Coffee lovers who want to avoid a bitter cup of morning brew should stay away from darker roasts, according to scientists who claim to have isolated the chemical compounds responsible for harsh-tasting java.
Caffeine, often blamed for coffee's perceived bitterness, is less at fault than other compounds in the cup, according to the study, presented Tuesday at an American Chemical Society meeting in Boston. The culprits include chlorogenic acid lactones and phenylindanes, compounds only found in roasted beans, not in green or raw coffee beans.
"Roasting is the key factor driving bitter taste in coffee beans," said the lead study author, Thomas Hofmann, a professor of food chemistry and molecular sensory science at Technical University of Munich, in a statement. "The stronger you roast the coffee, the more harsh it tends to get."
Chlorogenic acid lactones, comprising about 10 different chemicals in coffee, are more present in lighter roasts, while phenylindanes, the result of the breakdown of chlorogenic acid lactones, appear in darker roasts. The phenylindanes have more of a "lingering, harsh taste," according to the study.
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Roasting is considered an art by many coffee companies. The National Coffee Association of U.S.A. Inc. lists 16 different roasts levels on its Web site, from "light city" to "French." The longer the beans are heated, the darker the color and the more oils on the surface of the beans.
Starbucks Corp., the world's largest chain of coffee shops, typically heats its beans to the so-called second pop, when "the full flavor potential begins to develop in the beans, bringing all of their attributes into balance," according to its Web site.
George Howell is a proponent of the lighter-is-better school of thought. His company, Terroir Coffee Co., based 20 miles outside of Boston, is known for roasting beans just beyond the first pop, a stage he calls full flavor roast.
"You want to roast as light as possible," Howell said in an interview last month. "Certain flavor components and aromatics that are easily burned off in roasting."
As Howell describes it on his Web site, green coffee beans first dry up in the initial stage of roasting, then, as water molecules evaporate, begin to cook from within. The first pop is when the surface of the bean cracks and oils start to spread onto the surface.
The science of roasting has evolved from early colonial days in the U.S., when most individuals bought green beans from a local grocer and burned them in a pan in their hearth, to modern day computerized machines that use "roast profiles" to heat beans to a preset level. Still, some companies prefer a manual approach to roasting, saying skilled workers can better detect when beans are ready than can a machine.
Peet's Coffee & Tea Inc., a publicly traded cafÈ chain based in San Francisco with more than 150 locations, considers the roaster job one of the more important positions at the company.
"It's all about roaster — it's a fairly prestigious job," said James Grimes, Peet's vice president of operations, in an interview in March. "It takes a year before you can roast on your own."
