How does roasting affect the caffeine content in coffee?

Roasting does influence the perceived caffeine content of coffee, and the premise that lightly roasted coffee may have slightly more caffeine than dark roasted coffee is based on the way roasting affects the beans. During the roasting process, coffee beans expand and lose moisture, which changes their density and weight.

While the actual caffeine content by weight is relatively similar across roasting levels, the key distinction comes from the way coffee is typically measured for brewing. When comparing equal volumes of coffee (rather than equal weights), lightly roasted beans are denser and more compact than dark roasted beans. Therefore, when brewed using the same volume of coffee, the lighter roast can yield a slightly higher caffeine extraction due to this difference in density, even if the absolute caffeine content by weight doesn’t differ significantly.

In practice, though, the difference in caffeine levels between light and dark roasts is minimal and often overstated; many factors, including brewing method and extraction time, also play crucial roles in the final caffeine delivery of any cup of coffee. This nuanced understanding reinforces why the statement that lightly roasted coffee contains slightly more caffeine than dark roasted coffee holds validity.