Nucleation studies of potassium hydrogen tartrate in model solutions and wines

The nucleation of potassium hydrogen tartrate (KHT) in water-ethanol model solutions and in wines is investigated by the induction time technique. The results suggest that KHT nucleation in wine is inhibited by natural compounds. The value of the specific surface energy is found to be around 4 mJ m−2, when derived from a mononuclear mechanism and 6.4, 6.7 and 7.5 mJ m−2 when the polynuclear mechanism is used with volume diffusion-controlled, normal and spiral growth, respectively. Complementary experiments made with a potassium ion selective electrode show that potassium ions are partly associated in solution with organic acids, like tartaric acid. Calculation of KHT supersaturation should therefore take into account the fraction of associated potassium. Further experiments are needed to identify all the associated species and to obtain the dissociation constants of their equilibria.