Light vs Dark - Two Tales of Caffeine

There’s a myth in the coffee world- well, actually, there are two versions of this myth. The first one is based on physical sensory and the effects of caffeine, and it goes, “lighter roasts have a higher caffeine level because less of the caffeine is cooked off during the roast.”

The second version is also based on physical sensory of the taste buds, observing that dark roasted coffee has more “kick” to it. A punch in the face, as it were. There’s a little truth to the 1^st version, but the why is not so obvious at first.  Let’s investigate.

We’re going to talk a little chemistry.  The boiling point of Caffeine is 455℉.  Only the very darkest roasts ever get to those temps, and even then, the caffeine is inside the bean, meaning unless the beans are very charred, maybe to Italian Roast, the caffeine will remain inside the bean, or at least have minimal loss during the roast. At Burr Roasters, 453 ℉ is the very highest temp our coffee ever gets and that’s the only in our two darkest roasts.  Additionally, although there is some sublimation occurring at lower temps, it’s not significant enough to cover here.

So, if it’s not the light roast that has more caffeine and not the dark roast, with all its punch in the face, burnt toast flavors, which one has more caffeine?

The truth is, they both have about the same caffeine when measured by weight. Cook’s Illustrated ran an experiment, where they measured the caffeine levels for two samples, a light roast and a dark roast. For control, the testers used 6.5 tbsp. of coffee to 28 oz of water using a light roast and a dark roast and their findings showed that the light roast had more caffeine.  However, when they ran the test by weight, they found the caffeine levels the same.  They also found that the dark roast coffee needed 2-1/2 more tbsp. (9) than the light (6.5), to weigh in at 1-1/2 oz, indicating that weight is an important factor in consistent coffee brewing.

During the roasting process, coffee beans expand, like popcorn, filled with CO2 and gaseous H20. Think of dark coffee as fluffier than light roasted and light roasted as fluffier than green coffee.  Green beans are seriously dense, to the degree that they will ruin your grinder if you continue to run them in it. 

In the image below, imagine the black box is your scoop. By measuring in a scoop, you will get more bean for a light roast vs scooping a dark roast.  

Diagram, not to scale, of different roasts when measured by volume.

See how more green coffee fits in the box than the dark roast? Smaller beans. More caffeine per scoop.  now let's look at coffee by weight.

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Each one of these samples weighs the same, so if you're measuring by weight, you'll find the same number of beans, the same amount of total dissolved coffee solids (coffee strength) and the same amount of caffeine. 

The point to all this is, you can have more consistent coffee and caffeine levels by investing in a small kitchen scale. They are inexpensive and will improve your coffee experience every day! Use our handy and simple coffee:water ratio chart to find a  good starting point and adjust as necessary.

So private, when your crabby old NCO says "Make it dark and make it strong!" you can say, "1SG, I think you need to invest in a scale to regulate your caffeine intake." Good advice, Soldier. good advice.