Why Do Fizzy Drinks Fizz?

The chemistry behind bubbles, foam and that perfect pour

As summer hits and you're cracking open a cold can of cola, have you ever wondered why it fizzes so much more when you open it, or why diet drinks foam more than regular ones? The answers lie in chemistry—specifically gas solubility, pressure, and surface tension.

The Science Behind the Bubbles

The fizz in soft drinks is carbon dioxide (CO₂), the same gas that makes champagne and beer bubble. In alcoholic drinks, CO₂ forms naturally during fermentation. In soft drinks, however, CO₂ is added under high pressure in factories.

This idea of dissolving gas into a liquid was first explored in the 1700s. English scientist Joseph Priestley helped pioneer carbonation, and a Swiss watchmaker, Johann Schweppe, turned the idea into a business—creating fizzy mineral water using scientific equipment.

Henry’s Law – Why the Fizz Stays Trapped

At the heart of fizzy drinks is Henry’s Law, which says:

The amount of gas that dissolves in a liquid is proportional to the pressure above it.

So, when the drink is sealed in a bottle or can, high pressure keeps lots of CO₂ dissolved in the liquid. Open it, and the pressure suddenly drops. The gas escapes, forming bubbles and fizz. That’s why drinks go flat if left open.

Real-life link: Scuba divers also experience this. If they rise too quickly, dissolved gases (mainly nitrogen) escape from their blood too fast, causing decompression sickness—"the bends".

Why Shaking a Can Makes It Worse

If you've ever dropped or shaken a can before opening, you'll know the mess it makes. That’s because shaking introduces small bubbles (called nucleation sites) that disrupt the gas-liquid equilibrium. When opened, these help the CO₂ escape faster and more violently.

Diet vs Regular: Why Some Drinks Foam More

Ever noticed diet sodas foam more? That’s because they’re slightly thicker (more viscous), so bubbles rise more slowly and stack up. Also, the sweeteners used don't reduce surface tension as much as sugar, which helps bubbles last longer.

The Best Way to Pour – Chemistry in Action

To make your drink less fizzy and get the best taste:

Wrong way: Pour straight down into the glass. This creates a lot of fizz because the gas escapes quickly from the wide surface.
Better way: Tilt the glass and pour gently down the side. This reduces bubble formation and gives you smoother taste with less foam.

The more fizz that escapes, the more CO₂ you're losing—which affects taste and aroma, since bubbles carry flavour compounds.

Gas in solution is held in by high pressure (Henry’s Law).
Opening the container = pressure drop → CO₂ escapes.
Shaking = more nucleation sites = more fizz.
Diet drinks foam more due to higher viscosity and stable bubbles.
Pouring technique affects fizz and flavour.

Why Do Fizzy Drinks Fizz?

Why Do Fizzy Drinks Fizz?

The chemistry behind bubbles, foam and that perfect pour

The Science Behind the Bubbles

Henry’s Law – Why the Fizz Stays Trapped

Why Shaking a Can Makes It Worse

Diet vs Regular: Why Some Drinks Foam More

The Best Way to Pour – Chemistry in Action

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