic composition of Grignolino grapes grown in a hilly environment was investigated. Grapes were collected, over three vintages, from three vineyards differing in their vine age and bunch microclimate due to having different vineyard aspects. We considered a comparable berry weight, moderate rainfall and cool conditions before veraison, followed by a warm and dry pre-harvest stage that enhanced the phenolic and especially the anthocyanin index in the grapes (e.g., 360 mg kg−1 in 2021 versus 260 mg kg−1 in 2020). Intense heat and dry conditions reduced the berry weight, leading to an increase in both flavonols and hydroxycinnamoyl tartaric acids, particularly in the younger, southwest-exposed vineyard. Older vines with a cooler aspect were the most resilient to different meteorological conditions, while young vines showed greater variability over the years. The phenolic composition was strongly influenced by the intensity and the timing of thermal stress, and eventually on limited water availability during ripening; it also depended on the vine age and the vineyard microclimate determined by the hillside aspect. This knowledge may support adaptive strategies to preserve grape quality under climate change.