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. Examples of use The addition of a bitterant to ethanol denatures the product. Bitterants are used in antifreeze to prevent pet and child poisonings. It is required by law in some places (France, Oregon, etc.). Gas dusters often use a bitterant to discourage inhalant abuse, although this can cause problems for legitimate users. The bitterant not only leaves a bitter flavor in the air, but also leaves a bitter residue on objects, like screens and keyboards, that may transfer to hands and cause problems (such as when eating). Game cartridges for the Nintendo Switch are coated with denatonium as a safety feature to deter small children from ingesting them. Some button cell batteries manufactured by Duracell are coated with a bitterant to discourage accidental ingestion by children. Examples of bitterants Denatonium is used in a variety of applications as an aversive agent. Sucrose octaacetate Quercetin Brucine Quassin Bitterness scales 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. Brewery 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