Bitterants are commonly used as aversive agents to discourage the inhalation or ingestion of toxic substances.
[7] The taste thresholds of other bitter substances are rated relative to quinine, which is thus given a reference index of 1.
[7][8] For example, Brucine has an index of 11, is thus perceived as intensely more bitter than quinine, and is detected at a much lower solution threshold.
This was discovered in 1958 during research on lignocaine, a local anesthetic, by MacFarlan Smith of Gorgie, Edinburgh, Scotland.
[10] This technique was adopted at the same time as another method based on measuring the concentration (in milligrams per litre; parts per million w/v) of IAA isomerized α acids in a beer, causing some confusion among small-scale brewers.