Raw and first derivative (Δ) UV-VIS absorbance – % transmittance spectra of Mexican monovarietal Merlot wines (samples 3 (red spectra), 6 (blue spectra) and 10 green spectra); see Materials and Methods) at three different pH values (pH = 1, extreme Left; pH = 3.9, Middle; pH = 7, extreme Right). Relevant absorption-%Transmittance peaks at 715 nm is highlighted with a dotted-line circle.