Does caffeine content vary by roast degree?

The persistent belief that dark roasts contain less caffeine than light roasts is a classic case of confusing volume with mass. During the roasting process, coffee beans lose moisture and organic matter, causing them to expand and become less dense. If you measure your coffee by the scoop (volume), a dark roast will have fewer beans—and therefore less caffeine—than a light roast. However, if you measure by weight (the industry standard for quality), the caffeine content remains remarkably consistent across the roast spectrum. Caffeine is a thermally stable molecule; it does not 'burn off' or evaporate at standard roasting temperatures. While some academic studies suggest minor thermal degradation occurs during very long, high-temperature roasting cycles, these losses are negligible compared to the impact of brewing variables like grind size and extraction yield. For the producer, this means the caffeine potential of a harvest is largely determined by the coffee species (Arabica vs. Robusta) and the agronomic conditions of the farm, rather than the roaster's profile. The misconception persists because consumers often equate the 'strength' or bitterness of a dark roast with higher caffeine, when in reality, those sensory attributes are products of Maillard reactions and caramelization, not stimulant concentration.