After the barrels have been coopered and arrived at the winery, the process has only begun. They are filled with wine, and aging commences.
The wood begins to have a sensory influence on the wine, as the oak adds complexity, depth and dimension.
The barrel is a tool used for natural oxidation that 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, particularly when the wine is stored in new barrels, richer in tannins, which are catalyze oxidation.
Dr. Andrei Prida, SEGUIN MOREAU Research and Development Manager, and researchers have identified two main aspects of the diffusion of compounds released by oak wood:
- Direct organoleptic changes, linked to organoleptic characteristics released by wood
The dense yet porous grain allows for exchange of oxygen between the outside air and the wine. As the oxygen penetrates into the wood and then the wine, some of the wine’s substances begin to slowly oxidize.
Among these phenomena of exchange, there is the loss of wine through evaporation, which varies between one and nine percent, depending on the conditions of temperature and humidity in the cellar.
Monosccharoses, which cannot hydrolyze, mineral salts, and phenol aldehydes (vanillin, etc.) begin to release, as do phenol acids and ellagitannins.
- Indirect organoleptic changes, linked to transformations of compounds in wood that can be released in wine and their interaction with substances contained in wine.
Oxygen 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 indirect effects are mainly linked to the presence of ellagitannins. 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.
Their presence begins a chain of successive chemical reactions that contribute to stabilizing color in red wines, as well as speeding up the condensation of proantocyanidines (tannins in wine), which reduce astringency.