Study sheds light on why coffee tastes so bitter to some

The study demonstrated for the first time that an individual's genetic tendencies also play a role in determining how bitter roasting substances in coffee taste.

New Delhi: Genetics may be contributing towards how one perceives the taste of coffee -- 'bitter' or 'not bitter', according to a study.

Researchers at the Technical University of Munich, Germany, have identified a new group of bitter compounds in roasted Arabica coffee and analysed how they influence its taste.

They also demonstrated for the first time that an individual's genetic tendencies also play a role in determining how bitter these roasting substances taste. The findings are published in the journal Food Chemistry.

Beans from the 'Coffea Arabica' plant are roasted to develop a flavour before being ground and brewed for a beverage.

While caffeine has been known to be bitter-tasting for a long time, even de-caffeinated coffee tastes bitter, possibly suggesting that there are other substances contributing to the bitter taste of roasted coffee, the researchers said.

'Mozambioside' is one such substance in Arabica beans, known to taste about 10 times more bitter than caffeine and activate two of the roughly 25 bitter taste receptors in the human body -- namely, the 'TAS2R43' and 'TAS2R46' receptors.

However, we found that mozambioside levels significantly drop during roasting, and therefore, the substance "only makes a small contribution to the bitterness of coffee", according to lead researcher Roman Lang.

"This prompted us to test whether roasting produces breakdown products of mozambioside are also bitter and could affect coffee's taste," Lang said.

The team showed that mozambioside degrades into seven different products during roasting, which are found in varying amounts in roasted coffee, depending on roasting temperature and duration.

Through experiments on cells, the seven products were found to activate the same bitter taste receptors as mozambioside.

Three of the roasting products even had a stronger effect on the receptors, compared to the original mozambioside, the researchers said.

However, they also found that the concentrations of these roasting products measured in brewed coffee were too low to induce a noticeable taste on their own.

Only a combination of mozambioside and its roasting products in a sample led eight out of eleven participants to perceive a bitter taste, the team said.

Further, a genetic test showed that taste sensitivity depended on the genetic inclination of the participants -- two had both copies of the TAS2R43 gene variant defective, seven had one intact and one defective variant of the gene, while only two people had both copies of the gene intact.

"The new findings deepen our understanding of how the roasting process influences the flavour of coffee and open up new possibilities for developing coffee varieties with coordinated flavour profiles. They are also an important milestone in flavour research, but also in health research," Lang said.

"Bitter substances and their receptors have further physiological functions in the body, most of which are still unknown," Lang said.

According to Lang, there is still a lot of work to be done, since for many bitter substances in coffee alone, it is not yet known which bitter taste receptors they activate, even though millions of people worldwide drink coffee every day.