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How do fizzy drinks get their fizz?

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Quick answer

Fizzy drinks are made by chilling the liquid and pumping in carbon dioxide under high pressure, which forces far more gas to dissolve than normally could. The container is sealed to keep that pressure. Opening it lets pressure fall, so the excess carbon dioxide leaves the liquid as rising bubbles.

Fizzy drinks get their fizz from carbon dioxide gas that is forced to dissolve into the cold liquid under high pressure and sealed in. When the bottle is opened the pressure drops, the liquid can no longer hold all that gas, and it escapes as bubbles.

Step by step

  1. The flavoured liquid is cooled, because cold water can hold much more dissolved carbon dioxide than warm water.
  2. Carbon dioxide is injected at several times normal air pressure, forcing large amounts of gas into the liquid.
  3. The bottle or can is sealed immediately so the high pressure inside keeps the gas dissolved during storage.
  4. Opening the container releases the pressure with a hiss, leaving the liquid holding more gas than it can keep.
  5. The extra carbon dioxide gathers into bubbles on tiny surface flaws, which rise and burst, gradually flattening the drink.

Key things to understand

  1. Carbon dioxide dissolves in water much better under high pressure, a relationship described by Henry's law.
  2. Factories chill the drink and inject carbon dioxide at several times atmospheric pressure, then seal the container quickly.
  3. A small share of the dissolved gas reacts with water to form carbonic acid, giving fizzy drinks their slight sharp tang.
  4. Opening the cap releases the pressure, so the liquid becomes overloaded with gas that starts to come out of solution.
  5. Bubbles form at tiny scratches, dust specks or fibres on the glass, then rise and burst at the surface.

Labelled diagram

  1. Chilled liquid

    Cold water is used because it can dissolve more carbon dioxide.

  2. Pressurised CO2

    Carbon dioxide is forced in at several times normal air pressure.

  3. Sealed bottle

    The cap keeps the pressure high so the gas stays dissolved.

  4. Opening

    Pressure drops with a hiss and the liquid becomes overloaded with gas.

  5. Bubbles

    Gas collects on tiny scratches or dust, then rises and bursts at the surface.

How gas gets into and out of a fizzy drink

Real-world examples

  • Goli soda bottles in India are sealed by a glass marble that the internal gas pressure holds against a rubber ring.
  • Home soda makers push carbon dioxide from a small cylinder into a bottle of chilled tap water.
  • Champagne and many beers become fizzy through a second fermentation inside the sealed bottle.
  • A soft drink left open overnight tastes flat because most of its dissolved carbon dioxide has escaped.

Common mistake

✗ Myth: The bubbles in a fizzy drink are tiny pockets of air.

✓ Fact: The bubbles are almost entirely carbon dioxide that was dissolved in the drink under pressure. They appear when that gas comes back out of solution after the container is opened.

People also ask

Why do fizzy drinks go flat?
Once opened, the drink sits at normal air pressure, which can hold far less dissolved carbon dioxide than the sealed bottle did. The extra gas keeps leaving as bubbles and escapes into the air until the liquid reaches balance with the atmosphere. Warmth, stirring and pouring all speed this loss, leaving the drink flat.
Why do bubbles form on the side of a glass?
Carbon dioxide needs a starting point to gather into a bubble. Tiny scratches, specks of dust and leftover fibres from drying cloths trap minute pockets of gas, and dissolved carbon dioxide flows into them. Each pocket grows until it is buoyant enough to break free, which is why bubbles stream from the same spots.
Is carbonated water acidic?
Yes, mildly. A small part of the dissolved carbon dioxide reacts with water to form carbonic acid, which lowers the pH to roughly 3 to 4 in sparkling water. That weak acid causes the pleasant bite on the tongue. Flavoured soft drinks often add citric or phosphoric acid, making them more acidic still.
Why does a warm soda go flat faster?
Gases dissolve less well in warm liquids than in cold ones. A warm drink therefore pushes carbon dioxide out more quickly once opened, so it foams more and loses its fizz sooner than a chilled one.
Why does shaking a bottle make it spray?
Shaking breaks the gas pocket at the top into countless tiny bubbles mixed through the liquid. When the cap opens, those bubbles act as ready-made starting points, so gas escapes all at once and drives foam out.
How do some drinks become fizzy naturally?
In beer, kombucha and some traditional drinks, yeast ferments sugar and releases carbon dioxide inside a closed container. The trapped gas builds pressure and dissolves into the liquid, carbonating it without any added gas.
Why do Mentos make cola erupt?
The candy's rough, pitted surface provides millions of sites where dissolved carbon dioxide can quickly form bubbles. Gas leaves the cola almost instantly, and the sudden rush of bubbles pushes a foamy column out of the bottle.

Part of the guide: Food & Kitchen Science →