The Science Behind Caffeine Content

I’ve heard the question a number of times recently, “Which has more caffeine, dark or light roast? I’ve heard light.” Yet common sense seems to lean toward dark coffees having more caffeine. Who’s right?

The answer? Neither is correct. Or both. It depends.

Let me throw some facts at you.

1. Caffeine is very stable throughout the roasting process. So bean for bean with a light roast vs a dark roast of the same coffee, the beans will each have a very similar percentage of caffeine.
2. Beans expand during the roasting process as cell walls break, moisture (around 90% of their water content) escapes, and the bean hardens. Darker beans (roasted longer) are less dense, or lighter.

So what do we have? All of those beans will have pretty much the same caffeine content. And how much gets into your cup depends entirely on how you measure your coffee because for a given bean volume (say one level cup), a light roast will contain more (smaller, denser) beans, and a dark roast will contain less (larger, lighter) beans.

If you measure your beans by the scoop, then a scoop of light roast will contain more beans (and thus caffeine) than your dark roast.

If you measure your beans by weight, then the dark roast’s lower density means the scoop will contain more beans (and thus caffeine) than your light roast.

That’s the simplest explanation.

Any other factors? Well, sure, arabica beans (all Good Earth Roasters coffee is 100% arabica) vary somewhat in caffeine content depending on the coffee plant species. That information’s fairly difficult to obtain, so it’s probably best to assume an average level across all arabica beans. Let’s ignore that difference.

Also, robusta beans, which have more of a harsh and earthy taste, have about twice the caffeine level of arabica beans. Worth the kick? Not to us. 🙂

Finally, caffeine molecules are denatured (break apart) at 235°C. We typically pull our beans somewhere between 200 and 225°C, but a very dark roast – an french, italian or spanish roast – will heat the beans to as much as 249°C, where much of the caffeine is burned off. So here, the rule is for very dark roasts, the caffeine level is always lower.

Bottom line: should you care? In reality, if you’re measuring by weight (which we always recommend), the difference in caffeine levels between a light and a dark roast is fairly small. Not stimulating enough? Have another cup.