Humulone is oxidised in conditions which parallel the hops treatment conditions in brewing. A number of products can be isolated from the reaction mixture by counter current distribution. These are oxidation products of isohumulones; this paper is about their preparation, isolation and identification.
A complex mixture of oxidation products is formed from iso-a-acids during wort boiling. These substances are already present in hops and persist to beer. Seven major constituents of such a mixture, obtained from pure humulone, were isolated by countercurrent distribution and their structures were elucidated, mainly by mass spectroscopy. The bitterness of the new beer substances was evaluated against trans isohumulone as a reference standard. These oxidation products of iso-a-acids are not extracted with iso-octane and they therefore escape the usual beer bitterness assay.
During boiling, substantial amounts of hop α‐acids are transformed into oxidation products containing the same cyclopentane nucleus as the iso‐α‐acids: these oxidation products, which have been called abeo‐iso‐α‐acids I, II and III, are separable by countercurrent distribution. Lager beers contained between 88 and 160 mg. of abeo‐iso‐α‐acids per litre. Although the abeo‐iso‐α‐acids are almost devoid of bitterness, they have strong foam‐producing properties.
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