Mathematical modelling of anthocyanin mass transfer to predict extraction in simulated red wine fermentation scenarios.

Anthocyanins are polyphenolic compounds present in grapes that are responsible for the initial colour of red wine and their incorporation into derived pigments leads to long term colour stability. The ability to predict the effect of process variables, either controlled by winemakers or that naturally change throughout fermentation, on the extraction of anthocyanins is vital to producing red wine of high quality. A 23 factorial experiment with additional points located at central factor conditions was used to determine the impact of temperature, sugar and ethanol concentrations on the mass transfer properties of anthocyanins from fresh Pinot noir grape solids. Factor conditions were chosen to replicate ethanol and sugar concentrations that would be found in a 14% red wine and its respective unfermented juice. A previously described mathematical model was applied to anthocyanin extraction curves to determine mass transfer coefficients and distribution constants for the generation of response surface models able to predict these mass transfer variables for dynamic fermentation scenarios. The coefficient of determination for the model solution exceeded 0.94 in all cases, demonstrating a good agreement between experimental and mathematically-derived anthocyanin concentrations. Following this, simulations of anthocyanin extraction under fermentation conditions were conducted using a previously developed wine fermentation model allowing for the prediction of extraction rates and anthocyanin concentrations under various winemaking scenarios. The extraction simulations predicted a previously observed but so far undescribed anthocyanin extraction pattern during fermentation.