Cold stabilization is a process after fermentation used in winemaking to reduce tartrate crystals (generally potassium bitartrate) in wine. During fermentation, these tartrates bind with the lees, pulp debris and precipitated tannins and pigments. While there is some variance among grape varieties and wine regions, generally about half of the deposits are soluble in the alcoholic mixture of wine.
These tartrate crystals look like grains of clear sand, or sugar crystals - and are also known as 'wine crystals' or 'wine diamonds'. They may appear to be sediment in the wine, but they are not. During the cold stabilizing process, the temperature of the wine, after fermentation, is dropped to close to freezing for 3-4 days. This will cause the crystals to separate from the wine and stick to the sides of the holding vessel. When the wine is drained from the vessels, the tartrates are left behind.
The clarification and stabilization of wine in winemaking involve removing insoluble and suspended materials that may cause a wine to become cloudy, gassy, form unwanted sediment deposit or tartaric crystals, deteriorate quicker or develop assorted wine faults due to physical, chemical or microbiological instability.
After bottling, a wine can be exposed to extremes in temperatures and humidity as well as violent movement during transportation and storage that can encourage the wine to go through additional chemical changes that may produce faults or undesirable traits to emerge in the wine. Eliminating suspended particles in a wine can increase the stability of a wine and prevent some of these undesirable characteristic to emerge.
The process of clarification does, in itself, increase the stability of the wine by removing some of these particles. Conversely, the process of cold stabilization can also increase the clarity and brightness of a wine.