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Dear Dr. Vinny,
Upon opening some bottles from my cellar, I've noticed some crystallization on the wet end of the cork. Can you tell what this is, and the cause? Is this a sign of spoilage?
—Steve Davis, Southbury, Conn.
They may look like rock candy or—yikes—shards of glass, but those are actually tartrate crystals clinging to your cork. It's a completely harmless and natural occurrence. Odorless and tasteless, they're made of the same stuff as crème of tartar (which you might cook with).
Some wines go through a process called "cold stabilization" to remove this sediment, although purely for cosmetic reasons. Even though tartrate crystals are harmless, it can be unpleasant to bite down on them, so if it looks like some are sitting at the bottom of your bottle, you should decant the wine to get rid of them before serving.
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