Abstract
Phenolic extraction is a critical part of red wine making. Though empirical models of phenolic extraction kinetics exist, the current level of mechanistic understanding does not allow for accurate predictions. In this work, we propose a mechanistic model for the extraction of phenolics from grape skins and seeds as a function of temperature and ethanol. This model examines the release of phenolics, the adsorption of phenolics onto grape material, and the disappearance of anthocyanins from solution. Additionally, we performed epifluorescence microscopy to explore our finding that seed tannins’ release rate appears independent of concentration, and found that the grape seed appears to ablate over fermentation. We also determined the activation energy of anthocyanin disappearance, in good agreement with similar systems. The proposed model results in an excellent fit, and increases the understanding of phenolic extraction and the ability to predict and optimize product outcome in red wine making.
Highlights
Phenolic extraction is of critical importance to red winemaking
Lerno [2] found that phenolic extraction rate and final phenolic profile are strong functions of temperature, with the fraction of seed-derived tannins increasing with temperature
Final phenolic extraction was found to be a weak function of cap management, as determined by Lerno [3]
Summary
Color (anthocyanins) and mouthfeel (tannins) are extracted from grape skins and seeds over the course of fermentation [1]. Lerno [4] found that extraction of phenolics from grape solids was found to slow down between mixing events in the fermenter and speed up after mixing, indicating a diffusion driven process. These studies are critical to develop a mechanistic understanding of phenolic extraction, but do not allow for quantitative predictions or simple extrapolation to larger industrial systems
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