Have you ever opened a bottle of wine and found what looked like little crystals on the wine cork or at the bottom of your wine glass? Those completely harmless crystals are tartrate crystals, technically potassium bitartrate, or what some call “wine diamonds.” They occur when tartaric acid, which is found in grapes and various other fruits, binds with potassium under cold temperatures. The reaction, which occurs in both red and white wines, forms a crystalline salt that tends to adhere to corks when the wine is properly stored.
These crystals are more commonly found in red wines because white wines generally are cold stabilized before being bottled. During cold stabilization, the wine is brought down to near freezing temperatures in order to filter out the crystals. Some winemakers do not cold stabilize or filter their wines because they believe it can remove some of the wine’s flavors.
Although the crystals are harmless, you won’t want to drink them because of their texture. However, admire the glittering “diamonds” deposited on the cork as a promise of hands-off approach to winemaking, letting the wine shine with minimal interference from the winemaker.