Does Darker Roast Coffee Have More Caffeine?

Yes and No, but mostly No.

Yes - because specialty coffee uses weight to measure the dose for brewing and the density of darker roasts can be significantly lower than light roast coffee. This means that for every gram of coffee weighed, darker roast coffee will have more coffee beans than light roast coffee, therefore more caffeine (slightly, but still more) in total.

Also, as coffee is roasted darker, the coffee bean expands and becomes more porous. This results in larger channels throughout the bean which allows more water to access the caffeine inside the ground coffee during the brewing process. This can result in more caffeine being extracted in darker roasted coffee.

No - because as coffee is roasted, a very small amount of caffeine is destroyed by heat. Even though this amount is very little, it does mean that lighter roast will retain more of the caffeine than dark roast coffee.

But mostly NO - The difference in caffeine content mentioned above are very very minute. When weighing coffee, the difference between dark and light roast will only be a bean or two for every 100 grams of coffee. Generally, 20g or less of coffee is used to produce a cup of coffee (brew or espresso-based), the difference is negligible.

Extraction, not only of caffeine but other flavor components, are affected by many brewing factors such as water temperature, turbulence, and time, as well as, the grind size used. These factors will have as much or even more influence on how much is extracted from the coffee bean into our brewed coffee than how dark the roast is.

Finally, the amount of caffeine lost through the roasting is almost insignificant between light and dark roasts. Actually, the amount of caffeine as a percentage of the composition of the coffee bean will increase slightly as other components such as moisture and acids will rapidly decrease during the roasting process from light to dark roast.

In conclusion, it is a myth that darker roast coffee has more caffeine than lighter roast coffee. One of the main reasons beyond this myth is the misunderstanding that caffeine is the main or even the only attribute of the coffee that produces the bitterness perceived in brewed coffee. Since darker roast coffee generally has more bitterness than lighter roast coffee, it is assumed that the dark roast must have more caffeine. This is an incorrect assumption as there are over 20 compounds in coffee that contributes to the bitterness in coffee; caffeine is just one of the 20 plus compounds!