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Coffee's bitter secret out
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Saturday, 15 September, 2007, 08 : 00 AM [IST]
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taste perceptions, Scientists have for the first time identified two key compounds that are responsible for the bitter taste of coffee.
A team of German researchers has shown that the bitterness of coffee does not stem from caffeine, but from two compounds that are absent in green raw beans but present in roasted coffee beans.
"Roasting is the key factor the bitter taste in coffee beans. The stronger you roast the coffee, the more harsh it tends to get," said Thomas Hoffman, professor of food chemistry at the Technical University of Munich in Germany. Only 15 per cent of the perceived bitterness is from the caffeine, he said, pointing out that caffeinated and decaffeinated coffee have close levels of bitterness.
The two main classes of compounds responsible for coffee's bitterness are called chlorogenic acid lactones and phenylindanes, the researchers said, presenting the findings at a meeting of the American Chemical Society in Boston, US.
In the past, scientists exploring the makeup of coffee had identified over 25 compounds that could contribute to its bitterness, but the main compounds had remained largely unexplained, the team said.
The studies suggest that prolonged roasting of coffee beans triggerss a sequence of chemical reactions in the beans that lead to the formation of the most intense bitter compounds. The chlorogenic acid lactones are the main source of bitterness in light to medium roast brews, while phenylindanes the breakdown products of these lactones - are found at higher levels in dark, roasted coffee.
These chemicals deliver a more lingering, harsher taste than their precursors that why dark, roasted coffees are usually bitterer explained Hoffman. These findings also throw light on how brewing can influence the taste of coffee.
The scientists believe that the identification of the bitterness compounds may help them develop methods to objectively determine the taste of coffee and to better it through improvement of processing conditions.
"Now that we know how the bitter compounds are formed, we're trying to find ways to reduce them," Hoffman said. Their studies are aimed at developing new methods of processing raw beans.
- Agencies
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