There are four main types of roast: light, medium, medium dark, and dark.
A common misconception is that the darker the roast the higher the caffeine, perhaps because darker roasts sometimes taste more bitter. But the lighter roasts are actually slightly higher in caffeine as it has not all been pushed out during the process.
Light roasts are generally used for more milder coffee. These beans do not have oil on the surface because they have not been heated long enough for the oils to come out. With light roasting the original flavor of the bean comes through the best. Some lights roasts go by such names as Half-City, Light City, New England, or Cinnamon.
Medium roasts have a stronger flavor and are medium brown; they are still not very oily and are actually a tad sweeter than light roast. Medium roasting usually results in balanced flavor and aroma, and this is the most popular type of roast in America. That’s probably why another name for it is American or sometimes City or Breakfast.
Medium-dark roasts have some oil and a rich dark, almost black, color. They have a slightly bitter after taste but, curiously, the coffee from dark roast is less acidic. The predominant flavor comes from the roasting so original bean flavor is most noticeably gone. These may be labeled as French, Italian, Viennese, Espresso, European, New Orleans, Continental, or High.