The Chemistry of Great Coffee

Red ripe coffee beans are sorted on a coffee plantation near Poas, Costa Rica in this file photo. (AP Photo/Kent Gilbert)

High-end coffee is suddenly seeping into fast-food restaurants faster than you can ask for fries with that.

McDonald's started offering organic coffee roasted by Green Mountain Coffee Roasters at 650 locations in New England and Albany, New York, this month. Burger King now lets you order coffee brewed one cup at a time, so you avoid that burnt taste.

The fast food chains are acknowledging America's love affair with quality java.

Coffee that's not rot gut is called specialty coffee in the industry, which means a higher grade of bean is used and the roasting and brewing is treated as a "craft."

In 2004, 16 percent of U.S. adults drank specialty coffee daily, according to the Specialty Coffee Association of America. This slice of the market, which involves cafes, kiosks, coffee carts and retail roasters, at a total of 17,400 locations, amounted to $8.96 billion by the end of 2003.

The United States imports and consumes more coffee than any other country.

How it's done

When it comes to great flavor, coffee chemistry boils down to roasting and brewing.

When the inside of the bean reaches about 400 degrees, it begins to turn brown. Oil locked inside the beans begins to emerge. This is when the flavor takes shape. The more oil, the stronger the flavor.

Roasted coffee is a perishable food. The flavor peaks a few days after roasting and fades once the coffee is exposed to air, light or moisture. For this reason, aficionados keep their beans or fresh grounds in an airtight container at room temperature. 

If you're one of the many people who drink coffee for the pick-me-up, you might think an espresso or cappuccino would be most effective. Not necessarily so. Caffeine content goes up as the water spends more time in contact with the grounds. Espresso brewing takes 25 seconds. Other methods take several minutes. Darker roasts also yield more caffeine.

Flavor is the combination of aroma, acidity and body.

Body is the sensation of heft or viscosity, something like oil, on the palate. Longer roasting yields more body. But that also decreases acidity, the tingly taste on your tongue. So there's a trade-off between body and acidity.

Acidity isn't bitterness though. Bitterness comes from skimping on grounds when you brew, brewing for too long, and brewing in a pot or machine with residual grounds left from hours, days or weeks ago.

The Starbucks way

So you want to know how Starbucks does it?

First, they discard opened bags of beans after one week. Second, hot coffee is stored in thermal carafes, not on burners.

Third, they use two tablespoons of ground coffee for each six ounces of water. (The more standard recipe is one to two tablespoons per six ounces of water).

The company roasts at four plants, located in the U.S. and Amsterdam. Roasted coffees are immediately sealed in packages that let carbon dioxide gas out but keep air, light, water, and heat from getting in, Starbucks spokesman Chris Gimbl told LiveScience.

As Starbucks brews on, competition in the specialty coffee realm is expected to increase from outlets once known for the blandness of their coffee. Dunkin' Donuts, on to the idea and offering specialty brews for years, claims to have sold nearly a billion cups of coffee last year, more than any other retailer in the country.

Robin Lloyd

Robin Lloyd was a senior editor at and Live Science from 2007 to 2009. She holds a B.A. degree in sociology from Smith College and a Ph.D. and M.A. degree in sociology from the University of California at Santa Barbara. She is currently a freelance science writer based in New York City and a contributing editor at Scientific American, as well as an adjunct professor at New York University's Science, Health and Environmental Reporting Program.