The Roasting Process

• Exposing green coffee beans to high temperatures has several effects. Not only does it dry out the beans, rendering them crunchy and ready to be ground, but it also causes a series of chemical reactions within the bean that alter its flavor and caffeine content. As the roasting process continues, the beans reach a higher and higher internal temperature. The higher the internal temperature, the darker the appearance of the bean.

Medium Roasts

• Medium-roasted coffee has a light- to medium-brown color. Medium-roasted beans undergo "first crack" -- when the heated bean expands and cracks its outer covering -- at just over 400 degrees Fahrenheit. Coffee removed from heat between the first and second crack is a medium roast; this coffee retains some of its distinctive "origin flavor," but with an additional smoky roasted taste caused by the heat. Medium roasts removed from heat later in the process have a darker appearance and are sometimes called "medium-dark" roasts. Medium roasts may also be called "city," "American" or "breakfast" roasts.

Dark Roasts

• Some time after first crack, when the internal temperature of the coffee beans reaches 445 to 450 degrees F, it undergoes second crack -- another crack caused by expansion of the bean. By this time, the beans have acquired a dark color, and the roasting has forced oils to the surface of the beans, giving them a slightly shiny appearance. Dark roasts, also called "European," "Italian" or "French" roasts, have a powerful bitter flavor without much acidity. Very little of the original flavor -- the distinctive characteristics created by the coffee's region and cultivar -- are preserved.

Choosing a Roast

• According to the Coffee Roasting Association, the coffee most Americans drink at home is medium roast, which has a moderate caffeine level and a relatively mild, complex flavor. By contrast, darker roasts -- which have slightly lower levels of caffeine -- are typical of European cafes and more intensely bitter. Dark roasts are used for espresso and drinks that use espresso, such as lattes, and are sometimes simply called "espresso" roasts. Even within categories, there are wide variations in flavor and caffeine content, so that some medium roasts may be as bitter as a dark roast. In the end, personal preference is the only guide, and many will find that they enjoy both medium and dark roasts.