What are these white crystals on the bottom of my cork?

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Dear Dr. Vinny,

I’ve found some corks that have some sort of glass (it looks like sea salt) attached to the end that is in contact with the wine. I have found no defects in the precious liquid that’s kept in these bottles. Could it be an effect of preservation at temperatures below 50 degrees?

—Alfredo O., Mexico

Dear Alfredo,

Sounds like you’ve come across tartrate crystals. They’re completely harmless, odorless and tasteless, and they’re a natural occurrence in winemaking. They’re made of the same stuff as cream of tartar, which you might have used when baking.

You’re right that cold temperatures have something to do with these crystals showing up. In fact, when wineries want to remove the sediment (purely for cosmetic reasons), they go through a process called “cold stabilization,” in which the wine is chilled severely and the crystals removed.

Though the crystals are harmless, they can be disconcerting. If you see some sitting at the bottom of the bottle, you can decant the wine to rid them before serving.

—Dr. Vinny

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