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In a discovery that could lead to
better tasting coffee, chemists report finding the compounds that
are most responsible for the brew's bitter taste.
Photo � by
American Chemical Society |
"Roasting is the key factor driving bitter
taste in coffee beans. So the stronger you roast the coffee, the more
harsh it tends to get," Hofmann says, adding that prolonged roasting
triggers a cascade of chemical reactions that lead to the formation of
the most intense bitter compounds.
Using advanced chromatography techniques and a
human sensory panel trained to detect coffee bitterness, Hofmann and
his associates found that coffee bitterness is due to two main classes
of compounds: chlorogenic acid lactones and phenylindanes, both of
which are antioxidants found in roasted coffee beans. The compounds
are not present in green (raw) beans, the researchers note.
"We've known for some time that the chlorogenic
acid lactones are present in coffee, but their role as a source of
bitterness was not known until now," Hofmann says. Ironically, the
lactones as well as the phenylindanes are derived from chlorogenic
acid, which is not itself bitter.
Chlorogenic acid lactones, which include about 10
different chemicals in coffee, are the dominant source of bitterness
in light to medium roast brews. Phenylindanes, which are the chemical
breakdown products of chlorogenic acid lactones, are found at higher
levels in dark roasted coffee, including espresso. These chemicals
exhibit a more lingering, harsh taste than their precursors, which
helps explain why dark-roasted coffees are generally more bitter,
Hofmann says.
The type of brewing method used can also influence
the perception of bitterness. Espresso-type coffee, which is made
using high pressure combined with high temperatures, tends to produce
the highest levels of bitter compounds. While home-brewed coffee and
standard coffee shop brews are relatively similar in their preparation
methods, their perceived bitterness can vary considerably depending on
the roasting degree of the beans, the amount of coffee used, and the
variety of beans used.
Some instant coffees are actually less bitter than
regular coffee, Hofmann says. This is because their method of
preparation, namely pressure extraction, degrades some of the bitter
compounds. In some cases, as much as 30 to 40 percent fewer
chlorogenic acid lactones are produced, leading to a reduced
perception of bitterness, he says.
"Now that we've clarified how the bitter compounds
are formed, we're trying to find ways to reduce them," Hofmann says.
He and his associates are currently exploring ways to specially
process the raw beans after harvesting to reduce their potential for
producing bitterness. They are also experimenting with different bean
varieties in an effort to improve taste. But so far, none of these
approaches - details of which are being kept confidential by the
researchers - is ready for commercialization, he notes.
But the researchers are optimistic that a better
cup of Joe is just around the corner. Perhaps no one could be happier
about the news than Hofmann, who admits that he is an avid
coffee-drinker with a passion for the dark-roasted varieties. |
