One question we get asked fairly regularly is if it’s true that a light roast has more caffeine. It’s a reasonable question and the short answer is that it’s about the same either way. However, only viewing caffeine levels in relation to roasting is too narrow of a looking glass and in anything it leads down a path of general confusion and misinformation.
Now, for a combined crash course in general botany, chemistry and organic chemistry, read on.
Coffee is a plant, a tree shrub to be exact. Plants by nature produce an inordinate amount of chemicals and secondary compounds. Chemicals are bonds and interactions of compounds found within the periodic table of elements. In botany secondary compounds are compounds produced by a plant that aren’t necessary for its primary metabolic growth and nutrition functions. Primary metabolites include things like photosynthesis, respiration protein building, lipids, and carbohydrates – without these the plant has a zero chance of living. So, secondary metabolites are the substances produced beyond the basic, primary living function. One of the groups of secondary metabolites are called alkaloids.
Alkaloids brings us to caffeine. An alkaloid is a nitrogen-based, organically occurring chemical compound of a plant origin which has a physiological effect on humans and animals. Caffeine is just one of those alkaloid chemicals. Other alkaloids you probably know include: nicotine, cocaine, quinine, ephedrine, and opium drugs like morphineand codeine.
So, what we know so far is caffeine is one of many alkaloid chemical compounds produced by plants. Notice we said plants, not coffee. This is because people tend to automatically equate caffeine exclusively with coffee and to a lesser extent, tea. But the caffeine alkaloid is actually produced by some 60 different species of plants, including: cacao beans, yerba maté, kola nuts, and guarana (often used in energy drinks & weight loss supplements). Caffeine’s role in nature varies, but in general it is produced by the plant as 1) An insecticide or sterilant to defend against harmful insects and, 2) As a stimulant in the flower’s nectar to attract and energize bees and other pollinating creatures.
When it comes to the coffee plant, Rubiacea Coffea, there are two primary species in commercial use, Arabica and Robusta. Within the arabica and robusta species there are literally hundreds of common cultivar and hybrid varieties. At any given time your local roastery café probably has half a dozen to a dozen different varieties of the Coffea plant. The caffeine content within a coffee seed (bean) fluctuates, sometimes widely, between every Coffea species, variety and hybrid.
The above graph pointed illustrates that the primary driver of caffeine content in coffee has more to do with the plant’s biology than anything else. A lot of people still think that coffee just sort of happens. They don’t know that coffee is a crop with growing regions, seasons and harvests, let alone that it has different species and varieties. Moreover, people generally base their purchase on either the perceived acidity level or a country of origin, such as, Ethiopia, Brazil, Sumatra, etc, but farmers don’t plant fields will all the same variety. So, even within a single bag of a single origin, single farm coffee you‘re not likely to see beans will similar caffeine levels.
Regarding roasting level and caffeine. Roasting is a dry heat cooking method and the chemical thermodynamics of roasting coffee are extremely complex. The whole point of roasting is 1) to degrade the cell structure so the coffee can be ground for brewing, and 2) to augment the desirable flavors and aromas already contained within the bean. In specialty coffee, caffeine isn’t the goal – brewed flavor is. One consequence of roasting is that the thermal decomposition of methylxanthine stimulants (caffeine, theophylline and theobromine), so, yes, caffeine levels do decrease in darker roasters, however, when you look at the temperature degredation of caffeine, coffee roastingtemperatures are insufficient to sublimate (evaporate) caffeine from its chemical matrix. So, in reality the caffeine loss during roasting of any degree is negligible.
So, back to our original question, “Is it true that a light roast has more caffeine than a dark, or vice versa?” Roasting darker will slightly impact caffeine levels, yes. If you’re drinking only a light roast for more caffeine or a dark roast for less, then your approach is mistaken, because, as we’ve explored, the plant variety has far more to do with caffeine levels than roasting ever will.