sour

Sour is one of the five basic tastes, alongside sweet, salty, bitter, and umami. It is primarily produced by acids and is characteristic of tastes like lemon juice. The sensation of sourness is detected by taste receptor cells located in taste buds, primarily on the tongue, palate, and throat.12

The hydrogen ions ([H+]) in acids are largely responsible for the sour taste. However, the concentration of hydrogen ions alone doesn't fully determine sourness; the rest of the acid molecule can also affect how efficiently these ions stimulate the taste receptors. Organic acids, like acetic acid in vinegar, can taste more sour than predicted by their hydrogen ion concentration alone. Sourness can also be associated with fermentation, a turned or acidic smell or taste, and in some cases, decay.21