Occasionally you may come across a bottle of wine that contains tiny crystal shards that could appear as tiny pieces of broken glass. These are tartrates that are often referred to as wine diamonds. Although they may cause a slight gritty texture on your tongue, they are harmless and safe to consume.
These wine diamonds may occur if the wine has been exposed to temperatures below 4°C, when potassium and tartaric acid, both naturally occurring products of grapes, bind together to form a crystal.
Tartaric acid is used to maintain a wine’s body, character and colour but many wines contain a surplus of the acid, which accounts for the appearance of the wine diamonds. Potassium, which is another big component in wine, binds with the acid and creates a salt called tartaric bisulfate, which separates from the wine and creates the crystals that are found at the bottom of the wine bottle or on the underside of the cork.
The colour of these crystals is dependent on the pigment of the wine. In red wine they will often appear brown or dark red. In white wines they will often look brownish or resemble glass.
It is difficult to predict which wines will have high levels of tartaric acid and thus have wine crystals. Weather, region, soil nutrients and grape varieties all play a role in determining the amounts of acid present in a particular grape.
Older wines are more likely to form crystals or sediment once the cork is removed. As wines are constantly evolving during the aging process, elements within the wine are constantly interacting with each other. As such, some chemical bonds that are formed in the bottle are denser than the wine itself, causing them to sink to the bottom of the bottle. This is part of the aging process.
The presence of wine diamonds is considered by many winemakers as a sign of high quality because it means that the wine was not over processed.
Although wine diamonds may leave a slight gritty texture on your tongue, they do not impact the taste of the wine nor do they pose a health risk. They are completely safe to drink.
If you prefer not to serve wine crystals in your wine you can decant the wine by simply pouring the wine through a wine strainer or cheesecloth into a wine decanter.