I'd like to point out a common misconception related to the Champagne cork. As incorrectly mentioned in the otherwise excellent writeup about the wine, the cork is not mushroom-shaped prior to closure.

The Champagne cork is originally cylindrical but differs from other corks being longer and considerably wider in diameter. More compression is used to insert the cork about 44mm into the bottle, leaving an exposed portion above the neck of bottle for the cage to grip. The conical nature of the inside of the Champagne bottle will result in the lower portion of the cork deforming into a conical shape as the pressure of the wine inside attempts to force it out of the bottle while it is retained from doing so by the wire cage. In my personal experience with sparkling wine, pressure gauges inserted into a random sample of the bottles undergoing second fermentation, the pressure reaches a peak of 6bar (about 80psi) prior to degorgement, enough to deform a cork over an extended period of time

On a final note, recent trends have favoured a twin-top cork, one where the body of the cork utilises agglomerate cork with two discs of natural cork at the top and bottom. Agglomerate cork withstands more pressure while the natural cork in contact with the wine absorbs liquid and expands, improving the seal with the bottle wall.