Roasting is a heat process that turns coffee into the fragrant, dark brown beans with which we are most familiar. Before being roasted, the beans were stored green, a state in which they can be kept without loss of quality or taste. Once roasted, however, they should be used as quickly as possible before the fresh roast flavor begins to diminish.
Roasting is a technical skill which approaches an art form. It takes years of training to become an expert roaster with the ability to 'read' the beans and make decisions with split second timing. The difference between perfectly roasted coffee and a ruined batch can be a matter of seconds.
Roasting brings out the aroma and flavor that is locked inside the green coffee beans. A green bean has none of the characteristics of a roasted bean. It is soft and spongy to the bite and smells green, almost 'grassy.' Roasting causes numerous chemical changes to take place as the beans are rapidly brought to very high temperatures. When they reach the peak of perfection, they are quickly cooled to stop the process. Roasted beans smell like coffee, and weigh less because the moisture has been roasted out. They are crunchy to the bite, ready to be ground and brewed.
Most roasters have specialized names for their favored roasts and there is very little industry standardization. This can cause a great deal of confusion for the buyer. But in general, roasts fall into one of four color categories — light, medium, medium-dark, or dark. The perfect roast is a subjective choice that is sometimes determined by national preference or geographic location.
Light brown in color. This roast is generally preferred for milder coffee varieties. There will be no oil on the surface of these beans, because they are not roasted long enough for the oils to break through to the surface
Medium brown in color with a stronger flavor, and a non-oily surface. This roast is often referred to as the American roast because it is generally preferred in the United States.
Rich, dark color with some oil on the surface and with a slight bittersweet aftertaste.
Shiny black beans with an oily surface and a pronounced bitterness. The darker the roast, the less acidity will be found in the coffee beverage. Dark roast coffees run from slightly dark to charred and the names are often used interchangeably which can be very confusing. Be sure to check your beans before you buy them!