Although there are literally thousands of different types, flavors and brands of coffee, all coffee comes from two species of coffee trees. The beans used to make the brew are actually seeds that are found inside the berries. When the beans are removed from the berries they are green and are not ready for making coffee. Roasting is required to bring out the flavor and prepare the coffee for brewing.
When the beans are roasted, the chemical properties of the green coffee beans change. The roasting also gives coffee its particular taste, and the type of roasting can significantly change the final taste of the brew. As beans are roasted they change from green, then to yellow, tan and finally darker and darker brown. In addition, as the bean is roasted, oil begins to gather on the surface giving coffee the aroma that coffee drinkers know so well.
Roasting is important to a cup of coffee's final flavor. Premium Arabica beans such as Jamaican Blue Mountain and Kona are usually only lightly roasted to preserve as much of the original flavor as possible. More "generic" coffee beans, including most Robusta beans are roasted longer, influencing the coffee's flavor more from the roasting process than the actual beans.
The terms "Light Roast" and "Dark Roast" refer to how long the coffee has been roasted. Light roast coffees contain more subtle flavors and tend to be more acidic. Roasting breaks down caffeine, so contrary to what many people believe, dark roasts have less caffeine than light roasts. Each type of roast has its own name amongst coffee connoisseurs. City roast is the lightest roast, American roast is medium and the darkest roasts are called Dark roast. There are many other names and variations of the different roasts, but they are all on the same spectrum of coffee roasting from light to dark.
