Field Notes #10 · How Much Energy Is Stored in a Champagne Bottle?

A bottle of Champagne at 65 psi contains a surprising amount of stored energy. Break the bottle, and that energy can be released very quickly.

We know this because, in the course of product development, we blew up a lot of bottles.

But here's the interesting question:

Which is more dangerous—a full bottle pressurized to 65 psi, or an empty bottle pressurized to the same pressure?

You might reasonably choose the full bottle. After all, it's much heavier. There is more mass to accelerate and considerably more stuff to fly around when things go wrong.

But the empty bottle has something the full bottle doesn't:

a lot more compressed gas.

And that's where things get interesting.

The pressure may be the same, but the amount of compressed gas is not.

In a full bottle, Champagne occupies almost all of the volume, leaving only a small space above the liquid for compressed gas. In an empty bottle, nearly the entire bottle can be filled with compressed gas.

And compressed gas can do work as it expands.

If the bottle suddenly breaks, that expanding gas pushes outward as it races toward atmospheric pressure. The more compressed gas there is to expand, the more energy is available to do that work.

So, at the same pressure, an empty bottle can contain far more stored energy in its compressed gas than a full one.

There's a rather nice way to think about the tradeoff:

Full bottle: less propellant, heavier projectiles.
Empty bottle: more propellant, lighter projectiles.

This wasn't an entirely academic question for us.

We were designing a system that deliberately pressurizes open Champagne bottles to keep them fresh. And with every glass poured, the bottle gets emptier—and the volume of compressed CO₂ gets larger when the bottle is repressurized.

But Champagne makers have been dealing with the hazards of pressurized bottles for centuries.

In the early days of sparkling Champagne, exploding bottles weren't unusual. Cellar workers sometimes protected themselves with wire masks and enormous protective spectacles.

In one account from 1732, 345 of 594 bottles shattered under pressure—more than half the batch.

Modern Champagne bottles are much stronger.

But the energy hasn't gone away.

And neither has the danger to your eyes.

Today, the bottle itself is much less likely to fail. The more familiar hazard is the cork: a Champagne cork can leave the bottle at roughly 30 miles per hour—fast enough to reach an eye one metre away in less than a tenth of a second. Serious eye injuries still occur.

So when we designed a system that would deliberately return an opened Champagne bottle to its original pressure—and would do so again and again as the bottle became progressively emptier—we had another question to answer:

How do you make that safe?

We built a protective enclosure around the bottle.

Then we did what engineers do when they're worried something might break.