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Which Coffee Roast Has More Caffeine? Light Roasts or Dark Roasts?

For years coffee lovers have debated the one simple question; which roast of coffee has more caffeine? Intuitively one would think darker roasts have more caffeine due to the bold flavors and jolt you get when taking a sip. However, many have contented that lighter roasts are more caffeinated because the caffeine burns off in the roasting process. Coffee beans are typically roasted to different degrees in order to bring out specific flavors, but how does this impact the caffeine content?

The fine folks over at Cooks Illustrated conducted a test recently to determine the truth. They used a home roaster and roasted half of the raw, green beans to a light roast and the other half to a dark roast. After grinding the batches separately, they brewed two pots of coffee, using the same volume of ground coffee per batch (1/2 cup per 3 1/2 cups of water), and then sent both batches to a lab for testing. The results came back conclusively. The light roast had 60% more caffeine. It would seem the testing could stop there, but there were still more questions to be answered. 

coffee beans being weighed on a scale

They wondered if the results would be the same if they weighed the grounds as opposed to measuring by volume. Two more pots were brewed to send to the lab, measuring out 1-1/2 ounces of ground coffee per 3 1/2 cups of water. They noticed that it took 2-1/2 more tablespoons of dark roast than light roast to reach 1-1/2 ounces. When the results came back from the lab, they saw that both pots had virtually the same amount of caffeine. So what does this mean?

It turns out that as the beans roast, they lose water and also puff up slightly. The longer the roast time the more pronounced those effects. Dark roast beans will thus weigh less (and be slightly larger) than light roast beans. When the ground beans are measured by volume, the light roast particles will be denser, weigh more, and contain more caffeine than the dark grinds, producing a more caffeinated brew.

So what does this all mean? Well essentially, the only way to ensure that you’re getting the same amount of caffeine with different roasts (with all other variables being equal) is to weigh out your coffee before brewing a pot. If you measure by volume, you’ll end up with more buzz with a light roast than with a dark roast. But if you measure by weight, the caffeine levels will be equal.

Because light roast coffee is roasted for less time, it’s denser and heavier than dark roast. As a result, each particle of ground light roast contains more caffeine than a particle of ground dark roast. When equal volumes are measured, the light roast will thus pack more caffeine.