Elucidating the Fundamental Mechanism of Phenolic Extraction in Red Wine Fermentations
Cristina Medina-Plaza, Jordan Beaver, Larry Lerno, Ravi Ponangi, Tom Blair, David Block, and Anita Oberholster*
*Department of Viticulture and Enology, University of California,
Davis, CA 95616 (email@example.com)
The general effects of processing and fermentation on wine composition, including phenolic composition, are well studied. The variable that most influences phenolics extraction is the temperature at which fermentation is performed. Elevated fermentation temperatures (approaching 30°C) produce finished wines that are more highly colored. Similarly, ethanol production affects phenolic extraction during red wine fermentation. Based on these findings, it is likely that the fundamental mechanisms and subsequent kinetics of phenolic extraction during red wine fermentation will be greatly affected by both factors. The effects of temperature, ethanol concentration, and anthocyanin concentration on adsorption and desorption processes of anthocyanin onto cell wall material were investigated. Independent variables included temperatures of 15 and 30°C, model wines with ethanol concentrations of 0 and 15%, and anthocyanin concentrations of 1 or 2 mg/mL. These experiments were conducted in small, benchtop solutions that mimic a single-berry fermentation environment. The desorption experiments were carried out immediately after completion of the adsorption experiments to minimize changes to the cell walls that may affect the kinetics. Results indicate that more than 90% of the anthocyanin adsorption occurs within the first 60 min of exposure to cell wall material. However, desorption appears to occur much faster: a maximum was reached after 30 min. At 15°C, different concentrations of anthocyanins produced small variations in the percentage of adsorption and desorption. At 30°C, higher anthocyanin concentrations had significantly higher adsorption rates. At both temperature conditions, increasing ethanol concentration lowered adsorption rates. The data suggests that eEthanol concentration was the driving factor of adsorption/desorption at lower temperatures, while a dynamic relationship between the three independent variables drives the processes in higher-temperature environments.
Funding Support: E & J Gallo Winery