“Why do bubbles stick to the straw in fizzy drink?”
My niece had come up with the question after watching bubbles dance around in a glass of soft drink. For a seven year old, this was a pretty good question. My sister (who also has scientific inclinations) was unable to give her a convincing answer, and knowing that I’m a sucker for trying to solve anything remotely scientific, she turfed it to me…
I looked into it and gave her my best answer. I also discovered that the science of bubbles is pretty interesting (no really). So if you’ve ever wondered about how and why bubbles form in a glass of soda/champagne/beer then read on!
Enter the fascinating & bubbilicious world of fizzy drinks…(with some stuff even seven year olds will enjoy)!
Where do bubbles in a drink come from?
I think that watching bubbles in a glass of champagne has a mesmerising effect, a bit like watching the movement of flames in an open fire. But where do those bubbles come from? Why does shaking a bottle of coke before opening it cause an explosion of sugary drink?
Invisible to our eyes, all water contains dissolved gases. Take river water, if it didn’t contain oxygen fish wouldn’t be able to ‘breathe’. Most liquids only contain tiny amounts of gas, but you can squeeze more gas into a liquid in a process called ‘supersaturation’. Anyone remember Sodastream?
Those devices were all the rage in the 1980’s, and they let you carbonate juices to make your own fizzy pop by squirting compressed gas (carbon dioxide) into your chosen beverage. We had one when I was a kid, and I loved it; although if you kept pushing the ‘gas’ button it started to make a funny noise that sounded like something would explode!
If you don’t happen to have a Sodastream, you could always just try to get hold of a cylinder of carbon dioxide (although I doubt Tesco’s stock them) and try this novel way of ‘supersaturating’ water (just don’t try this at home kids)…
The Life of a Bubble
Carbonated drinks are bottled under high pressure. Opening the bottle releases the pressure that is keeping the carbon dioxide gas dissolved, and with a tell-tale ‘psssst!’ bubbles are brought into existence.
But bubbles can’t form just anywhere: These delicate things are rather choosey about where they call home! They prefer to start their microscopic life on any uneven surface. Tiny scratches, irregularities or bits of dust and dirt are good enough!
In the few seconds after opening a bottle, bubbles start to grow at these ‘nucleation sites’. When they grow too big, they will float off toward the surface. The bigger the scratch or bump is then the longer the bubble will be able to ‘hold on ‘; just like how a climber can hold onto an irregular surface for longer than a smooth surface. A bubble will rise to the surface (and pop), unless it hits into another ‘sticky’ nucleation site.
You can test all this for yourself with two wine glasses, some fiz (e.g. champagne or fizzy drink) and some sugar. Sprinkle sugar into one glass and then pour drink into both:
But what about shaking before opening?
Get a bottle of fizzy drink and give it a good shake! I dare you…
If you’ve done this then look closely at the inside the bottle (don’t open it – d’uh)! You’ll see that your mixing has caused a few bubbles to form on the inside of the bottle. There will dozens more microscopic bubbles that you can’t see. And each one of these bubbles acts as ‘nucleation site’, so when you open the bottle and literally millions of bubbles will explode into existence around each!
And we all know what happens next…
Fun Stuff to Try with Kids (big and small):
A can-tapping experiment for slightly older kids
Read More about bubbles:
A Video of how soft drinks are made (from Youtube)
Learn about how champagne is made (from Youtube)
All about Nucleation Sites (Wikipedia article)
An excellent book “How to Fossilise Your Hamster” by Mick O’Hare has more fun things to do with bubbles!