“Tartrate crystals are as natural to wine as seeds are to a watermelon.”
— Ronn Wiegand, Master of Wine/Master Sommelier
What are tartrates?
Tartrates, affectionately known by industry professionals as “wine diamonds,” are tiny, crystalline deposits that occur in wines when potassium and tartaric acid, both naturally occurring products of grapes, bind together to form a crystal. Tartrates are scientifically known as potassium bitartrate, which is the same thing as cream of tartar used in cooking. They are completely harmless and natural. The formation of wine diamonds is less common in red wines, as their level of tartaric acid is lower, and crystals tend to fall out naturally during the longer barrel-aging process.
Why do wine diamonds form?
Tartrates are a normal byproduct of wine as it ages—but if the wine is exposed to temperatures below 40°F, wine diamonds can form within one week of a wine bottle’s exposure to extreme temperatures (think a bartender’s cold box where beers, wines and juices are all stored at the
same temperature). It is these chilly conditions that make the tartaric acid compounds in a wine naturally combine with potassium to form a crystal.
Why does tartaric acid remain in wine?
All wine contains naturally occurring organic acids (malic and tartaric acids being the primary ones). Malic acid— “malum” is Latin for “apple”—can almost entirely be converted to the weaker acid, lactic, through a bacterial fermentation. Tartaric is the primary acid we taste in all wines; it is essential to a wine’s mouthfeel and balance. Tartaric acid tends to be more stable in wine, unless the wine is exposed to very cold temperature. Ensuring the perfect balance of these acids in a wine while minimizing the chance for wine diamonds to form is truly where art and science converge.
What methods are used to remove tartrates?
A process called cold stabilization is what we use to remove tartrate crystals from white wine. We chill the wine to 0C for about 7 days, with the chiller jackets on our tanks or we can move tanks outside in the winter. This process is timed properly so when we chill the wine
we are also killing off any residual yeasts. Over chilling can strip the wine of some aroma and flavour – so being mindful of chill time and temp is important. This is also another reason tartrates are becoming more commercially acceptable – it’s minimal human intervention; let the wine do it’s thing! Sometimes no matter how much a wine is cold stabilized crystals can still form. There are stabilizing agents that would block the potassium tartrate formation and growth, but our philosophy is to be less invasive with additives – low intervention winemaking.
Do tartrates affect the quality of the wine?
No. Actually, the presence of tartrate crystals is viewed by many winemakers, sommeliers and academics as a sign of quality, indicating that the wine was not over-processed.
How do you identify wine diamonds?
Potassium bi-tartrate can resemble crystalized sugar granules or crystal shards as they fuse together. They may appear as a powdery white (or red) substance at the bottom of a wine bottle. The crystals can also stick to the bottom of the cork or collect together at the bottom of a bottle. If they are stuck to the bottom of the cork and you let them dry, they sparkle and shine – hence the nickname Wine Diamonds.
How should I serve wine that has tartrate crystals?
The best course of action is to take caution while pouring – pouring slowly on a delicate angle will prevent them from getting in your glass. There are filtration pour spouts that can be used, decanting the wine and in extreme cases pouring through a cheese cloth can work. Most of the time the crystals will settle how the bottle is stored (stored upright, they will likely collect on the bottom etc.), so just taking time to pour the glasses will likely be sufficient. Take extra caution near the end of the bottle (or decanter) to avoid them getting in your glass. They are totally harmless if they do get in your glass – it will just be gritty.