Is Light Roast Coffee Caffeine-Richer?
The myth: light roast coffee beans retain more caffeine since they are roasted less.
The caffeine difference between light and dark roast coffee is negligible.
However, there is something to the concept of coffee density, which is why so many people are perplexed by it.
When comparing the caffeine concentration of light and dark roasts, keep in mind that dark roasts lose density and the beans grow in size during the roasting process (imagine if you kept roasting until it turned to ashes).
If we measure coffee by volume (1 tablespoon), light roast coffee will contain more individual beans than dark roast, since dark roast beans are larger and fit into the scoop less easily. As a result, the scoop of mild roast would have more caffeine.
The size of the beans doesn't matter if we measure by weight (25 grams); just the bulk does. So, while it may appear that you have more dark roast beans (because to their size), you fact have the same number. The amount of caffeine in both drinks would be about the same.
The brew process, not the roast, determines how much caffeine is in the cup. When it comes to brewing methods, espresso is stronger than drip coffee ounce for ounce, but you drink less overall. People may equate dark roast's "strong flavor" with "more caffeine" since espresso has a rich, thick flavor comparable to dark roast. Unfortunately, it's simply another urban legend.