Patrick Setford, Richard Muhlack,* David Jeffery, and Paul Grbin
*School of Agriculture, Food and Wine, The University of Adelaide, PMB 1, Glen Osmond, SA, 5064, Australia (richard.muhlack@adelaide.edu.au)

Anthocyanins are a class of chemical compounds found within red grape skins that account for the majority of color in young red wines. During fermentation and over time, these compounds engage in reactions that influence long-term wine stability and aging potential. As a result, understanding the influence of chemical and physical parameters on the extraction and subsequent evolution of anthocyanins is critical for production of red wines with desired sensory properties. The extraction rate and maximum concentration of anthocyanins in a fermenting red must can be controlled by winemakers through specific extraction operations, including mixing, prefermentation cold soaking, and manipulating process variables such as fermentation temperature. To better understand these effects, a factorial experiment was designed to investigate the impact of extraction temperature, ethanol, and solute (sugar) concentration on the extraction kinetics and mass transfer properties of anthocyanin monomers from prefermentative red grape solids. A mathematical model that allows the calculation of mass transport properties in both the liquid and solid phases was applied to the experimental extraction observations to quantify diffusion and mass transfer coefficients at varying conditions. These derived parameters were subsequently applied to simulated red wine fermentations with continuously changing liquid phase conditions. The impact of varying temperatures and mixing regimes was also investigated using simulations to further explore their effect on extraction rate and maximum potential to extract anthocyanins during fermentation. Results from this study could inform winemakers of the optimal process conditions to achieve a desired anthocyanin concentration and may lead to development of new process control systems for winemaking. Application of these simulations could also improve overall efficiency and decrease production costs of a winery by optimizing available tank space and minimizing energy consumption from unnecessary operations designed to extract color from red grapes.

Funding Support: Wine Australia School of Agriculture, Food and Wine, The University of Adelaide