Why would a bottle of red wine bubble over like a bottle of Champagne? Was it flawed?

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Dear Dr. Vinny,

I bought a bottle of red wine, vintage 2018. On opening, the wine bubbled over like a shaken-up bottle of Champagne or a fizzy drink (and in the process ruined my cream carpet). What caused this?

—Alasdair, London

Dear Alasdair,

First, I have some advice for cleaning your carpet, which hopefully isn't ruined—good luck!

On to your question, some red wines are intentionally fizzy, like Lambrusco or sparkling Shiraz, but I’m guessing that’s not what you were opening. Fizziness is caused by gas, which is almost always carbon dioxide—a natural byproduct of fermentation. Some wines are bottled with a little bit of carbon dioxide, either trapped in the bottle, or added for freshness and to protect a wine from oxidation before bottling. In these cases it’s just a temporary effervescence that usually dissipates with a swirl or two.

But all the carbonation that you’re describing sounds like the wine started re-fermenting in the bottle, and that’s a flaw. The wine won’t make you sick, but I’m guessing it was a bit stinky and yeasty. Some bacteria could have been introduced, or some residual sugar was left and started a second fermentation. Unfiltered wines, or wines that did not go through malolactic conversion might be more susceptible to fermenting in the bottle.

—Dr. Vinny

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