Tartrates a.k.a. “Wine Diamonds” – by Rhys Pender

What is this in my wine?

When opening and pouring some of your favourite wines, you may be surprised by the site of small crystals on the bottom of the cork or in the bottom of your glass or bottle. It is easy to be concerned as the crystals can look like ground up glass or sugar crystals. But there is no need to fear, these completely harmless particles are known as wine diamonds or tartrates. 

What are “wine diamonds” and how do they form?

Tartrates, or wine diamonds, are particles that separate from the wine, particularly during ageing in tank and often in bottle if the wine is subjected to cold temperatures. The particles are mostly made up of potassium bitartrate. These natural occurring tartrates are not fully soluble in wine and will therefore precipitate out at some unknown point in time. Higher levels of tartrates can be expected in cooler climates that have naturally higher levels of acidity in the grapes. You may actually be more familiar with these tartrates than you think. If you have ever used cream of tartar for baking, you have actually used the very tartrates that are scraped out of tanks and barrels and that you can sometimes find in your wine. 

What do they look like?

Wine diamonds look like the name suggests, small crystals that form on the bottom of corks or in the bottom of a bottle. In white wines they are usually clear while in red wines they are often stained a reddish brown colour. 

Are they dangerous or do they affect the quality of the wine?

Wine diamonds are completely harmless, tasteless crystals that are a natural part of the winemaking process. You can consume them although they are slightly gritty and flavourless so it is often best to just leave them in the bottle. They also have no negative affect on the quality of the wine. In fact, their very presence is often an indication that the wines have been made more naturally with less winemaker intervention. 

Can’t the winery remove them?

There are winemaking techniques to remove tartrates, however there are some thoughts that these cold stabilization treatments can also affect the taste and aroma of the wine. To make sure the tartrates don’t precipitate in bottle, wines need to be chilled to temperatures as low as -5 to -10°C for a couple of weeks. Essentially, this technique gets rid of any tartrates in the cellar so they can’t form in the bottle. 

How should I serve wine that has wine diamonds?

Once you know what wine diamonds are and that they are harmless, the best serving technique is to simply decant the final part of the bottle or use a filter to remove any of the tartrates.