SCIENCE MINUTES “THE CLEAR PICTURE” | Why shaking a soda bottle makes it fizz over

Shaking a soda bottle does not create a large increase in pressure. It creates something else: countless places where carbon dioxide bubbles can form. When the bottle is opened, those bubbles expand so quickly that the drink surges out.

Marek Strandberg explains that soda consists essentially of water with carbon dioxide dissolved in it under pressure. If the bottle remains still in a refrigerator and opens slowly, only a small amount of gas escapes. Most stays in the drink, releasing bubbles gradually as it is poured or consumed.

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Shaking does not increase the pressure in the soda bottle, but the formation of bubbles.

A shaken or jostled bottle starts the bubbling process before it opens. Carbon dioxide bubbles begin emerging from the liquid and attaching themselves to the bottle walls. Once the cap comes off, the outside pressure drops suddenly. Gas then escapes intensely around every bubble already present, making the release hundreds or even thousands of times stronger than when a calm bottle opens.

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The process is initiated.

That is why the bottle can appear to contain extra pressure, even though its internal pressure has barely changed. The difference lies in the number of sites where bubbles can form. The same principle explains the familiar Coca-Cola and Mentos fountain, but in a more extreme form.

Mentos has an extremely rough, porous surface rather than a smooth coating. Its fine texture creates enormous numbers of places for carbon dioxide bubbles to develop. The bubbles form throughout the drink and force gas, along with much of the liquid, out of the bottle. Strandberg stresses that the result is a purely physical process, not a chemical explosion.

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The reaction between Mentos and Coca-Cola is not a chemical explosion, but a purely physical process.