Effects of Inactive Yeast Biostimulants on Mechanical and Color Attributes of Wine Grape Cultivars

Background: Biostimulants naturally improve plant growth, stress tolerance, nutrient use efficiency and activate defenses by increasing protective metabolites (phenols, anthocya-nins) in grapes. In viticulture, especially when using inactive yeasts, they modulate genet-ic expression, improve skin resistance, color and aroma profile of wine grapes in line with sustainable practices. Methods: Two wine grape cultivars, Merlot and Cabernet Sauvi-gnon, were sprayed with the inactive yeast Saccharomyces cerevisiae in a single treatment in pre-veraison or in a double treatment in pre-veraison and veraison. Berry weight, must, total polyphenols, anthocyanins, mechanical and colorimetric properties were measured on fresh grapes. Results: Two-way ANOVA revealed that TA, pH and TPC were not af-fected, while mean berry weight and anthocyanin content varied by cultivar, treatment and interaction; TSS differed only by cultivar. Inactive yeasts reduced weight in the single treatment thesis but stabilised it in the double treatment one; anthocyanins decreased in Cabernet Sauvignon but increased in Merlot. Mechanical and colorimetric analyses showed cultivar-dependent responses, with significant improvements in elasticity, skin thickness and hue of berries, especially in Merlot when the treatment was applied twice. Conclusions: Inactive yeasts showed an effect on the weight of the berries, the anthocya-nins, the mechanics and the color: Merlot significantly improved skin thickness, elasticity and hue. while Cabernet remained less reactive to treatments.