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Hops
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Other compounds have been associated with the oxidation of beta acids and are extracted during wort boiling. These are described as giving a long-lasting, lingering bitterness on the palate. They include hydroxytricyclo-lupulone, dehydrotricyklolupulone, and hydroperoxytricyklolupulone <ref>[http://www.sciencedirect.com/science/article/pii/S0308814609001770 Structure determination and sensory evaluation of novel bitter compounds formed from β-acids of hop (Humulus lupulus L.) upon wort boiling. Gesa Haseleu, Daniel Intelmann, Thomas Hofmann. 2009.]</ref>.
The overall affect of oxidized compounds in aged hops has been shown by Val Peacock, former scientist at Anheuser-Busch. Peacock stored hops at four different temperatures for 18 months. His data showed that although the alpha acid content in the hops and the iso-alpha acid content in the beers brewed with them decreased over time, the measured IBU of the different beers was about the same. This is because the oxidized acids in hops show up in the same spectrum as iso-alpha acids when using the ASBC method of measuing IBUs with a spectrophotometer <ref name="Aron">[https://www.homebrewersassociation.org/how-to-brew/resources/conference-seminars Dr. Patricia Aron. "Bitterness and the IBU: What’s It All About?" HomebrewCon 2017 Presentation. ~34 mins in. Retrieved 09/05/2017.]</ref>. This data is shown below:
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