In last week’s Ask Lee, we tackled the question of caffeine content in different varietals of coffee. Concluding that caffeine content is wholly dependent on the individual plant but that there are generalized thresholds for certain varietals. We ended on a cliffhanger of two questions: is there more caffeine in light roasts or dark roasts? How does brew method factor into caffeine content?
Beans undergo a huge number of chemical changes during roasting. To recall last week, caffeine is one of the two key alkaloids in coffee causing both bitterness and buzzes. For most arabica, caffeine starts at one or two percent of the total mass. Once we start applying heat, we simultaneously create and eliminate a swath of compounds – including caffeine. To quote the “Comparative study of polyphenols and caffeine in different coffee varieties affected by the degree of roasting” (catchy title, right?), “light roasted coffee contained a higher overall content of caffeine in all coffees, which exhibited a decrease with intensified roasting”. So, the whole “I am sleepy, give me a bold/dank dark roast” thing is a myth. OR IS IT…
A few Ask Lees back, we explored extraction. The initial ‘surface erosion’ from hot water does the majority of the work to move those volatiles from the grounds into the cup. Coffee is dense due to its highly interlocked woven structure. After the first wave, the remaining hidden away cells slowly saturate and allow more voltatles to migrate into the mug. At this point, saying light roasts have more caffeine runs into an issue. Yes, the roasts might have more but the final cup may have less. In the Thanos-inspired destruction that is roasting (co-Roaster Bruce made me put in this joke), caffeine breaks down – but so do those taut and rigid cellulose cells. Hence, water has an easier time pulling out the caffeine in a darker roast. Imagine water crashing into a sand wall versus one made of bricks. You will end up with much murkier water in the first case. That said, most studies suggest the break down of caffine only happens at a very terminal point, so light to medium to dark will all have similar levels with the drop off point at very, very dark roasts.
Let’s return to the original launch point: why would an Ethiopian coffee make you feel extra twitchy and jittery? The coffee in question would be from In Bloom. As a coffee profiled for espresso (in other words, for high solubility) it would likely have more caffeine in the finished cup. This is despite it having the same original content as other coffees (for example, those caturra varietals from Central America) and having more development, meaning the final roasted beans *could* have slightly lower caffeine than the filter options on the menu.
But for a more developed coffee to have higher caffeine, the extraction must be effective. Meaning on the whole, darker roasts ground and brewed on dodgy equipment usually contain less caffeine in the cup (roll that rim). Yet, if you start with robusta, roast dark, and then extract okay-ish (nineties java-house), you end up with more caffeine by virtue of that starting amount overruling the other variables. Basically, it is a case-by-case or cup-by-cup answer because there is enough paradoxes here to makes me feel like I need another coffee…
Lee Knuttila 