Identifying Tartrate Salt Crystals in Wine Sediment

Crystalline sediment of potassium hydrotartrate and calcium tartrate in wines is a major problem of wine industry. Reliable identification of crystals can establish the cause of their formation and facilitate appropriate technological solutions. The research objective was to study the morphological features of potassium and calcium salts of tartaric acid via microscopy. The study featured natural crystal sediments that developed in 105 samples of white and red wines over six months after the end of fermentation, as well as when crystallization was provoked by freezing. The microscopic examination involved a Micmed-5 optical microscope and a PHENOMproX scanning electron microscope. Identification of cations in the composition of crystals followed the method of energy-dispersive spectroscopy, as well as the method of quality reaction with sulfate-anion in acidic medium. Co-precipitation of colloidal substances was typical of potassium hydrotartrate. It violated the crystal lattice construction and determined the wine color, polymorphism (truncated ellipsoid → lanceolar → rhomboid → geometrically irregular shapes), surface roughness, and optical opacity. The expressiveness increased with the crystal growth (3–350 μm). Calcium tartrate demonstrated no evolutionary changes; it was morphologically uniform, colorless, and transparent. Its crystals had smooth faces and clear edges, regardless of their size (1–150 μm) and the chemical composition of wine. The research systemized the morphological features of tartrate crystals formed in wines. The obtained results are important for the technochemical control in the process of destabilization diagnosis. The data can be recommended for further studies in applied research laboratories and institutes.