Light roasted coffee has more caffeine than dark roasted coffee.
Technically, per bean, more of the caffeine is cooked out of the dark roast. However, other things are also roasted out of a dark roast to the point that the individual beans are also lighter and smaller. When brewing coffee, usually you either weigh your dose of beans out, or you use a scoop for some consistency. Either method will result in more dark roast beans ultimately making it into the brew than would with a (larger, heavier) light roast.
Typically, this more than cancels out the reduced caffeine content per bean, so a brew of dark roast coffee still typically has more caffeine in it.
If I remember correctly, dark roast was also originally devised to hide bad-quality coffee beans. Nowadays it is often implied that darker roasts are better, which actually isn't necessarily the case.
Dark roasts have a more consistent taste/flavor and it has a longer shelf life, so it's easier to know what you're getting. If you want to taste the variety of flavors coffee can have, you'll go for fresher lighter roasts.
Yup, I had to explain this to so many people when I sold coffee. Nobody believed me at all. I explained that dark roast had more of the caffeine cooked out of it.
Eh, sorry about that. wefwef told me to retry because there was an error while posting my comment. So I did retry... many times. I was actually sure the comment wasn't posted at all until I saw your reply.
I remember looking this up and the difference is around 1%, so if you're worried about caffeine intake you're better off leaving a mouthful in the bottom of your cup than changing beans.
Thank you for laying it out like this. I'd often heard that about light roasts, but had never noticed any difference in my caffeine response when I switch roasts. At any rate I've always preferred dark for the flavor, but it's good to know I'm not sacrificing any buzz for it!
I've honestly never thought of that. Guess that's why I've not been able to feel a real difference in my morning coffee when I use different roasts. I always thought "well it can't be losing that much caffeine because it doesn't feel any different than my medium or light roasts."