Innovative method for the direct measurement of tannins in red wines

The present work introduces a fast, rapid, and reliable optical method to quantify the tannin content in red wines. Wine samples are directly mixed with a protein solution (gelatin) under controlled pH conditions, resulting in a modification of the optical properties of the mixture. The extent of turbidity arising from the tannin-protein interaction is directly measured with an optical device operating with a wavelength-sensitive pulsed electromagnetic source. Preliminary measures on a selection of commercial red wines showed a high predictive capability in tannins quantitation. The instrumental signal generated by the sample turbidity was modelled as a function of peak intensity, amplitude, and curvature, obtaining a non-linear correlation compared to a colorimetric tannin assay as reference method. Results confirmed the suitability of the method for direct measurement of tannins, overcoming laborious lab protocols; further advantages consist of its affordability and the limited cost of the prototype used for the optical measurements. All these considered, the method can be easily exploited for quality control in the oenological industry, supporting strategies to produce quality wines.