Extraction of oak volatiles and ellagitannins compounds and sensory profile of wine aged with French winewoods. Implication of chemical composition on the final wine quality

The evolution of volatile and non volatile compounds extracted from winewoods while being macerated for 12 months in Merlot wines was studied. Seven types of winewoods subjected to different toasting methods were used. Sensory analysis concerning vanilla, spicy, overall woody, astringency, bitterness and sweetness was conducted in parallel. Different rates of extraction have been observed, depending mainly on the origin of the compounds in the wood (toasting or present in natural wood) as well as on the watering process during toasting. The above differences are reflected by perceived sensory differences. Astringency and bitterness are related significantly to ellagitannin levels (R = 0.828, p = 0.001 for astringency and R = 0.607, p = 0.005 for bitterness). Judges perceived sweeter the wines that presented more lactones and vanillin levels. Spicy and vanilla descriptors are related to eugenol and vanillin as well as to other odorous chemicals. This study provides some insight into the implication of nonvolatile composition on astringency sensation as well as on bitterness and sweetness perception. INTRODUCTION Oak barrels have long been used in fine wine making, initially for easy product handling during production, storage and transport. Oak wood positive effects on wine development became appreciated, namely the ceding of pleasant aromas, and the regulation of red wine color. During aging in oak barrels, wines composition change because of the addition of phenolic compounds and other molecules extracted from the wood. Such compounds include lignins, hydrolysable and condensed tannins, gallic acid, ellagic acid, aromatic carboxylic acids, and various aldehydes. Ellagitannins (hydrolysable tannins) are among these substances. In oak heartwood they may represent 10% of the dry weight and are responsible for the high durability of this wood (Scalbert, et al., 1988). Oak also contains a high level of volatile compounds that have a great impact on woodmatured wines aroma. The main volatile compounds susceptible to migration from oak wood to wine are the cis and trans isomers of β-methyl-γoctalactone, furfural and its derived compounds, phenolic aldehydes such as vanillin and syringaldehyde, and volatile phenols such as eugenol, guaiacol, and ethyland vinylphenols. Their extraction of oak barrels depends mainly on the quantity of compounds that are potentially extractible on the contact time between wine and oak wood and on the wine composition. At present, alternatives to the oak barrel are being looked at to carry out the wine-ageing process. This practice recently was approved and legislated by the European Community (CE 2165/2005 and CE 1507/2006). Different shapes of oak wood pieces are used: chips, cubes or beans, powder, shavings or granulates, dominoes, and blocks or segments. Factors such as piece size, amount of added wood and contact time between wood and wine affect both sensory and chemical wine characteristics (Frangipane, et al., 2007) especially their wood-related volatile composition. Up to now, it does not seem very logical to establish an ageing period in barrels or with wood pieces through legislation. Hence, it would be important to know more about the influence of the wine composition in the process of the extraction of oak wood compounds. It is likely that a study of wine volatile and non volatile composition along with a tasting assessment would