When Marash Girl's daughter and friend sat down to coffee at the breakfast table in Marash Girl's kitchen this morning, a conversation on the caffeine content of coffee ensued. "Did you know that dark roast coffee has less caffeine than light roast?" No, Marash Girl did not know, although Marash Boy swore that when he drinks a lighter roast, he feels more "caffeinated"! Marash Girl was in a quandary as to how to respond, since she loves dark roast, but decaffeinated dark roast, so that can't be counted in the discussion!
A bit of research was required and this is what Marash Girl discovered. All things being equal (i.e., the same size bean, the same type bean), when roasted longer, the roasted coffee bean loses not only caffeine, but mass, the darker the roast, the less caffeine and the less massive the bean. The argument goes that if coffee is being brewed at home using a measuring scoop, then the ground dark roasted coffee is likely to have less caffeine than the similarly ground light roasted coffee. But if the coffee is being brewed by weight, then the resulting brewed dark roasted coffee will have more caffeine than the brewed light roasted coffee. But this argument makes no sense to Marash Girl. If there is less mass to the dark roasted bean, then it would take a greater number of beans to be ground into a measuring scoop than the light roasted beans. Same with measuring by weight. Given that equation, it seems that the caffeine content would be the same. Or perhaps folks measure out less coffee when they're using dark roast than they do when they're using light roast! The way Marash Girl figures it, dark roast has less caffeine than light roast, NOT cup for cup, NOT measure for measure, NOT weight for weight, but roasted bean for roasted bean!