Kaolin and Zeolite Reduce Drought Damage to Gewürztraminer and Influence Berry Composition, Must Quality, and Wine Aroma

Climate change is affecting Mediterranean viticulture regions due to frequent abiotic stress conditions such as drought and heat stress, which threaten grape and wine quality. Rock powders (Kaolin, Zeolite) have been identified as a possible adaptation strategy for abiotic and biotic stresses in grapevine. They influence leaf physiology and modify berry quality, thus wine characteristics, mainly by increasing organ reflectivity. This project assessed these rock powders’ influence on grapevine physiology (leaf gas-exchange, VPDleaf); berry sunburn incidence; and berry composition, must quality, and wine aroma. We investigated 3% kaolin and 3% zeolite in a 2-yr trial (2023 to 2024) on Gewürztraminer, an aromatic cultivar in northern Italy (Trentino Alto Adige), in an east-west oriented vineyard trained to a vertical shoot-positioned trellis system and Guyot pruned (two spurs, one fruiting cane, nine buds). Rock powders were applied to both canopy sides every 14 days and after rainfall in a randomized Latin-square design (252 vines, 3 rows, 12 plots each, n = 36), with bunch-zone leaf removal (No LR, LR BBCH75, LR BBCH81). Five and six applications were carried out in 2023 and 2024, respectively. Both kaolin and zeolite reduced leaf and berry temperature (p < 0.001, -6°C and -4°C, respectively), significantly limiting sunburn in berries (p < 0.05). Leaf physiology showed few differences between treatments, likely due to vintage-specific conditions, confirming that in rainy years, rock powders do not hinder ripening or physiological fitness, while preserving quality in hot/dry years. Some significant differences in aromatic compounds were found in musts and wine, however, wine tasting revealed no perceptible differences. Future studies will focus on the terpene biosynthesis pathway (MEP, MEV) under drought and heat stress to better clarify kaolin and zeolite effects on must and wine aroma.