The Physics That Makes Swing-Top Bottles ‘Pop’

FLORA LICHTMAN: For a lot of us, this is a sound of celebration.

[CHAMPAGNE CORK POP]

It’s also a sound that probably most of us don’t think too much about, until we open our next bottle, anyway. But my next guest has given it a lot of thought. Dr. Max Koch is a physicist at the University of Göttingen in Germany. He does home brewing on the side, and he wondered, what is actually making that popping sound? What’s happening inside that bottle, physics wise? Y’all, the answer is going to crack your mind open. Max, welcome to Science Friday.

MAX KOCH: Hello, hello.

FLORA LICHTMAN: So you’re a home brewer. How did this beverage brainstorm start for you?

MAX KOCH: Actually, I got inspired to do this several years ago, just as a hobby. And I had this ginger beer. It didn’t taste so well, so I didn’t know what to do with it. And on my birthday, I had the idea to film it in our labs with the high speed camera with 16,800 frames per second.

FLORA LICHTMAN: This is exactly how I would imagine a physicist home brewer spending his birthday.

MAX KOCH: [CHUCKLES] Yeah, you are a passionate physicist when you are a physicist.

FLORA LICHTMAN: [CHUCKLES] So you brought it into the lab, and you filmed it.

MAX KOCH: Exactly. And there were actually things that looked pretty interesting and we couldn’t explain from the go, and that’s how we decided to dig in a little bit deeper.

FLORA LICHTMAN: So I want to get into some of your findings. But first of all, what kind of bottle were you looking at? Is this like a home brewing bottle, the kind with the rubber cork and the metal handle, that you used to pop it open?

MAX KOCH: It’s a swing top bottle, so with this metal wire that holds a porcelain top with a rubber sealing.

FLORA LICHTMAN: Kombucha people will know it for sure. So I want to hear the sound. Let’s play it.

[CHAMPAGNE CORK POP]

Is that the sound that you were investigating?

MAX KOCH: Exactly that one. [CHUCKLES]

FLORA LICHTMAN: Is it like music to your ears?

MAX KOCH: It was not loud enough, but yes.

FLORA LICHTMAN: [CHUCKLES] So you filmed it. You hear that pop. What did you find? What was happening inside the bottle?

MAX KOCH: So we recorded it with a camera and also with a microphone that was capable of recording even very high frequencies. So first of all, of course, when the lid lifts off, then the gas is exhaust into the air. And that expansion of the pressurized gas that was kept in the bottle cools down the gas so it can reach down to minus 50 degrees Celsius.

FLORA LICHTMAN: Minus 50 degrees Celsius?

MAX KOCH: Yeah, yeah, yeah, yeah.

FLORA LICHTMAN: That’s like minus 58 Fahrenheit for us here.

MAX KOCH: Exactly, but only for some milliseconds. And if you look with a high speed camera, you might detect even some ice particles.

FLORA LICHTMAN: Really?

MAX KOCH: They don’t live long, like a fraction of a second.

FLORA LICHTMAN: Was that a surprise that it got so cold?

MAX KOCH: Indeed, yes. And the more surprising was the vibration that we saw in the bottleneck, because I filled the ginger beer into white transparent bottles that we could actually see through, and there was something vibrating in the bottleneck after cap liftoff. And eventually, when correlating that with the microphone recordings, we saw that this is actually the source of the sound. So it’s not a shockwave that’s emitted from opening. It’s actually a resonance in the bottleneck.

FLORA LICHTMAN: How loud is the sound?

MAX KOCH: It’s extremely loud. Fortunately, it’s very short. But suppose you could have your ear inside the bottleneck. Then you would hear 180 decibels, which is the same or even more loud as the turbine of an airplane.

FLORA LICHTMAN: It’s as loud as a jet engine?

MAX KOCH: Exactly.

FLORA LICHTMAN: What about how fast the gas– how fast is the gas moving when it comes out of the bottle?

MAX KOCH: Oh, it’s probably supersonic.

FLORA LICHTMAN: There’s a lot going on in that little tiny moment.

MAX KOCH: Exactly. [CHUCKLES] That’s why it was so fascinating, and we finally made a paper out of it.

FLORA LICHTMAN: Is there something special about the swing top, or would we see the same physics when you pop a bottle of champagne or crack open a can of beer?

MAX KOCH: For the can, it might be different because the gas has more time to get out to a more smaller opening. But with the champagne, it’s even more pronounced because when you purchase a champagne bottle, the pressure usually is higher than the one in the beer bottle, so there is even more going on.

FLORA LICHTMAN: Max, please tell me there’s no practical application for this work.

MAX KOCH: [CHUCKLES] There is, of course, practical application.

FLORA LICHTMAN: [CHUCKLES]

MAX KOCH: First and foremost, you need a philosophical topic once you open your beer bottle with your friends, and this is probably where you can start.

FLORA LICHTMAN: That’s what my friends always tell me. “Please explain physics over our beer.”

MAX KOCH: [CHUCKLES] Ah. You’ve got some nice friends there.

FLORA LICHTMAN: Well, cheers, Max. Thank you so much.

MAX KOCH: Yes, thank you so much.

FLORA LICHTMAN: Dr. Max Koch is a physics researcher at the University of Göttingen in Germany, and you can see high speed video of these bottles being uncorked at sciencefriday.com/pop.

Copyright © 2025 Science Friday Initiative. All rights reserved. Science Friday transcripts are produced on a tight deadline by 3Play Media. Fidelity to the original aired/published audio or video file might vary, and text might be updated or amended in the future. For the authoritative record of Science Friday’s programming, please visit the original aired/published recording. For terms of use and more information, visit our policies pages at http://www.sciencefriday.com/about/policies/