Impact of Seaweed and Yeast-Based Biostimulants on the Oenological Quality of Merlot Wines in Warm Climates

Climate change-induced metabolic decoupling in grapevines compromises wine quality in warm regions, making the use of foliar biostimulants a promising mitigation strategy. This study evaluates the impact of seaweed extract with silicon (SWE-Si) and yeast/bacteria extract (YBE) on Merlot grapes under warm climate and restrictive water conditions. The resulting wines were evaluated to check the effects on grapes. Following standardized micro-vinifications, wines were characterized by their physicochemical, phenolic, and volatile profiles, alongside discriminative sensory triangle tests. Both biostimulant treatments accelerated ripening, leading to increased alcoholic levels compared to the Control. SWE-Si significantly enhanced phenolic accumulation, specifically increasing total anthocyanins by 89% and tannins by 70%, while YBE-treated wines exhibited a substantial increase in medium-chain ethyl esters, particularly ethyl decanoate. Hierarchical Cluster Analysis confirmed distinct aromatic fingerprints for each treatment. Sensory panels successfully discriminated all treated wines in visual, olfactory, and gustatory phases. These findings demonstrate that foliar biostimulation effectively modulates Merlot chemical and organoleptic profiles, with SWE-Si favoring color and structure and YBE enhancing fruity aromatic profiles. Consequently, strategic biostimulant application provides a practical tool for optimizing wine quality in climate-threatened viticultural regions.