Wood from barrique: release of phenolic compounds and permeability to oxygen
Abstract
Chemical and sensory changes occurring in red wine during ageing in oak barrique are due to the slow and gradual entrance of oxygen along with a release of ellagic tannin from the wood. Though oxygen can enter the cask through the bunghole, it is not clear the role of permeation through the wood staves as well as the amount of oxygen entering by permeation. The distribution of the released ellagic tannins in the wine ageing is also unknown. The oxygen passing through the bunghole may have a different wine ageing effect compared to the oxygen permeating through the wooden staves owing to the uneven ellagic tannin concentration throughout the wine. This tannin acts as essential oxidation mediator since it prevents the straight oxidation of flavan-3-ol units and anthocyanins in wine ageing. On these bases, the release of phenols was monitored in a model solution where oak wood was soaked. The solution was stored in the dark at 15°C for two weeks and then it was recovered. Samples were drawn at different distance and depth from the wood. The release of phenols was evaluated for further two weeks to mimic the use of the barrique. Moreover, the permeability of oak wood to oxygen was investigated in either dry or wet oak wood. Results showed that higher concentration of tannin occurred near to the wood (vertically placed staves) and close to the bottom of the container, whereas higher concentration of phenols was still revealed following to the second soaking of the staves in the deepest layer of the solution but farther away from the wood. According to the experimental data, the release of tannins followed a gradient towards the bottom of the container probably due to the higher density of the solution. The oxygen transmission rate through dry oak wood approached 5 g m-2 day-1 and it decreased 5-6 times when wet wood was considered. The oxygen inside the barrique could be estimated to about 15 g L-1 year-1 considering the barrique full of wine. Such values appeared by far higher than the values suggested in the updated literature and showed the essential role exerted by the wood tannin in protecting the phenols of red wine from oxidation.
Issue: Macrowine 2016
Type: Poster
Authors
*DeFENS-Università degli Studi di Milano