Isohumulone Explained

Isohumulones are chemical compounds that contribute to the bitter taste of beer and are in the class of compounds known as iso-alpha acids. They are found in hops.

Beer

The bitterness of beer is measured according to the International Bitterness Units scale, with one IBU corresponding to one part-per-million of isohumulone. When beer is exposed to light, these compounds can decompose in a reaction catalyzed by riboflavin to generate free-radical species by the homolytic cleavage of the exocyclic carbon-carbon bond. The cleaved acyl side-chain radical then decomposes further, expelling carbon monoxide and generating 1,1-dimethylallyl radical. This radical can finally react with sulfur-containing amino acids, such as cysteine, to create 3-methylbut-2-ene-1-thiol, a thiol which causes beer to develop a "skunky" flavor.^[1]

Formation

Isohumulones are generated by the isomerization of humulone.^{[2] [3]}

See also

• Beer chemistry

Notes and References

1. Web site: UNC chemists figure out what causes 'skunky beer'. eurekalert.org.
2. 10.1016/j.tifs.2005.11.012 . A better control of beer properties by predicting acidity of hop iso-α-acids . 2006 . Blanco . Carlos A. . Rojas . Antonio . Caballero . Pedro A. . Ronda . Felicidad . Gomez . Manuel . Caballero . Isabel . Trends in Food Science & Technology . 17 . 7 . 373.
3. Esslinger, H. M. and Narziss, L. 2003. “Beer.” in Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH Verlag GmbH & Co. KGaA, 2009