A carbonated drink tastes different from the same liquid flat, and the change goes well beyond fizz on the tongue. Dissolved gas alters both chemistry and sensation.
Dissolved gas makes a weak acid
Carbon dioxide forced into water does not simply sit there as bubbles. A portion reacts with the water to form carbonic acid, which lowers the pH of the drink.
That acidity is mild but real, and it sharpens the drink in the same direction a squeeze of citrus would, without adding any citrus flavour.
Which is why a flat cola tastes cloying while the same liquid fizzy tastes balanced. The sugar has not changed; the acid holding it in check has escaped.
The tingle is partly a pain signal
The prickle of carbonation is not registered only as touch. Nerve endings in the mouth that respond to irritants also respond to the acid formed at the surface of the tongue.
The sensation therefore sits alongside chilli heat and mustard sharpness in the category of chemical irritation rather than pure taste.
That explains why heavy carbonation can feel harsh rather than refreshing, and why the same drink feels gentler once some gas has come out of solution.
Bubbles push aroma upward
Aroma compounds reach the nose from the drink's surface and from the back of the throat while swallowing. Rising bubbles carry volatile molecules with them as they leave.
A carbonated drink therefore delivers its aroma in bursts as bubbles break, rather than in the steady release of a still liquid.
Open a bottle that has gone flat and the smell is muted long before the taste seems wrong, because the transport mechanism has stopped.
Temperature governs how much stays in
Gas dissolves more readily in cold liquid than in warm, which is why a chilled bottle holds its fizz and a warm one foams over on opening.
As a drink warms in the glass, gas leaves continuously, so acidity falls and perceived sweetness climbs over the course of the same serving.
A drink formulated to taste balanced when cold will usually taste sweeter than intended by the time it reaches room temperature.
Home carbonation has limits
Home systems carbonate plain water well because water has nothing competing for the gas. Adding syrup afterwards keeps the fizz where it belongs.
Carbonating a liquid that already contains sugar, pulp or fat tends to produce vigorous foaming, since those particles give bubbles somewhere to form and escape.
Juices and dairy drinks resist carbonation for that reason, and commercial versions rely on filtration and pressure control rather than a simple gas charge.