My wife heard at Starbucks the other day that darker coffee has less caffeine because "caffeine burns off during roasting", but I was certain this is not true from my personal experience. I was researching some this morning and came across many roasters confirming that caffeine does NOT burn off during roasting. This page was most informative...
Let’s dispel the most common myth right off the bat: A dark-roast bean contains more caffeine than a light-roast bean due to its stronger flavor. Not true. Actually, the caffeine content in both is virtually the same. An opposing view held by many is that the darker the roast level, the lower a bean’s caffeine since much of it is lost or "burned off" during roasting. Yet caffeine changes very little during a roast. Any significant variation would require a roasting temperature above 600°F. Since temperatures rarely exceed 470°F, a bean’s caffeine remains relatively static across all roast levels.
How does one control the amount of caffeine in a cup of coffee?
As an amateur roaster, I learned to blend the coffee beans with a bean with higher caffeine content, such as robusta. Most coffee (or all?) is Arabica which has less caffeine than Robusta beans. When I roast a batch for my "morning blend" coffee, I will toss in some Robusta beans for the extra kick.