Changes

The ketones ketone beta-damascenone (rhubarb, red fruits, stewed apples; threshold of 25 ppb <ref name="hall_mitchell" />) can be formed from the oxidation of hop oils, as well as 3-methyl-butan-2-one and 4-methylpentan-2-one. Beta-damascenone has also been found in aged unhopped beers. It was found to increase greatly in aged beer that was at a pH of 3 or 4.2 versus a higher pH. This was attributed to the acidic hydrolysis of glycosides. The release of flavor compounds from glycosides could be present in acidic beers that are aged on fruit or herbs <ref>[https://pubs.acs.org/doi/full/10.1021/jf020085i Investigation of the β-Damascenone Level in Fresh and Aged Commercial Beers. Fabienne Chevance, Christine Guyot-Declerck, Jérôme Dupont, and Sonia Collin. 2002. DOI: 10.1021/jf020085i.]</ref><ref name="Vanderhaegen_2006" />. See [[Glycosides#Acidic_Hydrolysis|Glycosides]] for more information on acidic hydrolysis of glycosides. Damascenone is also found in grapes and is a major flavor component of bourbon <ref name="hall_mitchell" />.