Effect of Wine Properties and Operating Mode upon Mass Transfer in Micro-Oxygenation

Abstract

All along wine-making and during its ageing, oxygen plays an important role for the evolution of the wine. Solubilization of oxygen into musts or wines occurs when gaseous oxygen is brought into contact with the liquid. In this work, the specific technique of wine microoxygenation is addressed through the evaluation of transfer capacity for oxygen solubilization. This was done considering the parameters likely to influence the saturation concentration of dissolved oxygen and the conventional volumetric mass transfer coefficient kLa, which quantifies the efficiency of the oxygen transfer. The study has shown that the sugar concentration in the must induces a viscosity enhancement which leads to a significant decrease of the kLa value. Surprisingly, it was also observed that a very low quantity of ethanol in the liquid phase (0.05 percent volume) strongly favours the oxygen transfer. Conversely, the presence of dissolved carbon dioxide in the wine, which desorbs and dilutes the oxygen in the micro-bubbles, dramatically decreases the transfer of oxygen. The presence of anti-oxidant compounds (SO2) or oxygen consumer compounds (polyphenols) was shown to have no effect upon the efficiency of oxygen transfer. Operating parameters such as gas flow rate or geometrical aspect of the tank have also been considered.