Have you ever heard of anyone finding clear glass like crystals in the bottom of their wine glass or bottle? Perhaps you've even found them yourself?
Don't panic, you've not found glass, you've found tartrate crystals or what winemakers sometimes term 'wine diamonds'.
Let me explain... Both tartaric acid and potassium are naturally found in grapes. During the winemaking process they bind to form a compound called potassium bitartrate. This is the same as cream of tartar used in your cooking at home.
Potassium bitartrate can become unstable at cold temperatures and can sometimes form clear, glass like crystals in wine. These crystals or 'wine diamonds' are perfectly harmless and if ingested will cause no ill effect, possibly only a slight grittiness on the tongue.
Although harmless, many winemakers, including ourselves, cold stabilise their wines. This process drops the temperature of the wine close to freezing for 3-4 days causing the crystals to separate from the wine and stick to the sides of the tank. We then drain the wine from the tank, leaving the tartrate crystals behind and hopefully preventing tartrate dropout. The process is not 100% foolproof and sometimes tartrates are left behind and can crystallise in the bottle at cold temperatures.
Tartrate crystals are more likely to be seen in white wines as opposed to reds because we generally don't chill reds.
So, if you ever find crystals in the bottom of your glass of wine, smile to yourself and count yourself lucky - you've found diamonds!