Colour evolution kinetics study of spirits in their ageing process in wood casks

Abstract

The colour of alcoholic beverages increases as they are aged in wood casks, due to the oxidation of the extracted phenols and tannic substances. In this paper, sixteen ageing experiments were carried out involving four different types of wood (American oak, French oak, Spanish oak and Chestnut), two toasting intensities (intense and medium toasting) and three initial wine distillates (holanda, wine spirit from a rectification column distillation and wine spirit from double distillation). Our experiments measured the CIEDE2000 colour difference as a control parameter for eight weeks. Four kinetic models were applied to better comprehend the evolution of the colour: Lagergren's first-order model, Peleg's pseudo-second-order model, an intra-particle diffusion model and a parabolic diffusion model. Differences on the non-linear correlation coefficients obtained by the Lagergren's and the Peleg's models show that the extractions are better fitted by the Peleg's model, leading to deduce that the colour obtained in the ageing process of the spirit is a second-order kinetic procedure. Differences between both diffusion models show that colours obtained from holandas are more strongly affected by side-reactions than colours obtained from wine spirits, probably due to their higher content in non-alcoholic compounds. Peleg's parameters show that toasting pre-treatments of wood also affect the kinetics of the colour obtained: intense toasted woods produce intense colours at the beginning of the ageing process, although medium toasted woods seem to produce more colour when equilibrium is reached.