Control of Redox Potential during Wine Fermentations at Research, Pilot, and Commercial Scales
James Nelson,* Robert Coleman, Leticia
Chacon-Rodriguez, Ron Runnebaum, Roger Boulton, and Andre
Knoesen
*University of California, Davis, 1 Shields Ave, Davis, CA, 95616
(jjnel@ucdavis.edu)
Redox potential (oxidation-reduction potential or ORP) is an electrochemical measurement of the active oxidation and reduction components in a chemical system. The extracellular ORP during microbial fermentation determines whether certain redox reactions take place, affects the intracellular redox potential of microbes and therefore the whole metabolic process, and is easily measured with an ORP probe in the fermentation media. During wine fermentation, controlling ORP above its natural levels is expected to affect yeast metabolism and the formation of certain products, such as mitigate the formation of H2S from elemental sulfur. While control of ORP during wine fermentation has previously been demonstrated at a research volume (100 L), the purpose of this project is to demonstrate that control of ORP can be scaled to large volumes common in commercial winemaking. There are no known examples of wine fermentations with controlled ORP at commercial volumes. Typically, commercial fermentations lack mixing and at larger volumes, the measurement of any process parameter such as density, temperature, or ORP will be affected by stratification. We measured and controlled ORP in 100, 1500, and 10,000 L Cabernet Sauvignon fermentations under identical fermentation conditions. A controller was developed to add air into the juice if the ORP dropped below the setpoint of 160 mV (-40 mV Ag/AgCl), while non-aerated fermentations fell below 120 mV (-80 mV Ag/ AgCl). The system properties of redox potential during wine fermentation were also studied. Across the three volumes (100, 1500, and 10,000 L), we will demonstrate the redox potential effect of a typical red winemaking extraction method coupled with venturi introduced air versus direct injection of compressed air into the fermentation. While a simple on-off controller was used in this work, this study of the system properties may motivate more complex control systems with improved performance.
Funding Support: T.J. Rodgers Fellowship in Electrical and Computer Engineering, Treasury Wine Estates, Stephen Sinclair Scott Endowment in Viticulture and Enology
