Why do Champagne bottles have mushroom-shaped corks?

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Champagne corks

Carter Connelly, from Massachusetts, asks: Why do the corks in Champagne bottles have a mushroom shape, while the corks in still wine bottles do not? The bottle necks aren’t so different.

Dr Paulo Lopes replies: The mushroom shape develops because the cork absorbs the carbon dioxide in the bottle – the pressure in a bottle of sparkling wine is six to eight bars, which makes it a very different environment to a still-wine bottle.

The cork discs on the bottom of a sparkling wine cork are more elastic than the cork granules which make up the rest of the cork, so they absorb the CO2 and expand much more than the granule part, hence the mushroom shape.

If you put still wine in a Champagne bottle, the Champagne corks will never form the mushroom shape.

This phenomenon has practical implications for sparkling wine storage.

To optimise the cork’s mushroom shape, Champagne and sparkling wine bottles should always be stored upright.

Dr Paulo Lopes is an oenologist at Amorim, the world’s largest cork manufacturer.