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 (R
²
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.