Researchers at the Leibniz Institute for Food Systems Biology at the Technical University of Munich have identified a new group of bitter compounds in roasted Arabica coffee, bringing them closer to understanding why bitterness varies among individuals. Their study, published in Nature Communications, also reveals that genetic predisposition plays a key role in how people perceive coffee’s bitter taste.
Beyond Caffeine: The Hidden Contributors to Coffee’s Bitterness
While caffeine is widely recognized as a bitter compound, even decaffeinated tastes distinctly. This suggests that other substances formed during roasting contribute to the overall flavor profile.
Doctoral researcher Coline Bichlmaier investigated one such compound: mozambioside, a bitter-tasting substance found in Arabica beans. Mozambioside is approximately ten times more bitter than caffeine and activates two 25 known bitter taste receptors in humans—TAS2R43 and TAS2R46. However, roasting significantly reduces mozambioside levels, prompting researchers to explore whether its breakdown products also contribute to bitterness.
The study found that roasting produces at least seven degradation products of mozambioside, varying concentrations depending on roasting temperature and duration. These compounds are transferred almost entirely into brewed coffee, leading researchers to examine their effects on taste perception.
Genetics and the Perception of Bitterness
The team conducted a sensory study with eleven participants to determine how these roasting compounds influence taste. When tested individually, the concentrations of these roasting compounds in brewed coffee were too low to elicit an intense bitter sensation. However, when combined with mozambioside, eight participants reported a distinctly bitter taste; one described it as astringent, and two perceived no particular taste.
Genetic analysis revealed why taste perception differed: variations in the TAS2R43 gene influenced bitterness sensitivity. Two participants had defective copies of the gene, making them less sensitive to the bitter compounds. Seven had one functional and one faulty gene variant, while only two had both copies intact, making them highly responsive to coffee’s bitterness.
Implications for Coffee and Health Research
These findings deepen the understanding of how roasting influences coffee’s flavor and could help develop coffee varieties with tailored taste profiles. According to lead researcher Roman Lang, the study is an essential milestone in broader flavor and health research.
“Bitter substances and their receptors have further physiological functions in the body, most of which remain unknown,” Lang explained. Beyond taste, bitter receptors are found in other organs, including the respiratory tract, intestines, and blood cells, where they may play roles in pathogen defense, metabolism regulation, and other physiological processes.
With millions of people consuming coffee daily, researchers believe there is still much to learn about the interactions between bitter compounds and human biology. Future studies may explore how different bitter substances activate taste receptors and how these receptors influence overall health.
Reference: Coline Bichlmaier, Sonja Maria Fröhlich, Valeria Brychcy, Angelika Graßl, Maik Behrens, Roman Lang. Contribution of mozambioside roasting products to coffee’s bitter taste. Food Chemistry, 2025.
