Do darker roasts have more caffeine than lighter roasts?

"I want more caffeine, can I get a darker roast?"

This is a common question, especially first thing in the morning when we're all still working to get our brains to a fully functioning state. Unfortunately, if someone gets an extra boost from a darker roast, it would be almost entirely a placebo effect rather than an actual, meaningful increase in caffeine.

Caffeine is a methylxanthine alkaloid that does not break down (melt) until it reaches 460F. In order to achieve this, one would likely catch their coffee on fire inside the roaster and subsequently turn their coffee to charcoal. So, to answer the question, is there more caffeine in dark roasted coffee vs light roasted coffee? The objective answer is no.

That being said, holding all brew parameters constant except light vs dark roasted coffee, it is possible to get an un-noteworthy amount of additional caffeine in the cup. For example in an 8oz cup of coffee that already has 224mg of caffeine, you could get approximately 17mg of additional caffeine using a darker roast vs a lighter roast. That's a 7.5% boost in caffeine or the equivalent of drinking an extra 0.6 oz of the same coffee.

This slight increase in caffeine is due primarily to two things: First, dark roasted coffee is less dense than light roasts. So let's pretend that you get 50 beans after weighing out 10 grams of dark roasted coffee, then you weigh out 10 grams of light roasted coffee but only get 46 beans because it's denser. Remember, the darker roasted and lighter roasted coffee has the same amount of caffeine per bean because it has not broken down but you have a slightly higher caffeine content per serving in the darker roasted coffee recipe simply because there are more beans present. Second, because darker roasted coffees are more porous than light roasted coffees, holding all else constant, you should expect to get a higher extraction of all compounds present including caffeine. Obviously, this can be adjusted by small changes to your brewing recipe.

Conclusion:

1. Darker roasted coffee does not objectively have more caffeine than light roasted coffee.
2. A darker roasted coffee may deliver an un-noteworthy amount of caffeine into the cup because there are a few more beans present due to less density.
3. The easiest way for you to truly get extra caffeine is by getting extra espresso or additional brewed coffee.

1. https://medium.com/@hanjuliet/correlation-between-caffeine-and-roast-levels-using-hplc-833c5d57b12b 

2. https://pubchem.ncbi.nlm.nih.gov/compound/Caffeine