Why does soda fizz?
Soda is filled with carbon dioxide gas squeezed into the liquid under pressure. When you open it, the pressure drops and the gas escapes as bubbles, which form on tiny scratches and specks in the liquid.
Gas is squeezed into the drink
At the factory, carbon dioxide gas is pushed into the cold liquid under high pressure, and the bottle is sealed. Under that pressure, far more gas dissolves than normally could.
Share this stepOpening it releases the pressure
When you twist the cap, the pressure inside drops to normal air pressure. That’s the hiss you hear. Suddenly the liquid holds more gas than it can keep, and the gas starts to escape.
Share this stepBubbles need a starting point
Gas can’t easily form a bubble out of nothing. Bubbles grow on tiny scratches in the glass, specks of dust or fibers, which is why they rise in steady streams from the same spots.
Share this stepFizz is gas escaping its squeeze.
Pressurereleasebubbles
Cold soda holds its gas longer, and warm soda loses it fast. That’s why warm soda foams over and goes flat sooner. The gas also gives soda its slight sour tang.
Common follow-up questions
Why does shaking a soda make it explode?
Shaking creates millions of tiny bubbles in the liquid. When you open it, the gas rushes into all of them at once and pushes the soda out.
Why does soda go flat?
Once the bottle is open, the gas keeps escaping until the liquid can’t lose any more. Keeping it cold and tightly closed slows this down.
Why do Mentos make soda erupt?
The candy’s surface is covered in tiny pits, giving countless starting points for bubbles to form all at once.
Is the gas in soda bad for you?
No. It’s the same carbon dioxide you breathe out. It can make you burp or feel bloated, though.
