Measuring wine tannin through pigment subtraction by spectrophotometer

Red wine is a complex mixture containing thousands of compounds. Anthocyanins and proanthocyanidins (PAs) are among the most important contributors to red wine quality, influencing color, astringency, and long-term color stability. During winemaking and aging, PAs undergo structural modifications that produce wine tannins (WTs) and pigmented tannins (PTs). We demonstrate that the Malvidin-3-O-glucoside molar absorption coefficient (ε) is 4.6× that of (-)-epicatechin at 280 nm. Differences in the ε of WTs and PTs were accounted for by manipulating the Bouguer-Beer-Lambert law and correcting the measured 280 nm absorbance for the contribution of pigments. This correction was applied to 24 commercial red wines spanning a range of pigmentation levels. Highly pigmented wines exhibited greater spectral interference than less pigmented wines, leading to corrections in quantification as high as 19% and as low as 1.7%, respectively. This approach improves WT and PT quantification and advances our understanding of stable color development in red wine.