Impact of Grape Maturity on Ester Composition and Sensory Properties of Merlot and Tempranillo Wines

The goal of this study was to evaluate how grape composition modifications linked to maturity level could affect the wine ester composition and aromatic expression. An experimental design has been developed from grapes of Vitis vinifera cv Merlot and cv Tempranillo. On each vine plot, grapes have been harvested at two maturity levels and have been fermented using a commercial yeast strain under standardized conditions, specifically after having the sugar and nitrogen concentrations adjusted to the same target values. Tempranillo wine ester content was not impacted by the maturity level, whereas Merlot wines from the highest maturity level showed lower concentrations for fatty acid ethyl esters and higher alcohol acetates but higher concentrations for substituted ethyl esters. Sensory analysis corroborated these analytical results: when Merlot maturity increased, wine fruity aromatic expression decreased (particularly its global intensity and the fresh, red-berry, and fermentative fruit characters). In addition, aromatic reconstitution experiments showed that esters were not, alone, responsible for the sensory differences linked to grapes' maturity. Globally, our results highlight the role of esters in the overall wine fruity aromatic expression associated to Merlot ripeness and show that their levels are impacted by other parameters than the grape content in sugars and amino acids, well known as being their precursors.