Researchers Unlock Key to Hops’ Unique Bitter Flavor in Beer

Hops, a vital ingredient in beer brewing, have captured the attention of researchers who have made significant advances in understanding how these plants produce their characteristic flavors. A team led by Prof. Wang Guodong from the Institute of Genetics and Developmental Biology (IGDB) at the Chinese Academy of Sciences has successfully identified the enzyme responsible for synthesizing chiral α-bitter acids, which impart the distinctive bitterness to beer.

Historically, hops have played an essential role in brewing not only for flavor but also as natural preservatives that extend the shelf life of beer. The female flowers of hops contain glandular trichomes that synthesize various metabolites. These include terpenes, which provide aroma, and xanthohumol, known for its antioxidant properties. Until now, the enzyme responsible for the final step in the biosynthetic pathway of α-bitter acids, known as α-bitter acid synthase (α-BAS), had remained unverified for over a decade despite the identification of potential candidate genes.

To tackle this long-standing challenge, the research team developed a highly sensitive liquid chromatography–mass spectrometry (LC–MS) detection method. This innovative technique allowed them to differentiate between the two chiral forms of α-bitter acids: 6S and 6R. Their findings, published in the journal Plant Communications, indicate that hop glandular trichomes primarily accumulate the 6S-type α-bitter acid.

A crucial discovery involved the precursor of α-bitter acid, known as deoxy-α-bitter acid, which undergoes spontaneous oxidation when exposed to air. This reaction leads to the formation of a racemic mixture of both chiral forms, complicating the analysis of α-BAS. By overcoming this technical challenge, the researchers established a yeast heterologous expression system to systematically assess more than ten candidate genes.

Their experiments identified the gene HlMO18 as the specific enzyme that catalyzes the oxidation of deoxy-α-bitter acid to predominantly produce the 6S form. Further mechanistic analyses revealed key amino acid residues essential for the enzyme’s activity, providing deeper insight into its function.

The research also demonstrated that the 6S-type α-bitter acid synthase forms a metabolic complex with upstream enzymes, elucidating why only the 6S form accumulates in hop glandular trichomes. This comprehensive understanding completes the biosynthetic map of α-bitter acids in hops, offering valuable insights for the brewing industry.

Looking ahead, the research team aims to leverage synthetic biology to engineer industrial yeast strains capable of producing “hoppy beer” that captures authentic hop flavors without using hop plants. This innovative approach has the potential to lower production costs and enable the creation of customized, flavor-rich beers, marking a new era for innovation in brewing.

The study, authored by Chengyong Feng and colleagues, represents a significant advancement in the understanding of hop biosynthesis and its implications for the beer industry. For more information, please refer to the publication in Plant Communications (2025).