The longer you roast coffee, the more you “burn” the coffee and therefore, you can say that you “burn off” more caffeine than a lighter roast. So yes – there is less caffeine in a darker roasted coffee.
Why no also? If you actually measure your coffee by weight, then you’ll basically require more coffee in volume of darker roasts than you do in a lighter roast. For example, at Old Rock store, we use more coffee for a French roast per volume (but same weight) compared to our Vienna roast. The result is that you’ll have more caffeine in with the French roast than you’ll have in the Vienna roast.
So, at home, here is a simple measuring tip when making Vienna versus French: using the Melitta scoop to measure your Vienna roasted coffee, use one scoop per cup where the scoop is full but not heaping – flat on the top. For your French roasted coffee, use one slightly heaping scoop per cup. For Italian roasted coffee, use a full heaping Melitta scoop.
If you don’t have a Melitta scoop at home, come and see us at the store and we’ll provide you with one at no cost.