Abstract

Oxygen management is critical to ensure the appropriate development of yeast and avoid its detrimental effects on sensory quality of wine. Oxygen additions during alcoholic fermentation are typically carried out through pump-over operations, which contributions have not been appropriately quantified. In this work, we designed a set of experiments with different pump-over modes (closed, open, and with Venturi) to evaluate oxygen dissolution and consumption during industrial-scale fermentations. Closed pump-overs incorporate negligible amounts of oxygen, while open pump-overs with Venturi incorporate the highest, i.e., 3 mg/L (approximately twice more oxygen than the conventional open pump-overs). A highly heterogeneous vertical distribution of dissolved oxygen was also found, with approx. 80 % of the total concentrated at the top of the tanks. When analyzing oxygen dissolution during the maceration, initial low oxygen levels were encountered in spite of the high free SO2 concentrations (an inhibitor of enzymatic oxidation). We speculate that the latter is due to the high initial CO2 content, which prevents oxygen dissolution during the initial period. In the case of the fermentation stage, the observed low oxygen concentrations are mainly due to elevated yeast activity. We also followed oxygen dissolution kinetics during fermentation by estimating the oxygen dissolution rate and a global consumption constant for different fermentation stages. Our results confirmed the negative impact of CO2 on oxygen dissolution and the elevated yeast biological activity of the tumultuous fermentation, as the main causes for the observed low dissolved oxygen levels. Overall, the present work will help improve the management of oxygen during fermentation and winemaking.