Why Does Sparkling Water Sting the Tongue?

The mild sting of sparkling water is often explained as bubbles bursting against the tongue. Bubbles do provide touch, but experiments have found that people still experience the characteristic carbonation bite when pressure keeps carbon dioxide dissolved and prevents visible bubbles from forming. The main source of the sting is therefore not mechanical impact.

Dissolved carbon dioxide is the key. In the mouth, carbonic anhydrase rapidly helps convert carbon dioxide and water into carbonic-acid-related changes. This activates taste cells involved in sensing acidity. Carbon dioxide and the acidic environment also stimulate trigeminal pathways in the mouth, producing a chemical sensation closer to mild pungency or prickling. Sparkling water is therefore not merely water with moving gas; it also produces acidity and chemical irritation.

Researchers compared carbonated liquid under conditions that either allowed or suppressed bubbles and found similar ratings of bite. Another experiment showed that added air bubbles did not create the bite by themselves, although their tactile stimulation could strengthen an existing carbonation sensation. The central point is that chemical stimulation provides the base, while bubble touch adds to it.

After a bottle is opened, pressure falls and carbon dioxide gradually escapes. Sparkling water left standing loses both bubbles and dissolved carbon dioxide, so its sting and acidity fade together.

https://pmc.ncbi.nlm.nih.gov/articles/PMC3654389/
https://pmc.ncbi.nlm.nih.gov/articles/PMC3749224/