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What makes some drinks fizzy?

Bubbles of carbon dioxide in a carbonated drink Bubbles of carbon dioxide in a carbonated drink The fizz in a drink is caused by a mass of tiny bubbles rising up through the liquid. These bubbles contain gas that was dissolved in the liquid, but is now escaping. The gas is carbon dioxide (CO2)—which is why these drinks are also called carbonated drinks. As you drink, the carbon dioxide produces a tingling sensation on your tongue and in your throat. Soft drink manufacturers force carbon dioxide and water into the drink at high pressure. The hissing sound you hear when you open a can or bottle (or the loud pop made by opening a bottle of champagne) is produced by millions of carbon dioxide molecules bursting out of the liquid—the result of a rapid loss of pressure. An unopened drink is bubble-free because the pressure inside the can or bottle keeps the carbon dioxide dissolved in the liquid.

A Diet Coke and Mentos eruptionA Diet Coke and Mentos eruptionManufacturers force CO2 into water at high pressure until it is supersaturated—more CO2 is dissolved in it that would be possible under normal, lower pressure conditions. The molecules of water H2O form “cages” around the CO2 molecules, preventing them from escaping. The water is now carbonated. Syrup and flavourings are added and the mixture poured into a bottle or can, which is then sealed. This keeps the pressure high inside, so that the CO2 molecules are held in their molecular cages until the bottle or can is opened.

In order for the gas to break free from the liquid, it has to overcome the force holding the liquid together. Shaking up the liquid adds more energy. The result is that many more tiny bubbles are released, and the liquid erupts with great force out of the can or bottle. A victorious Grand Prix winner shakes up a large bottle of champagne to achieve this effect deliberately.

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