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Five minutes of fame -and lots of bubbles!

Helen writes:

Via a tip off from ‘helpful’ friend and Drivetime devotee I found myself  chatting to Simon Mayo on Monday evening. I was the champagne ‘expert’ for his ‘homework sucks’ spot on Drivetime. I was there to explain why champagne bubbles always rise from the bottom of the glass. I thought I knew my stuff about condensation nucleation but Simon posed some tricky questions ( a physics professor may have been better placed to give the answers in fact) and when I got off air I promised myself to look deeper into the world of champagne bubbles!

Below I outline my findings. It’s an area of great complexity and the research continues.

Initially I explained to Simon that bubbles always rise in champagne because they have their own buoyancy they’re lighter than the liquid they’re in basically. Tiny pockets of carbon dioxide collect at sites of imperfection in the glass called nucleation points. It’s these points that encourage a  pocket or dome of carbon dioxide to gather. The dissolved carbon dioxide collects in the pocket until it can hold no more, whereupon some gas is expelled. This gas forms another bubble which adheres to the outside of the imperfection, then that bubble collects Co2 and grows. Eventually that bubble breaks free from the defect and rises through the champagne, so that’s why you see a string of bubbles rising. This whole process has the grand name of condensation nucleation (thanks to wikinews.org)

A very readable article in Chemical Science called ‘Instant insight: Lovely bubbly’ is by Gérard liger-Belair a professor of chemical physics who studies champagne bubbles in great depth!  (full text here) Did you know that champagne bubbles only travel at about 0.5km an hour, comparable to the speed of a turtle! Yet the release of carbon dioxide as you open a bottle of champagne means the cork can reach speeds of 50-60km an hour!

Simon asked me what would happen to the bubbles if the glass was completely free of imperfections and dirt – after trawling the web this is the most succinct answer I’ve managed to find – HowEverythingWorks.org read the full answer here

If there were no impurities or imperfections in a glass of champagne, bubbles would only form through statistical fluctuations—random effects would occasionally bring enough gas molecules together to form (nucleate) a bubble and that bubble would grow and rise to the surface. But such spontaneously nucleated bubbles are extremely rare and form randomly throughout the fluid, rather than in chains of steady bubbles. In fact, bubbles would be so rare in this impurity-free liquid that you would probably not even notice them—the champagne would slowly go flat by losing gas molecules from its surface alone.

So there you have it! There would very probably be no bubbles.

Simon then wondered why bubbles from lemonade collect on the sides of the glass. Actually they don’t! Pour lemonade into a glass or champagne flute and they behave in the same way as champagne bubbles! It is a known fact however that when fizzy drinks are served in polyethylene terephthalate or “PET” plastic cups, the plastic keeps the fizz in and provides maximum bubbles on the inside surfaces of the container, more so than glasses do. (see factoidz)

So what causes the string of bubbles in the centre of a glass of champagne?

In real champagne, chains of bubbles do rise upwards from the center of the fluid. These bubbles are clearly forming at suspended impurities. All it takes is a tiny piece of dust to trigger bubble formation. If you swirl the champagne slightly, you should be able to see these suspended chains of bubbles move, indicating that the impurities that are triggering them are also moving with the fluid. (thanks again to HowEverythingWorks.org !!

I found another explanation about why bubbles appear to originate from one spot on the Naked Science Forum from Chris who lectures at Cambridge University read full answer here

He says it’s all about:

surface tension and bubble nucleation. Water is a very sticky molecule because it forms electrical interactions between adjacent molecules called hydrogen bonds. This makes it very difficult for a nascent (newly forming) bubble to prise the water molecules apart sufficiently to allow the bubble to remain in existence. This collapsing force is the surface tension.

This means that bubble formation will tend to occur where there is naturally already an imperfection in the way the molecules of liquid are interacting with each other. So a slightly rough or sharp region of the glass wall in a champagne flute for example. Here the bubbles find it slightly easier to form, so they originate at this point preferentially. Once a small bubble has formed then gas can move out of the drink very readily to join and swell the newly formed bubble, which rises to the surface and pops. Chris

Any of you out there with science degrees? Read this!

Hope this throws some light on the magical world of bubbles!

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