Impact of grape maturity on esters content and sensory characters in wines fermented with yeast strains of different genetic backgrounds

Abstract

Grapes composition is a factor well known to affect wines composition and sensory expression. The goal of this study was to evaluate how grapes composition modifications linked to maturity level could affect wines aromatic expression and esters composition. An experimental design has been developed from grapes of Vitis vinifera cv Merlot. On each vine plot, grapes have been harvested at two maturity levels and then have been fermented under standardized condition with two yeast strains : a commercial one and another obtained by deletion of the four main esterases of the previous one. Fermentation performed with the esterases deletes strain led to wines with main ester levels generally lower by a factor 5 to 10 in comparison with the original strain.

Merlot wines from the highest maturity level and fermented with the commercial strain shown lower concentrations for fatty acids ethyl esters and higher alcohol acetates but higher concentrations for some substituted ethyl esters like ethyl leucate. When fermentations were performed with an esterases deleted strain, all esters contents remained the same.

Sensory analysis confirmed these results. For the wines fermented with the commercial strain, when the maturity increased, wine fruity aromatic expression decreased (particularly its global intensity and the fresh, redberry- and fermentative fruits character) whereas when the fermentation was performed by the deleted strain wines fruity characteristics were the same.

Aromatic reconstitution performed, on one hand, to erase the consequences of maturity differences and, on the other hand, to erase the consequences of the strain performing alcoholic fermentation on esters contents showed that esters were not, alone, responsible for the difference of sensory characteristics for wines from very ripe grapes (particularly for the jammy fruit notes) but that their presence was essential for the perception of this difference. 

Our results highlight once again the role of esters in the overall wine fruity aromatic expression and underline their indirect importance in the perception of some varietal characteristics through perceptive interaction phenomena.