Predicting the Impact of Fermentor Geometry and Cap Management on Phenolic Profile Using a Reactor Engineering Model

Abstract

Understanding of phenolic extraction during fermentation has long been limited to either empirical studies or well-mixed models, which limits the ability to predict the impact of winemaking decisions on final wine phenolic profile. We have developed a combined phenolic extraction and fermentation model that accounts for the heterogeneous nature of red wine fermentations and fermentor geometry by combining previously derived and validated red wine models. Here, we apply this model to explore the impact of fermentor volume and cap management on anthocyanin, skin tannin, and seed tannin extraction. Results indicate that larger, hotter fermentors favor faster extraction, and pump-over frequency strongly affects extraction of anthocyanins, skin tannins, and the relative contribution of seed and skin tannins. At small scales, this variation was not observed, in agreement with experiments. These results suggest potential winemaking strategies to control the ratio of skin to seed tannins in the final wine. Additionally, we explored the impact of fermentor geometry on anthocyanin extraction in the absence of cap management. The ratio of cap surface area to bulk liquid volume was critical in determining the concentration of anthocyanins in the bulk liquid, shedding light on conflicting small- and large-scale results of liquid anthocyanin concentrations without cap management.