The tricky word here is stronger. Many people have a preference between dark roast and medium roast coffees, but many people also associate darkness with “strength” and strength with caffeine content. However, this is not the case.
The darker the bean, the lower the caffeine. So there is actually an inverse relationship between darkness and caffeine content. Dark-roast coffees may taste “strong” but they will not keep you awake for that cram session as well as a medium-roast coffee.
The reason behind this difference is dark-roast coffees are roasted longer and to a higher temperature in order to cook the beans to a bolder, darker taste. In the process, some caffeine molecules are physically burned out of the bean, becoming smoke.
If you come by Blanchard's coffee shop seeking a little (or a lot) more caffeine in your cup, follow this simple advice: Drop some espresso in it! That is, Make a Red Eye (coffee+one or more espresso shots)!
Article above written by "The Man, The Myth, The Legend - Jonathan Lesko".