It really saddens me to have to include this FAQ. The reality is I hear Barista after Barista tell customers that “light roast has more caffeine than dark roast coffee”. Cue repeated nervous twitch! And so, in hopes that the general public will stop thinking I’m a madman on the loose (well… maybe it will help a little), I write this FAQ...
The answer to the question, leaves us with another question: At what point are you measuring the caffeine? Bean for Bean (roasted / unroasted)? Or brewed in the cup? If so, with what method: espresso; french press, drip, aeropress; chemex pour-over; or... some other method? As you can tell, the answer to the question is complicated.
Allow me to elaborate:
The first reason I hear most often for this incorrect theory is that the heat from the roasting process breaks down the caffeine. This is incorrect. Caffeine is either present at specific levels before roasting or it is not. The roasting process cannot accentuate, nor remove caffeine. Anyone who says otherwise is simply making it up.
When coffee is roasted, it looses weight due to moisture content loss. (We will discuss this at length in a future post). However, said moisture doesn’t simply evaporate taking caffeine with it. Rather, it combines with amino acids and carbohydrates in the bean to caramelize and the process of CO2 emission begins. CO2 does take flavour along with it due to the hygroscopic nature of the bean, however, it does NOT take caffeine along with it. Caffeine is one of the 700 soluble compounds in coffee, yet O2 and CO2 in their gaseous states, do not dissolve the caffeine into the air, otherwise we could simply get our caffeine “fix” from walking into a coffee shop and taking a deep breath.
Next, we must discuss the roasting process. There are so many factors to consider when deciding how to roast a certain green coffee. Included in these are: Altitude grown at, density, moisture content etc etc. Coffees that are better suited to lighter roasting tend toward those grown at lower altitude and of a lower density. The Varietals that are generally used in these growing conditions tend toward those that also have a slightly higher, naturally occurring caffeine level (in reality; fractions of one percent difference), which further propagates the rumour of light roast having a higher caffeine level.
That having been said, bean for bean, light roast coffees may contain a fraction of a percentage higher caffeine level than a dark roast. So, if you are measuring the caffeine level, bean for bean, light roasted coffees would likely contain a very slightly elevated level of caffeine. However this generalization should take into account the varietal as well. If you’re measuring a varietal such as the Maragogype (gigantic bean) versus a Caturra bean (rather tiny bean), then it doesn’t take a rocket scientist to figure out what the results will be.
Further reasons for this question even being considered, relates again to the moisture dissipating during roasting. The longer you roast, the more moisture will leave the bean, rendering the bean lighter in weight at a darker roast. Because coffee is brewed by weight, more dark roast beans are therefore required to make up the same amount (by weight) of coffee than a lighter roast (which weigh more bean for bean due to less time in the roaster and less moisture (weight) loss). Therefore, any fractional difference that was present in the caffeine levels prior to brewing, become completely irrelevant after the brewing process. So, if you are testing the caffeine levels in brewed coffee, you would find caffeine levels very similar, or leaning slightly higher toward the dark roast over the light roast.
The end of the matter, everything having been heard, is simply that this debate is not worth having! 🙂
Any fractional differences between light and a dark roasted coffee is SO slim (in any state: roasted, unroasted, brewed or unbrewed), that if someone claims to be able to notice the difference, they’re probably not being completely truthful! Go with what flavour you like rather than what you think the caffeine level is.