Bitterness

Bitterness is one of the five basic tastes in humans, characterized by a sharp, often astringent or pungent sensation that lingers after the initial contact with taste receptors. It is detected by a family of taste receptors called TAS2Rs located on taste receptor cells in the tongue and other parts of the oral cavity. Humans typically perceive bitterness as aversive as a protective mechanism against ingesting potentially toxic compounds, many of which are plant alkaloids. Sensitivity to bitter compounds varies widely among individuals due to genetic variation in TAS2R genes, as well as age, dietary experience, and cultural exposure. Some people are "supertasters" with heightened bitter perception, while others are relatively insensitive.

Bitterness arises from a diverse set of chemical structures, including alkaloids such as quinine and strychnine, alkaloids like caffeine, terpenoids, and various phenolics. The same bitterness can be experienced in drinks (coffee, tea, tonic water) and foods (dark chocolate, bitter greens) depending on concentration and matrix. Food processing and flavor science often seek to mask bitterness through sweeteners, salt, fat, or savory flavors, and, in pharmaceuticals, bitter taste can hinder medication acceptance; bitter masking and coating strategies are routinely used.

Beyond taste, bitterness is used metaphorically to describe resentment or sourness in mood, often reflecting long-standing negative feelings rather than a transient reaction. In botany and ecology, bitterness may deter herbivory and influence plant–animal interactions.