Roasting differences

Medium, Viennese, FrenchDid you know that the lighter the color of the bean is, the more caffeine it typically contains. During the roasting process, heat converts the starch in beans to sugar and then carmelizes them into the brown color that is seen. The acids and caffeine also weaken as heat builds, eventually resulting in the production of the oils that give coffee its aroma and flavor.

The net result of all this is that darker beans give you more aroma and flavor, but less acidity and caffeine. Whereas lighter roasts have a brighter flavor, less bitterness, and more caffeine.