Researchers Unlock How Hops Create Beer’s Unique Bitterness

Hops are a crucial ingredient in beer brewing, significantly impacting both flavor and economic value. Researchers from the Chinese Academy of Sciences, led by Prof. Wang Guodong, have made a significant breakthrough in understanding the production of α-bitter acids, which provide beer with its characteristic bitterness. Their findings, published in Plant Communications, clarify the long-standing mystery surrounding the enzyme responsible for the final step in the biosynthesis of these acids.

The female flowers of hops are covered in glandular trichomes that synthesize various metabolites essential for defining beer’s flavor and quality. Terpenes contribute to the aroma, while xanthohumol offers antioxidant properties beneficial to human health. Historically, α-bitter acids also acted as natural preservatives, enhancing the shelf life of beer long before modern brewing methods were developed.

Despite having identified several potential genes linked to α-bitter acid production, the specific enzyme α-bitter acid synthase (α-BAS) remained unverified for over a decade. The research team developed a highly sensitive liquid chromatography–mass spectrometry (LC–MS) method to differentiate between the two chiral forms of α-bitter acids—6S and 6R. Their analysis revealed a predominance of the 6S-type α-bitter acid within hop glandular trichomes.

In their investigation, the researchers found that the precursor of α-bitter acid, known as deoxy-α-bitter acid, undergoes spontaneous oxidation in the presence of air. This process results in a racemic mixture of both 6S and 6R types, complicating the verification of α-BAS’s function. By overcoming these technical hurdles, the team established a yeast heterologous expression system and systematically tested over ten candidate genes.

The results identified HlMO18 as the enzyme that specifically catalyzes the oxidation of deoxy-α-bitter acid, leading to the predominant formation of the 6S form. The study also pinpointed critical amino acid residues vital for the enzyme’s functionality. Moreover, mechanistic analyses indicated that 6S-type α-bitter acid synthase forms a metabolic complex with upstream enzymes, which explains the accumulation of only the 6S form in the glandular trichomes.

This research not only completes the biosynthetic map of α-bitter acids in hops but also enhances understanding of the three major flavor compounds in hops. Following this achievement, the researchers aim to utilize synthetic biology techniques to engineer industrial yeast strains capable of producing “hoppy beer.” This innovative approach could yield beers with authentic hop flavors without the need for traditional hop plants, potentially reducing production costs and enabling customized, flavor-rich beverages.

The implications of this research extend beyond academia, offering valuable insights for the brewing industry. As the team continues to explore synthetic biology applications, the future may hold exciting developments for beer production, catering to both traditional tastes and modern preferences.

For further details, refer to the research conducted by Chengyong Feng and colleagues, published in Plant Communications in 2025 (DOI: 10.1016/j.xplc.2025.101528).