How carbonation changes the way a beer tastes on the tongue

Carbonation has a taste of its own

Dissolved carbon dioxide forms a little carbonic acid in beer. When it reaches the tongue, part of the prickle you feel is detected by the same taste cells that sense sourness. Researchers identified an enzyme on those sour sensing cells that turns CO2 into acid right at the surface. The rest is a physical tingle as bubbles burst against the tongue and the nerves that sense touch and irritation respond.

That is why a highly carbonated beer has a clean, slightly sharp bite even when it contains no acid of its own. Soda water tastes of something for the same reason.

How much CO2 is in a typical beer

Brewers measure carbonation in volumes: the volume of CO2 gas dissolved per volume of beer. A rough guide by style:

• Cask ale: around 1 to 1.5 volumes. Soft and gentle.
• Most lagers and pale ales: around 2.4 to 2.7 volumes. Lively but not aggressive.
• Hefeweizen and many Belgian ales: 3 volumes or more. Big, mousse-like foam and a sharp prickle.

The same recipe at 2.0 and at 3.0 volumes tastes noticeably different. Brewers choose the level on purpose. It is part of the style, not an accident of packaging.

Fizz lifts the aroma

Rising bubbles carry aroma compounds out of the beer and into the air above the glass. A well carbonated beer delivers hop and yeast aroma to your nose with every sip and every swirl. Let the same beer go flat and the aroma drops away, because nothing is pushing volatiles to the surface.

This works inside the mouth too. CO2 coming out of solution on the tongue carries aroma up the back of the throat to the nose. That retronasal route is a big part of what you call flavour. Our guide to smelling a beer properly explains how to use both routes.

Why a flat beer tastes sweeter and heavier

The bite of carbonation pushes against sweetness. Take it away and the beer tastes sweeter, softer and fuller than it did. That is partly why a beer left in the glass for an hour seems cloying. It is also why a lightly carbonated beer can feel richer than the same recipe with more fizz.

Carbonation also interacts with bitterness. The prickle and acidity from CO2 add to the sharp impression of a hoppy beer, while some drinkers find a very fizzy beer harder to taste through. Body changes too: higher carbonation makes a beer feel lighter and thinner on the tongue, while low carbonation leaves it rounder. Our guide on why beer tastes sweeter as it warms covers the temperature side of the same effect, since warm beer also loses CO2 faster.

Draught, can and the bar in between

The carbonation you taste depends on what happens after the brewery. On draught, the gas pressure and temperature in the keg set the level. If a bar runs its kegs too warm with the wrong pressure, beer can pour over carbonated and foamy, or go flat in the line. A beer at 2.6 volumes in the brewery can reach the glass noticeably higher or lower if the system is set badly.

Cans and bottles hold their carbonation well when sealed, but heat raises the pressure inside. Store a pack in a hot car in an Indian summer and the first pour will gush, losing gas and aroma in the foam. Keep packaged beer cold and upright.

How to taste carbonation on purpose

Most drinkers notice carbonation only when it is wrong. A little practice makes it a normal part of tasting. Note three things on your next beer: how strong the prickle is when it first hits the tongue, how fine or coarse the bubbles feel and how the beer feels on the tongue after a minute in the glass.

Fine, tight bubbles feel creamy. Coarse, large bubbles feel harsh and gassy. Bottle conditioned beers and well poured draught often have finer bubbles than beer force carbonated in a hurry, though careful force carbonation can be just as good.

Your first step

Pour one beer into two glasses. Drink half of one straight away. Stir the other gently with a clean spoon until most of the fizz is gone, then taste it. Write down how sweetness, bitterness and body changed. It takes five minutes and you will never think of bubbles as decoration again.

Common questions

Why does carbonation make beer taste sharp?

Dissolved CO2 forms a little carbonic acid. Part of the prickle is sensed by the same taste cells that detect sourness, while bursting bubbles add a physical tingle.

How many volumes of CO2 are in beer?

Most lagers and pale ales sit around 2.4 to 2.7 volumes. Cask ales are lower at about 1 to 1.5, while hefeweizen and many Belgian ales reach 3 or more.

Why does flat beer taste sweet?

Carbonation's bite balances sweetness. Remove it and the beer tastes sweeter, softer and heavier. Less aroma reaches your nose as well.