Why are the corks of sparkling wine mushroom-shaped?

Friends who have drunk sparkling wine will definitely find that the shape of the cork of sparkling wine looks very different from the dry red, dry white and rosé wine we usually drink. The cork of sparkling wine is mushroom-shaped. .
Why is this?
The cork of sparkling wine is made of mushroom-shaped cork + metal cap (wine cap) + metal coil (wire basket) plus a layer of metal foil. Sparkling wines such as sparkling wine require a specific cork to seal the bottle, and cork is an ideal sealing material.
In fact, before being stuffed into the bottle, the mushroom-shaped cork is also cylindrical, like the stopper for still wine. It’s just that the body part of this particular cork is usually made from several different types of natural cork and is then glued together with an FDA-approved glue, while the “cap” part that overlaps the body is made of two. Composed of three natural cork discs, this part has the best ductility.
The diameter of a champagne stopper is generally 31 mm, and in order to plug it into the mouth of the bottle, it needs to be compressed to 18 mm in diameter. And once it’s in the bottle, it continues to expand, creating a constant pressure on the neck of the bottle, preventing the carbon dioxide from escaping.
After the main body is tucked into the bottle, the “cap” part absorbs the carbon dioxide escaping from the bottle and begins to expand slowly, and because the “cap” part has the best extensibility, it ends up in a charming mushroom shape.
Once the champagne cork is taken out of the bottle, there is no way to put it back on because the body of the cork also naturally stretches and expands.
However, if a cylindrical champagne stopper is used to seal still wine, it will not expand into a mushroom shape due to the lack of the stimulating effect of carbon dioxide.
It can be seen that the reason why champagne wears a beautiful “mushroom cap” has something to do with the material of the cork and the carbon dioxide in the bottle. In addition, the beautiful “mushroom cap” can prevent the leakage of wine liquid and the leakage of carbon dioxide in the bottle, so as to maintain the stable air pressure in the bottle and maintain the flavor of the wine.