Thermodynamic Parameters of Potassium Bitartrate during the Young Wines Cold Stabilization

Abstract

The present work was undertaken to study the effect of the treatment temperature on the potassium bitartrate stability and composition of young wines. The thermodynamic parameters, namely ∆G°, ∆H°, ∆S° were calculated to predict the nature of potassium hydrogen tartrate (KHT) precipitation. According to the achieved results, the exothermal nature and thermodynamical feasibility of KHT precipitation in young wines were established. Based on thermodynamics, negative ∆G°, ∆H° values and positive ∆S° value give a spontaneous KHT process at lower temperatures. Introduction Wine is a complex chemical mixture and its stability depends on the activity of microorganisms and the changes in its environment. Less than half of the found in grapes tartaric acid is free standing, the majority of it being presented as potassium acid salt (KHT, etc.). Once bottled, a wine may cause cloudiness, formation and precipitation of tartaric crystals. Under certain conditions, e.g. storage at low temperature, the dissolved form of KHT become insoluble forming small crystals, which settle to the bottom [1-3]. As it is known, for the commercial distribution of wines in bottles, the wine must not only be clear at the time of bottling, but also must remain in this condition over the time. Numerous effi cient treatment methods for the stabilization of wines are known up to now: cooling [4], cationic exchange [5-6], reverse osmosis, electro-dialysis [7] and the addition of selected additives [8-9]. From the above-mentioned techniques, cooling alone has found commercial application for the tartaric stabilization of young wines. This method involves cooling the wine near its freezing point to encourage the tartrates to crystallize and precipitate out of the wine before bottling. The present study was conducted in order to study the variation of thermodynamic parameters of KHT during the cold treatment of white and red young wines. Our efforts were also directed to the determination of some thermodynamic parameters, which describe the precipitation process at the equilibrium, such as: equilibrium constant, entropy change (ΔH°), enthalpy change (ΔS°) and Gibbs free energy (ΔG°) of KHT precipitation.