Some of our customers have asked us about crystals they find from time to time in their wine, particularly, some of the high quality Cellar Craft Crushed Grape kits. These crystals are known as Wine Diamonds and are nothing to be alarmed about. Wine diamonds are actually tartaric acid crystals.
Tartaric acid, the principal acid in grapes, forms the component that promotes a crisp flavour and graceful aging in wine. When tartaric acid combines with natural occurring potassium ions in your wine they form potassium bitartrates, which are less soluble in alcohol and water. The result… they dropout.
In red wine, these wine diamonds absorb the red or brown pigments from the wine. In white wine they can look like shards of glass in the bottle. Wine diamonds are harmless, do not affect the flavour and really only impact the wine visually.
As a matter of fact, tartrates are routinely found in high quality commercially – produced wine. Some say that is actually a sign of quality. The process of tartrate crystal formation is very hard to predict, but tends to occur more frequently in pure varietal juices.
Wine diamonds can be avoided by cold stabilization. This is done by chilling your carboy to 10C for a week and then filtering. However, quite frankly, this is likely more hassle than it is worth, for the home winemaker. Just tell your friends that diamonds are a wine maker’s best friend, as they show quality. Commercial wine makers commonly cold stabilize to avoid this problem.