Portable photometer for procyanidins quantitation in red wine

The present work introduces a portable photometer to estimate tannin content in red wines. The theoretical premises are based on the known reactivity of wine tannins (procyanidins) with proteinaceous matter which reaction results in a turbid formation of floating procyanidin-protein complexes. The optical device operating with a wavelength-sensitive pulsed electromagnetic source enabled to measure the degree of turbidity, combining the different intensity and spectral emission of a light source with the photodiode wavelength sensitivity. Twenty-seven red wines (tannins content range: 6-1904 mg/L) were optically analyzed soon after adding a saturated solution of gelatin (12% ethanol, pH 3.5). The photometer output signal is a waveform (voltage, V) produced and modified as a function of peak intensity, amplitude, and curvature which depends on the turbidity. Nonlinear correlation fitted the relationship between signal waveform and tannins content (R2 up to 0.966). The proposed photometer is easy to use, cost-effective and provides a reliable alternative to the time-consuming analyses for fast in-line and offline analysis of procyanidins in wine.