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38 WINES&VINES April 2017 BARRELS PRACTICAL WINERY & VINEYARD O ak aging is a crucial step in winemaking, during which the organoleptic properties of wine are modified. Various parameters affect the chemical com- position of oak, and botanical origin previously has been shown to be a de- terminant factor. Sweet natural triterpenes arising from cooperage oak and the effect of oak species (Quercus petraea and Quercus robur) on four recently discovered taste-active triterpenes (three sweet and one bitter) were analyzed. The results showed that sessile oak or Quercus petraea (27 samples) was richer in sweet triterpenes and poorer in the bitter one than pedunculate oak or Quercus robur (19 samples), with high inter-individual variations within species. A triterpenoid index was calculated to reveal the triterpenoid composition of oak. This index appeared as a promising tool for the unambiguous discrimination of oak species and could offer new insights concerning oak selection by coopers and the monitoring of élevage by winemakers. The quality of a wine relies both on the value of the harvested grapes and control of its winemaking pro- cess. For many wines, a maturation period involves contact between wine and oak wood, wine bouquet and taste being profoundly modified during this step. These modifications can be due to the moderate oxida- tion of wine compounds during élevage or to the release of molecules from wood. 1 The research in this field has led to identification of the key volatile compounds coming from oak: vanil- lin, β-methyl-γ-octalactone (oak-lactone), eugenol and 2-furanmethanethiol. 2,3 To a large extent, these vola- tiles explain the vanilla, coconut, spicy and roast coffee aromas typical of oaked wines. Moreover, oak releases non-volatile compounds likely to modify the taste of wine. In practice, winemak- ers observe the modification of tannin perception of wine (structure and dryness) and bitterness as well as perceptions described as volume or sweetness. Sweet Triterpenoids in Oak for Cooperage Uncovering the difference between sessile and pedunculate oak By Axel Marchal, Pierre Waffo-Teguo, Andrei Prida and Denis Dubourdieu SEGUIN MOREAU