What are the white crystals in my wine bottle?

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Dear Dr. Vinny,

I’ve discovered that white crystals have formed in some of my wines. What are they?

—Rupesh. Nepal

Dear Rupesh,

I assure you that it’s perfectly normal to come across crystals that look like chunks of salt or rock candy in your wine. Tartrate crystals are a harmless, naturally occurring byproduct of winemaking; they might taste a little sour if you try eating them. They typically collect on the cork or at the bottom of a wine bottle. They are sometimes referred to as “wine diamonds,” a lovely way to try to convince people not to worry about them. Another way to consider their harmless nature is to remember that they’re the same substance used to make cream of tartar, which keeps my snickerdoodle cookies light and airy.

Tartaric acid is one of a few types of acid found in wine grapes. Through the process of fermentation and winemaking, it tends to settle out of the wine. They're sensitive to cold temperatures, and some wines actually go through a “cold stabilization” process to separate the tartrate crystals out before bottling. Sometimes wine drinkers might confuse them for broken glass, so it’s just a cosmetic treatment.

—Dr. Vinny

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