Gamay And Gamaret Winemaking Processes Using Stems: Impact On The Wine Aromatic Composition.

Stems may bring various benefits to the wine such as alcoholic reduction, color protection or improvement of the tannic intensity. Not much used on Swiss grape varieties, the aim of this study was to identify the relevance of using this type of winemaking in the case of Gamay and Gamaret red grape varieties. In this presentation, focus will be done on the aromatic compounds brought to the wine from the stems.
Gamay and Gamaret wines were made according to five modalities: fully destemmed used as control, 20% and 40% either whole grapes or stems added to the rest of the destemmed harvest. The influence of the stems on the wine chemical properties was measured using
different classical FTIR and colorimetric methods (alcohol, acidity, pH, SO2 …). Volatile composition of wine was analysed by gas chromatography coupled to  a mass spectrometer (GC-MS). The analysis of compounds with an aroma impact by olfactometry completes these analyses. Sensory analysis were also performed in order to measure the impact on the wines.
To understand the influence of stems, stem extracts were obtained from the same harvest batch using a maceration under simulated alcoholic fermentation protocol. These extracts were also analysed by GC-MS-olfactometry. The analytical results show differences between the aromatic profiles of the Gamay and Gamaret stems alcoholic extracts. The presence of terpene alcohol with floral notes such as linalool, geraniol or α-terpineol are particularly present in the alcoholic extracts of Gamaret stems. Gamay stems extracts have a more complex volatile compounds profile with esters and alcohols (fruity notes) present in greater quantities.
The presence of stems at different percentages and form during winemaking also influences the general aromatic profile of the different modalities.
This study allows us to acquire knowledge about winemaking processes performed using non-destemmed grapes and their impact on the wine characteristics. 

Authors: Blackford Marie1,2, Comby Montaine1,2, Imhof Janina2,Roesle-Fuchs Julie2, Dienes-Nagy Ágnes1, Fuchsmann Pascal1, Lorenzini Fabrice1, Bourdin Gilles1 and Bach Benoit2

1AGROSCOPE
2Changins, Viticulture and oenology, HES-SO University of Applied Sciences and Arts Western Switzerland

*corresponding author: marie.blackford@agroscope.admin.ch

Keywords: Stem, whole cluster, winemaking, aromatic compounds

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