What happens to caffeine during the roasting process?

There is a persistent myth in the coffee world that darker roasts have less caffeine because the "caffeine is burned off" during the long roasting process. In reality, caffeine is incredibly resilient to heat. To break down caffeine, you would need temperatures far higher than those reached inside a commercial coffee roaster. During a typical roast profile, the caffeine molecule remains intact from the green stage to the final dark roast. What changes is the physical composition of the bean. During roasting, the bean loses water content and various organic compounds through evaporation and gas emission. This mass loss is what we measure as a percentage of the total weight. Because the bean loses weight but the caffeine content stays the same, the caffeine becomes more concentrated in the remaining mass. If you were to measure by weight (grams of coffee), a dark roast actually contains a higher concentration of caffeine than a light roast. However, the experience of brewing changes these numbers significantly. Most home brewing is done by volume—using a scoop or a tablespoon—rather than by weight. Because darker roasted beans are less dense and more porous than lighter roasts, they take up more space in a scoop. If you use the same volume of coffee, you will actually be using fewer grams of dark roast than light roast, which might result in a slightly lower total caffeine dose in your cup. This highlights why understanding the science behind your coffee is so important. The caffeine content per cup is ultimately dictated by your brewing recipe, your dose (weight of coffee), and your extraction efficiency. While the roast level does influence the flavor profile and the physical density of the bean, it is not a reliable indicator of the caffeine kick you will receive. For those sensitive to caffeine, the best way to control your intake is by using a scale to measure your coffee dose, regardless of whether you prefer a light, medium, or dark roast.