Bitter is one of the five basic tastes. Many people find bitter tastes unpleasant; many alkaloids taste bitter, and evolutionary biologists have suggested that a distaste for bitter things evolved to enable people to avoid poisoning.

The bitterest substance known is the synthetic chemical Bitrex [1] http://www.bitrex.com/home.htm (a trademark of UK company Macfarlan Smith) or denatonium benzoate, discovered in 1958. It is a white, odourless solid used as an aversive agent, i.e. an additive that prevents accidental ingestion of a toxic substance by humans, particularly children, and by animals.

The substance phenylthiocarbamide tastes very bitter to most people, but is virtually tasteless to others. This genetic variation in the ability to taste a substance has been a source of great interest to the biological community.

Basic tastes Bitter - Salty - Sour - Sweet - Umami