Have you ever opened a bottle of wine and noticed small crystal like flecks in the bottom of the bottle or glass? Worry not, there aren't glass shards in your wine, you've simply found tartrate crystals or, as we prefer to call them, wine diamonds.
So what are wine diamonds and where do they come from?
Wine diamonds are the result of the tartaric acid and potassium naturally found in grapes, combining during the winemaking process to create a compound called potassium bitartrate. Potassium bitartrate is the same the common pantry staple, Cream of Tartar.
When wine is stored at cold temperatures it can cause the potassium bitartrate to become unstable, and form clear, glass like crystals in wine. Given this reaction is activated by cold temperatures, wine diamonds more commonly appear in white wines, but can also occur in red wines.
To eliminate the occurrence of wine diamonds, some winemakers undergo a cold stabilisation process. However, some winemakers also choose to leave wine diamonds in the finished product.
What is Cold Stabilisation?
We asked chief winemaker, Jon Heslop for a layman’s explanation about cold stabilisation and how it affects wine diamonds, and his answer is below.
After fermentation, young wines are usually saturated with potassium bi-tartrate. When a wine is cooled the solubility limit is exceeded and this 'excess' precipitates out as crystals. The lower the temperature to which it is cooled the more crystals will form, until the saturation equilibrium at that temperature and pH is reached. Cold stabilisation lowers the total acidity, and raises the final pH of the wine. At a pH of about 3.6, depending on alcohol content, the solubility of potassium bi-tartrate is at its highest. Either side of this pH the solubility decreases. Our whites will generally be in the 3.15 to 3.40 range.
Soon after the fermentation is complete, we cool the tank to around freezing and hold it at this temperature for a period to allow crystals to form. The crystals stick to the sides of the tank, and the wine is then racked off, leaving the crystals in the tank. Many winemakers argue that a portion of the flavour and uniqueness of the wine is lost with the crystals. Thus, we only gently cold stabilise the wines. You will find much larger commercial wineries will routinely chill the wine to temperatures well below freezing and while this eliminates any chance of crystals forming, it may also remove other desirable compounds in the wine.
Are wine diamonds safe for consumption?
Naturally when wine diamonds are found, we hear you ask "is my wine still okay to drink?" Of course it is! In fact, some winemakers and sommeliers around the world consider wine diamonds to be an identifier of a high quality wine.
Wine diamonds are completely safe to consume, they may just have a slight bitter/acidic taste and grittiness. Whilst wine diamonds are completely harmless, if you find the sight of them in your glass or the feel of them in your mouth unsettling, you can simply decant your wine and filter it through a piece of cheesecloth (or other thin, clean cloth) or even a coffee filter to remove them prior to drinking.
So the next time your come across wine diamonds, don't stress, just relax and enjoy your wine... some people spend their whole life in search of diamonds 💎