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RESEARCH PRODUCT

Adsorption and diffusion study, in gazeous phase, of wine active molecules in cork

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During wine ageing, oxidation reactions occur and can lead to wine sensory defaults. The main factors involved in this phenomenon are oxygen and gas barrier properties of stoppers. During the last ten years, some studies investigated oxygen transfer during winemaking and wine storage. However, only few of them deal with the interactions between molecules and sealing materials. The material studied in this work is raw cork, without any treatment, neither washed nor surface treated (with paraffin or silicone). This Phd work focuses on mass transfer of some wine active molecules, in gas phase, through the cork. The selected molecules are water, ethanol, sulphur dioxide and oxygen. An adsorption thermodynamic study is performed on single compounds and on binary mixture, by means of thermogravimetric and differential calorimetry analysis. Three main results emerge from this study. First we show that the adsorption mechanism of single compounds varies according to the adsorbate. Water molecules are physisorbed whereas ethanol and sulphur dioxide are both physisorbed and chemisorbed. Moreover, a swelling phenomenon is highly suspected for water and ethanol. Then, adsorption of binary mixture of water and sulphur dioxide reveals that the equilibrium is shift in favour of water. Therefore, the small quantity of sulphur dioxide adsorbed cannot explain its concentration decrease during wine storage. Finally, a detailed study of oxygen transfer through cork, carried out by a manometric method developed in our laboratory, combines experimental and modeling approaches. For the first time, a diffusion coefficient of oxygen through cork is given by taking into account the cork material heterogeneity.