What affects coffee’s bitterness more: roasting techniques or your predisposed genetics? (Photo by Mix and Match Studio on Shutterstock)
Our genetic differences determine coffee flavor preferences
In a nutshell
- Scientists discovered that a common coffee compound called mozambioside breaks down into seven different bitter substances during roasting, each contributing uniquely to coffee’s bitter taste
- About 20% of Europeans have a genetic deletion affecting their bitter taste receptor (TAS2R43), which significantly impacts how intensely they perceive coffee’s bitterness
- These bitter taste receptors aren’t just in our mouths. They’re found throughout the body and may play important roles in our immune system and metabolism, making this research valuable beyond just understanding coffee preferences
FREISING, Germany — Next time you take a sip of coffee and scrunch your nose at its bitter taste, your DNA might be to blame. New research from scientists in Germany has uncovered fascinating insights into why Arabica coffee’s signature bitterness varies from person to person, and it’s not just about how dark the roast is.
The study, published in Food Chemistry, was conducted at the Technical University of Munich’s Leibniz Institute for Food Systems Biology. Researchers have identified a new group of bitter compounds formed during coffee roasting.
“Indeed, previous studies have identified various compound classes that contribute to bitterness. During my doctoral thesis, I have now identified and thoroughly analyzed another class of previously unknown roasting substances,” says study author Coline Bichlmaier, a doctoral student, in a statement.
While caffeine has long been known as coffee’s primary bitter component, even decaffeinated coffee tastes bitter, indicating other compounds are at work. At the heart of this bitter business is a compound called mozambioside, found naturally in raw coffee beans. It’s about ten times more bitter than caffeine and particularly abundant in naturally caffeine-free coffee varieties. However, this may not be at the root of that bitter taste.
“Our investigations showed that the concentration of mozambioside decreases significantly during roasting so that it only makes a small contribution to the bitterness of coffee,” says principal investigator Roman Lang.
Through detailed chemical analysis, researchers tracked mozambioside as coffee beans roasted. They found it breaks down into seven specific compounds, each contributing its own bitter properties. Using ultra-high-performance liquid chromatography and mass spectrometry, essentially very precise chemical detection methods, they measured exactly how much of each compound forms during roasting and transfers into your cup.
When studying Colombian Arabica coffee specifically, they found that not everyone experiences these bitter compounds the same way. A specific gene called TAS2R43, which codes for one of our approximately 25 bitter taste receptors, plays a crucial role. About 20% of Europeans have a deletion in this gene, meaning they’re missing that particular bitter taste receptor entirely.
In standardized taste tests with 11 volunteers, researchers analyzed each participant’s DNA using saliva samples to determine their TAS2R43 gene status. Their genetic test revealed that two participants had both copies of the TAS2R43 gene variant defective, seven had one intact and one defective variant, and only two people had both copies fully intact.
The results revealed striking differences in bitter perception based on genetics. When combining mozambioside with its roasting products in a sample, eight out of eleven test subjects perceived a bitter taste, one found it astringent, and two didn’t notice any particular taste.
During roasting experiments at different temperatures, researchers discovered that some bitter compounds peaked at 240°C, while others continued increasing up to 260°C. These findings join our existing knowledge about other bitter-tasting substances formed during roasting, including compounds called caffeoylquinides (from chlorogenic acids), diketopiperazines (from coffee proteins), and oligomers of 4-vinylcatechols (from caffeic acids).
Bitter taste receptors aren’t only found in our mouths. They exist throughout the body in various organs and tissues. Studies indicate they help fight pathogens in our respiratory tract, assist with defense mechanisms in our intestines and blood cells, and may play a role in metabolism regulation.
“The new findings deepen our understanding of how the roasting process influences the flavor of coffee and open up new possibilities for developing coffee varieties with coordinated flavor profiles,” says Lang. “They are also an important milestone in flavor research, but also in health research. Bitter substances and their receptors have further physiological functions in the body, most of which are still unknown.”
With global production reaching 102.2 million 60-kilo bags of Arabica coffee in 2023/24, understanding these bitter compounds and their perception is major. For coffee lovers and producers alike, this research provides scientific validation for something many have long suspected: we really do experience coffee differently from one another, and it’s written in our genes.
Paper Summary
Methodology
Researchers used several complementary approaches to study coffee’s bitter compounds. Through ultra-high-performance liquid chromatography and mass spectrometry, they identified and measured compounds in both Colombian Arabica coffee beans and brewed coffee. They conducted roasting experiments at temperatures between 200-260°C over various time periods to track compound formation. For taste testing, they recruited 11 volunteers, collected DNA samples via saliva using ORAGENE-DNA collection tubes, and conducted standardized 3-Alternative Forced Choice tests where participants had to identify bitter tastes among control samples. The team also analyzed how these compounds transferred into brewed coffee using multiple preparation methods: filter coffee, Turkish coffee, French press, cold brew, and espresso.
Results
The study found that mozambioside breaks down into seven different compounds during roasting, with concentrations ranging from 21.0 to 170.4 nanomoles per gram in coffee powders. Between 41-128% of these compounds were extracted into brewed coffee. People with functioning TAS2R43 genes could detect bitterness at much lower concentrations than those without the gene. When combining mozambioside with its roasting products at coffee-relevant concentrations, 8 out of 11 participants detected bitterness, even though individual compound concentrations were below their taste thresholds. Two participants with defective TAS2R43 genes showed notably reduced sensitivity to these bitter compounds.
Limitations
The taste test sample size was relatively small at just 11 participants, all recruited from the Leibniz Institute. The study focused primarily on Arabica coffee from Colombia, so results might vary with different coffee varieties or growing regions. The research concentrated on mozambioside and its derivatives, while coffee contains many other bitter compounds that weren’t examined. Additionally, only European genetic variants were considered in the study, limiting its global applicability.
Discussion and Takeaways
This research provides the first detailed look at how mozambioside transforms during coffee roasting and how its bitter products contribute to coffee taste. It demonstrates that genetic variations significantly influence how people perceive coffee’s bitterness. The findings could help coffee roasters optimize their processes for different consumer preferences. Beyond coffee, the research has implications for understanding bitter taste receptors throughout the body and their potential roles in health and disease.
Funding and Disclosures
This research was conducted at the Leibniz Institute for Food Systems Biology at the Technical University of Munich, which is a member of the Leibniz Association. The Leibniz Association connects 96 independent research institutions and is funded jointly by Germany’s central and regional governments. The authors declared no competing financial interests or personal relationships that could influence the work.
Publication Information
Published in Food Chemistry (Volume 469, January 2025). Title: “Contribution of mozambioside roasting products to coffee’s bitter taste” by Coline Bichlmaier, Sonja Maria Frohlich, Valeria Brychcy, Angelika Graßl, Maik Behrens, and Roman Lang. The study builds on previous work by these researchers published in the same journal examining mozambioside roasting products and bitter taste receptor activation.
