| During the period of maturation in wood, two main phenomena occur:
Oxidation of substances present in the wine linked to the penetration of oxygen through the wood
Wood enables an exchange between wine and the atmosphere. Oxygen which enters the wine combines with certain phenolic substances contained in the wine, and also with ellagitannins (tannins from oak), which are soluble in wine. Ellagitannins serve to transport oxygen between the air and the wine, whilst protecting the substances contained in the wine from oxidation.
The barrel is a tool used for natural oxidation which enables the phenolic structure of red wines to be improved. It prevents white wines forming unpleasant reduction aromas that come from the metabolism of yeasts and this is all the more true when wine is stored in new barrels, richer in tannins which are catalysers of oxidation.
The diffusion of compounds released by oak wood
Compounds that come from oak wood influence the development of aromas and flavours of wines matured in wood.
Two main aspects of their diffusion have been identified.
1. Direct organoleptic changes linked to organoleptic characteristics released by wood
Fragrance characteristics of “woody” wines are linked to corresponding molecules released by wood and present in concentrations higher than their levels of perception: Vanillin = vanilla, Eugenol = spices, clove, Whisky-lactone = young wood, coconut, Furanic substances = almond, grilled hazelnut, Guaicol, 4-Methyl-guaicol = smoky aromas.
Other molecules present in quantities lower than their levels of perception are the cause of a subtle “woody” character, much sought-after in quality wines. These compounds also play the role of increasing certain aromas in wine. For example, Maltol strengthens the “sweetness” of a wine.
The interaction of compounds released by wood with the natural micro-flora of a wine (yeasts and bacteria) can quite significantly modify the perception of the “woody” aroma. In the case of alcoholic fermentation in barrels, we observe a reduction of the impact of wood: this subtler hint, perceived as delicate and elegant, is due to a reduction phenomenon characteristic of wine-making in wood.
2. Indirect organoleptic changes, linked
to transformations of compounds in wood that can be released in wine and their interaction with substances contained in wine.
The indirect effects are mainly linked to the presence of ellagitannins:
• Their presence begins a chain of successive chemical reactions which contribute to stabilising colour in red wines.
• They speed up the condensation of proantocyanidines (tannins in wine), which reduce astringency.
• They contribute to the formation of links between polysaccharides and proteins which are released when lees are regularly “stirred up” during the maturation period of fine white wines.
All these various mechanisms contribute to improving the structure and bouquet of fine wines, characterised by the delicacy of their aromas, the length of their flavours on the palate and their longevity.
Seguin Moreau
www.seguin-moreau.fr
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