It's not the grains to blame, but our genetics: Researchers have uncovered the reasons behind the bitterness of this popular drink.

The bitterness of coffee manifests differently in various individuals, and researchers from the Leibniz Institute for Food Systems Biology at the Technical University of Munich have made strides in understanding the reasons behind its presence for some people. While caffeine has long been recognized as a bitter compound, it is not the only culprit for coffee's bitterness, as even decaffeinated beverages retain a bitter taste. After years of research, scientists have finally uncovered the true causes of this bitterness, as reported by LSB.

The study's author and PhD candidate at the institute, Colin Bichlmaier, identified a new class of compounds that contribute to bitterness, in addition to the previously known bitter substances formed during the roasting of coffee beans. The focus of the study was on mozambioside—a compound naturally present in Arabica coffee beans that is approximately ten times more bitter than caffeine.

Mozambioside primarily activates two bitter taste receptors—TAS2R43 and TAS2R46. However, it significantly degrades during roasting, prompting researchers to investigate whether its breakdown products contribute to bitterness. Lead researcher Roman Lang explains that seven breakdown products of mozambioside are formed during roasting, with their concentrations varying based on roasting conditions. These compounds nearly completely transfer into brewed coffee.

After conducting cellular tests, the research team confirmed that these breakdown products activate the same bitter taste receptors as mozambioside, with three of them eliciting an even stronger response. However, their concentration in brewed coffee was too low to produce a strong taste on their own. Instead, the combination of mozambioside and its roasting products resulted in most participants perceiving bitterness.

Out of eleven subjects, eight identified the bitter taste, one described it as astringent, and two did not detect any significant flavor. Genetic analysis revealed that sensitivity to bitterness is influenced by individuals' genetic makeup: two individuals had defective copies of the TAS2R43 gene, seven had one defective and one intact copy, and only two possessed both functional copies. These findings help to understand how roasting affects coffee flavor and may pave the way for developing coffee varieties with personalized flavor profiles.

In addition to exploring taste, the study contributed to health science, as bitter taste receptors play a role in various physiological processes beyond taste perception. According to Lang, these receptors are found not only in the mouth but also in other organs, where they may influence metabolism, immune response, and reaction to pathogens. Research into bitter compounds in coffee remains an evolving field. Although scientists have identified several known bitter compounds, such as chlorogenic acids, diketopiperazines, and 4-vinyl catechol oligomers, their exact interactions with taste receptors are still being studied.

The Leibniz Institute continues to investigate these mechanisms, aiming to determine how different compounds interact with the body beyond their role in flavor formation. In another study, researchers seek to understand whether genetic variations in bitter taste receptors can influence not only coffee perception but also dietary choices and health conditions. For example, individuals with heightened sensitivity to bitterness tend to consume fewer bitter vegetables, which may be significant for developing dietary strategies.

This material is for informational purposes only and does not contain advice that may affect your health. If you experience issues, consult a specialist.