EFFECT OF WHOLE BUNCH VINIFICATION ON THE ABUNDANCE OF A SWEETENING COMPOUND

Abstract

In classic red wine-making process, grapes are usually destemmed between harvest and the filling of the vat. However, some winemakers choose to let all or a part of the stems in contact with the juice during vatting, this is called whole bunch vinification. For instance, this practice is traditionally used in some French wine regions, notably in Burgundy, Beaujolais and the Rhone Valley. The choice to keep this part of the grape is likely to affect the sensory properties of wine, as its gustatory perception1,2. Previous studies have focused on the chemical composition of stems and have shown that astilbin, a sweet molecule, is a one of the major phenolic compounds3,4. The aim of this study is to investigate the effect of whole bunch vinification on the concentration of astilbin in wine.

Several experiments have been carried out in various French wine regions, in Burgundy, Beaujolais and Bordeaux over three vintages allowing to compare different grape varieties namely Pinot Noir, Gamay and Merlot. The addition of stems is carried out while filling the vats, according to different proportions ranging from 15 to 50 % of the total volume of introduced grape. For each experiment, the modality with addition of stems is compared with a vat of destemmed grapes coming from the same plot. Samples were taken throughout the wine-making process to be analyzed by liquid chromatography coupled with high resolution mass spectrometry (UHPLC-Exactive, Orbitrap analyzer).

The comparison of astilbin content in the two modalities showed that the addition of stems during vatting significantly increased astilbin concentration. Furthermore, this increase varies according to the grape variety. Indeed, the ratio between the astilbin concentration of wines from the two modalities is higher in Merlot than in Pinot Noir and Gamay. The localization of astilbin in the different components of Merlot and Pinot Noir bunch was also investigated in order to better understand this difference.

This study provides new insights on the contribution of stems to the concentration of a sweet compound, astilbin. Besides, these results bring new tools to better understand the practice of whole bunch vinification from a chemical perspective.