Soda fizzes because it’s full of dissolved carbon dioxide gas that escapes as bubbles when you open the container. Those bubbles are what you hear, see, and feel on your tongue.
Dissolved gas under pressure
Inside a sealed can or bottle, soda is made by forcing carbon dioxide (CO₂) gas into the liquid at high pressure, which makes much more CO₂ dissolve than would at normal air pressure. When the container is closed, that high pressure is maintained, so the gas stays dissolved and the drink remains fizzy.
What happens when you open it
When you open the soda, the pressure suddenly drops to normal air pressure, and the liquid can no longer hold as much dissolved CO₂. The extra gas escapes as bubbles that rise to the surface and pop, creating the characteristic hiss and fizz.
Why bubbles keep forming
CO₂ tends to come out of solution at tiny rough spots called nucleation sites, such as scratches on the glass, grains of sugar or salt, or imperfections in the container. These spots help bubbles start, then they grow and detach, so bubbles keep forming until the soda gradually goes “flat” as most of the gas leaves.
The tingly taste
Some of the dissolved CO₂ reacts with water in the soda to form a weak acid called carbonic acid. This carbonic acid gives fizzy drinks their slight “bite” or tangy, tingling sensation in addition to the physical feel of bubbles popping on the tongue.
