Bitterant

A bitterant (or bittering agent) is a chemical that is added to a product to make it smell or taste bitter. Bitterants are commonly used as aversive agents to discourage the inhalation or ingestion of toxic substances.

The threshold for stimulation of bitter taste by quinine averages a concentration of 8 μM (8 micromolar). The taste thresholds of other bitter substances are rated relative to quinine, which is thus given a reference index of 1. 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. The most bitter substance known is the synthetic chemical denatonium, which has an index of 1,000. It is used as an aversive agent (a bitterant) that is added to toxic substances to prevent accidental ingestion. This was discovered in 1958 during research on lignocaine, a local anesthetic, by MacFarlan Smith of Gorgie, Edinburgh, Scotland.

Beer bitterness scales attempt to rate the perceived relative bitterness of beer. The bitterness of beer is provided by compounds such as isohumulones from hops used during brewing.

The International Bittering Units scale, or simply IBU scale, is measured through the use of a spectrophotometer and solvent extraction a calculation is performed on this absorbance to give a result in IBU. 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. The American Society of Brewing Chemists, in the introduction to its methods on measuring bitterness, points out some differences between the results of the two methods:

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