Non-invasive quantification of phenol content during red wine fermentations

Abstract

Phenolic compounds are responsible for the most important red wine quality attributes. Anthocyanins and tannins play crucial roles in color and mouthfeel properties of red wines. Phenolic analysis in the winery is hindered by analytical constrains. The possibility to quantify phenolic content non-invasively from a fermenting tank will provide phenolic data in real time and with absence of sampling. This could be achieved by making use of the fluorescence properties of phenolic compounds. Front-face fluorescence was in this case used to obtain fluorescence spectral properties of wines directly during the fermentation tank. Adapting the sample geometry, direct measurement from a fermenting tank through a crystal window can be obtained. Moreover, the fluorescence spectral properties were correlated with phenolic levels using machine learning techniques and accurate spectral calibrations were obtained for total phenol content, anthocyanins (mg/L) and tannins (mg/L). A prototype device for the measurement of fluorescence spectral properties was developed. The fluorescence spectrometer showed the ability to quantify phenolic content during red wine fermentations with the absence of sampling and in a non-invasive manner.