The next time you enjoy a carbonated beverage, you can do so with an enhanced understanding of the molecular mechanism that provides its distinctive flavor sensation. Chandrashekar et al. genetically ablated specific sets of taste cells in mice and found that the sensation of CO2 was lost in animals lacking taste cells that sense sour flavors. A screen for genes specifically expressed in these cells revealed the gene encoding carbonic anhydrase 4, which catalyzes hydration of CO2 to form bicarbonate and free protons. Knockout animals not expressing the carbonic anhydrase 4 gene also showed diminished sensation of CO2. The protons produced by the enzyme appear to be the actual molecules sensed by the sour-sensitive cells. This process, combined with tactile sensations, appears to be the source of the popular fizzy sensation.