Pressure, closure sequence & the punt
Six things the pressure decides about this bottle.
Fully sparkling wine typically sits at around 6 bar and may be as low as 5, and EU wine regulation defines sparkling wine as anything above 3 bar. That pressure, held for years through a second fermentation in the bottle, is what makes champagne glass heavy, its punt deep and its finish unlike any still wine bottle.
Six bar is the design condition, not a maximum
A fully sparkling wine typically carries around 6 bar of internal pressure, and the bottle holds it continuously for the months or years the wine spends on its lees. That is a sustained load rather than a momentary one, and it is why champagne glass is specified by weight and wall distribution rather than by capacity alone.
The punt is structural before it is traditional
A deep punt turns the base from a flat plate into a dome, which carries internal pressure far better and removes the sharp internal corner where stress would otherwise concentrate. It also gives a place for the hand during pouring and collects sediment before disgorgement, but the pressure argument is the one that fixed the shape.
The bottle wears two closures in its life
During the second fermentation and aging the bottle is closed with a crown cap, which is cheap, gas-tight and easy to remove for disgorgement. Only afterwards does it receive the mushroom cork and the wire muselet. The finish therefore has to accept both, which is a requirement no still wine bottle carries.
The muselet exists because the cork alone will not hold
At 6 bar a mushroom cork would be pushed out of the neck, so a wire cage holds it down. That cage is a functional restraint rather than a decoration, and the bottle's neck profile has to give the wire something to grip beneath the lip. Removing the muselet from a chilled bottle is what the whole assembly is designed around.
Sparkling is defined by pressure in regulation
EU wine rules treat any wine above 3 bar as sparkling, which sets a legal boundary between a lightly petillant style and a fully sparkling one. Producers working near that line need to know which side of it their pressure sits on, because it changes the labeling as well as the bottle they must use.
The weight is not negotiable in the way still wine glass is
Still wine bottles have been lightweighted substantially in the last two decades. Sparkling bottles have far less room to follow, because the glass is doing structural work. Where a lighter sparkling bottle exists it comes from better glass distribution rather than simply less glass, and its pressure rating is stated rather than assumed.
