Humulone: Understanding The Bittering Agent In Hops And Its Aroma

Humulone is a bittering molecule found in hops, a small genus of flowering plants native to the Northern Hemisphere. Hops are used as flavouring and stabilizers during beer brewing, with the female flowers being added to the beer at different stages of the process to impart different flavours and aromas. Humulone is one of three alpha acids found in hops, the other two being ad-humulone and cohumulone. During the brewing process, humulone degrades into isohumulone, which is significantly more soluble than humulone. Isomerization of humulone into isohumulone is what gives beer its characteristic bitter flavour.

Humulone is a bitter molecule found in hops, which are used to flavour and stabilise beer during brewing

Humulone is a member of the alpha acids, which give hopped beer its bitter flavour. Alpha acids are only bitter when boiled, as this process changes them into iso-alpha acids. Humulone, specifically, degrades into cis- and trans-isohumulone. These iso-alpha acids are more soluble than humulone at the pH levels present during the brewing process.

Humulone is a phloroglucinol derivative with three isoprenoid side-chains: two prenyl groups and one isovaleryl group. Its structure means that it is designated as an acid, with ring enol moieties that are in a vinylogous relationship with the ring and side chain carbonyl functional groups.

Humulone is not the only alpha acid found in hops. The other two are cohumulone and adhumulone, and together they make up the alpha acid percentage of the hop. During the boiling process, these three acids isomerise into six iso-alpha acids: trans-isocohumulone, trans-isohumulone, trans-isoadhumulone, cis-isocohumulone, cis-isohumulone, and cis-isoadhumulone.

Hops are added at different stages of the brewing process depending on whether they are considered aroma, bittering, or dual-purpose hops. Aroma hops are low in alpha acids and are added late in the boil, during the whirlpool, or during dry hopping. Bittering hops, on the other hand, are high in alpha acids and are added early in the boil. Dual-purpose hops have high amounts of both alpha acids and essential oils and can be added at any stage of the brewing process.

Humulone is a phloroglucinol derivative with three isoprenoid side-chains

Humulone is a well-known bitter principle of beer, and at least 32 derivatives have been isolated, many of which are formed during fermentation and preservation. During the brewing process, humulone degrades into cis- and trans-isohumulone, which are more soluble than humulone at the typical pH levels of the brewing process. Humulone itself is poorly soluble and not particularly bitter, but it is converted into the bitter-tasting and more soluble isohumulones by an isomerization reaction that occurs during the boiling of the wort.

Humulone is a vinylogous type of organic acid, with the acidity of the ring enol moieties arising from their vinylogous relationship with the ring and side-chain carbonyl functional groups. Its structure includes two prenyl groups and one isovaleryl group as the three isoprenoid side-chains.

Humulone can be synthesized in the laboratory by acylating benzene-1,2,3,5-tetrol with isovaleryl chloride to create 2,3,4,6-tetrahydroxyisovalerophenone, followed by prenylation with 1-bromo-3-methyl-2-butene to produce humulone. Biosynthesis of humulone in Humulus lupulus begins with an isovaleryl-CoA unit and three malonyl-CoA units, catalysed by phlorovalerophenone synthase. This conversion results in the benzenoid 3-methyl-1-(2,4,6-trihydroxyphenyl) butan-1-one. Dimethylallyl pyrophosphate is then obtained from the deoxyxylulose pathway, where prenylation of the benzenoid occurs, ultimately yielding humulone.

Humulone is one of the three alpha acids in hops, which contribute to a beer's bitterness

Humulone is a bitter-tasting chemical compound found in the resin of mature hops (Humulus lupulus). It is a member of the class of compounds known as alpha acids, which give hopped beer its bitter flavour. Humulone is one of three alpha acids in hops, the other two being cohumulone and adhumulone. These three acids are also known as bittering hops, and they are used early in the boil to add bitterness to beer and to stabilise it, increasing its shelf life.

During the brewing process, humulone degrades into cis- and trans-isohumulone, which are significantly more soluble than humulone at the pH levels present in the brewing process. Humulone is a phloroglucinol derivative with three isoprenoid side-chains: two prenyl groups and one isovaleryl group. The ring enol moieties that give rise to its designation as an acid lie in their vinylogous relationship with the ring and side chain carbonyl functional groups.

Humulone is under basic research with in vitro studies to determine if it has biological properties, such as possible GABAA receptor activity or antibacterial effects.

Humulone degrades into cis- and trans-isohumulone during the brewing process

Humulone is a bitter-tasting chemical compound found in the resin of mature hops. It is a member of the class of compounds known as alpha acids, which give hopped beer its characteristic bitter flavour. Humulone is a phloroglucinol derivative with three isoprenoid side-chains. Two side-chains are prenyl groups and one is an isovaleryl group.

During the brewing process, humulone degrades into cis- and trans-isohumulone. These "alpha acids" survive the boiling process, although numerous oxidised derivatives are produced. The iso-alpha acids are significantly more soluble than humulone at the pH levels typically present in the brewing process. The iso-alpha acids are responsible for 70% of the observed sensory bitterness in beers.

Humulone is transformed into isohumulone to elicit a bitter taste in beer. Humulone is a well-known bitter principle of beer, and at least 32 derivatives of humulone have been isolated, many of which are formed during fermentation and preservation.

Humulone is under basic research to determine if it has biological properties, such as possible GABAA receptor activity or antibacterial effects

Humulone is a bitter-tasting chemical compound found in the resin of mature hops. It is a well-known bitter principle of beer and is a major compound in hops. Humulone is under basic research to determine if it has biological properties, such as possible GABAA receptor activity or antibacterial effects.

Humulone is a prenylated phloroglucinol derivative comprising 35–70% of hops alpha acids. It is a positive allosteric modulator of GABAA receptors and displays sedative and hypnotic behaviour. Humulone's GABAA receptor function can be enhanced by ethanol and hops modulators, suggesting a probable enhancement in the intoxicating effects of ethanol in hops-enriched beer.

In addition, humulone exhibits antibacterial properties against Gram-positive bacteria such as Bacillus subtilis and Staphylococcus aureus. It also has a mild antibiotic/bacteriostatic effect against Gram-positive bacteria.

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