Tasting the Bubbles

It used to be assumed that the tingling sensation of carbonated beverages was due to stimulation of mechanoreceptors by bursting bubbles of CO2. In fact, researchers now know that we also have chemoreceptors for CO2, and that they are located on the same taste cells that detect sour taste. The receptor molecule is the enzyme carbonic anhydrase, which converts CO2 (plus a water molecule) into bicarbonate and a proton. Protons activate the taste cell, which in turn activates the sensory neuron that synapses with it.

Why don’t carbonated beverages taste sour, given that the carbonic anhydrase is located on the sour-detecting taste cells? No one knows for sure, but researchers speculate that the brain interprets CO2 receptor activation plus mechanoreceptor stimulation as primarily a tingling sensation.