What makes soda fizzy?
Quick answer
Fizzy drinks get their bubbles from carbon dioxide (CO₂) gas that’s dissolved in the liquid under high pressure when the drink is sealed. Opening the bottle releases the pressure, so the gas can no longer stay dissolved. It escapes as bubbles, which form on tiny scratches or specks called nucleation sites.
Pressure keeps the gas in
Factories pump CO₂ into chilled drinks at several times normal air pressure and seal them quickly. According to Henry’s law, the amount of gas that dissolves in a liquid depends on the pressure above it. Remove the pressure, and the extra gas begins to escape.
That “psst” sound when you open a can is CO₂ rushing out of the space at the top.
Where bubbles start
Bubbles don’t appear out of nowhere. They grow from nucleation sites:
- Tiny scratches in a glass
- Specks of dust or fibers
- Ice cubes, sugar grains or a straw
This is why Mentos dropped into diet cola cause a geyser: their rough, pitted surface creates thousands of nucleation sites at once.
Why soda goes flat
| Factor | Effect |
|---|---|
| Warmth | Warm liquids hold less gas, so warm soda goes flat faster |
| Open container | Gas keeps escaping until it balances with the air |
| Shaking | Creates many tiny bubbles that rush out when opened |
| Wide glass | Larger surface area lets gas escape faster |
Keep opened bottles cold and tightly capped.
The tangy taste
Some dissolved CO₂ reacts with water to form carbonic acid, a weak acid. It gives fizzy drinks their slight bite and makes them mildly acidic; see what the pH scale is.
Who invented fizzy water?
English scientist Joseph Priestley invented a way to carbonate water in 1767, by hanging a bowl of water above a beer vat in a brewery in Leeds. Swiss-German Johann Jacob Schweppe began selling carbonated water commercially in the 1780s.
Natural fizz
Some spring waters are naturally sparkling, picking up CO₂ from volcanic rock underground. Champagne, beer and kombucha get their fizz from fermentation, when yeast produces CO₂; the same gas makes sourdough bread rise.
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