Tartaric acid and potassium naturally occur in grapes. However, when exposed to cold temperatures, they bind together and form potassium bitartrate crystals. These crystals, sometimes referred to as wine diamonds, can be mistaken for small pieces of glass, but pose no danger.
Winemakers often cold stabilize a wine to remove these crystals in an effort to improve clarity. After fermentation is complete, the wine is brought down to 4.5 degrees C for several days, forcing the crystals to form. The crystals stick to the side or precipitate to the bottom of the vessel. The wine is then carefully racked into a clean vessel, leaving the crystals behind.
In addition to improving clarity, cold stabilization accentuates brighter, fruit-forward characteristics in aromatic white varietals like Sauvignon Blanc and Viognier. Bypassing cold stabilization and pressing directly into barrel can diminish fruit aromatics but, may contribute to more complexity and a longer finish on the palate.
