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The great caffeine debate

“Which of these has the most caffeine?”

The Caffeine Debate -- Light or Dark Roasted?

“Which of these has the most caffeine?”

I love it when this question pops up, which it does at least once a week it seems. Some people are looking for joe with a jolt, some are trying to reduce their jitters, and others are just curious. So, let’s settle the mystery of what coffee has the most caffeine.


First off, let’s agree to ignore any coffees that have caffeine intentionally added to them, or coffee from Robusta type beans(they are much higher in caffeine). These don’t count. And, by the way, exceptionally few coffee roasters test their finished product for caffeine content. You will find these figures on some canned products or coffee brands that are trying to differentiate themselves with high caffeine levels.


Ultimately, the debate is usually whether light roasted coffees or dark roasted coffees have more caffeine. Here’s the answer: it depends. But maybe not in the way you’re initially thinking.
Caffeine is a complex molecule that occurs naturally in more than 60 plants including coffee beans, tea leaves and kola nuts, to name a few. It’s also made synthetically and added to some medicines, foods and beverages. It’s a stimulant that is understood to block adenosine receptors leading to increased dopamine and glutamate. The increased presence of these two compounds make us feel happy and get us moving. Caffeine works in our bodies in other ways too, but this mechanism is believed to be the primary explanation of the effects we experience.

Back to our debate… The green coffee we start the roasting process with will have slightly varying levels of caffeine, based on growing climate, cultivar, and other factors outside our control. Again, this is something that roasters rarely test, and it could be different even from bag to bag or bean to bean, so we’re going to ignore this factor as well.


Once we start roasting the coffee, two important things happen. Water molecules inside each bean start to evaporate as steam. At the same time, the bean itself begins to expand. The longer we roast, the more water is driven off and the larger the bean gets - up to a certain point, beyond which we’re talking about something that’s so burnt we wouldn’t call it coffee anymore. We’d call it “burnt compost.”


Assuming that we are roasting a typical batch however, if we stop at a light roast, we will end up with coffee beans that still have water (and the associated weight of the water) and haven’t expanded much. If we push on to a dark roasted coffee, we will have beans with far less water and are thus individually lighter and larger than their light-roasted compatriots.
So dark-roasted beans are going to be lighter and larger than the light-roasted beans. Here’s where the ‘it depends’ comes into play. How do you measure out your coffee when you brew it? If you measure out your beans with a scale to brew (which will always be a more consistent cup of coffee), then your dark-roasted coffee is going to pack more punch because unlike water, caffeine is not driven out of the bean by the roasting process. To break down caffeine, you need a chemical reaction that doesn’t occur during the roasting process.


If you measure your beans out with a scoop, then your light-roasted coffee is likely to give you more boost, because you’re actually putting more beans into each cup.


If you don’t grind your own beans and are weighing or scooping from coffee that’s already ground, guess what… the caffeine amounts are probably about the same now. Because the difference in weight to volume ratio is now mostly erased by being already ground, you’re putting roughly the same amount of actual coffee into your brewer by weight or by scoop, so light or dark doesn’t matter anymore.
So, here’s the summary:
  • If you grind your own beans, dark-roasted coffee will likely have more caffeine in your cup if you weigh out your whole beans on a scale before grinding and brewing.
  • If you grind your own beans, light-roasted coffee will likely have more caffeine if you use a scoop to measure your whole beans.
  • If you weigh or scoop from coffee that’s already ground, it probably doesn’t make any difference whether it’s light or dark.


After all that, I’m ready for another cup. Thanks for reading, and remember EVERYONE deserves great coffee!

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