UC Davis

Every year the wine industry faces significant financial losses because of stuck fermentations and the presence of reductive faults in finished wines. Currently, most wineries rely on temperature and °Brix metrics to monitor the progress of a fermentation. However, these parameters do not reflect the chemical and metabolic status of a fermentation in real time. Redox potential, or Oxidation Reduction Potential (ORP), is an emerging process parameter in the wine industry. It offers a valuable real-time indicator of the redox status of a fermentation, which correlates with yeast metabolism and dynamics, fermentation kinetics, and hydrogen sulfide production. Controlling redox via aeration has the potential to facilitate more robust fermentations, help avoid costs associated with problematic fermentations and could be used to make decisions to prevent the formation of unwanted compounds associated with reductive fermentation conditions. The goal of this study was to gain a better understanding of how oxygen introduction, at various times and amounts during fermentation, affects redox status and how this is linked to overall fermentation outcomes. Using juice concentrate as a consistent fermentation medium, the impact of oxygenation on redox potential and fermentation kinetics was investigated at lab scale. This work set out to evaluate when the introduction of air during fermentation is required to see improved fermentation performance. Redox, Brix and cell density data was collected in all trials and compared against un-aerated ferments and across those subject to different oxygenation time and redox set point regiments. Experimental results demonstrated that aerated ferments with higher redox status have faster fermentation kinetics and reach overall greater cell densities than those that were un-aerated. In addition, the timing of aeration was found to be important for this effect.