Where Do the Bubbles in Fizzy Drinks Come From?

Step 1 of 5

Liquids can hold gas dissolved, invisibly.

Carbon dioxide molecules fit between the water molecules and simply sit there. An unopened bottle looks completely still because nothing is escaping.

Step 2 of 5

Pressure is what keeps it in.

The factory pushes gas in and seals it. The gas above the liquid presses down hard enough that molecules cannot escape faster than they return.

Step 3 of 5

Opening the bottle removes the lid on the pressure.

That hiss is the pressed gas escaping. Now the liquid is holding far more gas than it can, so the extra has to come out.

Step 4 of 5

Bubbles need a rough spot to start on.

Gas cannot form a bubble in perfectly smooth liquid easily. It gathers on scratches, dust and fibres, which is why bubble streams rise from fixed points.

Step 5 of 5

Warm and shaken both make it worse.

Warm liquid holds less gas, and shaking spreads millions of tiny bubbles through the drink, each one a ready-made starting point.

Mentos work so violently because their surface is covered in microscopic pits — an enormous number of bubble starting points at once.