What is caffeine in coffee?

Caffeine is a naturally occurring alkaloid found in coffee beans, responsible for the stimulating effect that makes coffee the world's most widely consumed psychoactive substance. It works by blocking adenosine receptors in the brain - adenosine is the compound that builds up over the course of a day and promotes sleepiness. By blocking those receptors, caffeine keeps you alert.

Caffeine content varies significantly by species and preparation. Arabica beans typically contain 1.2-1.5% caffeine by dry weight; Robusta contains roughly double at 2-2.7%. This is one of the reasons Robusta produces a more intense, harsher cup - the higher caffeine content contributes directly to bitterness. Contrary to common belief, roast level has a relatively minor effect on caffeine content - a dark roast and a light roast from the same green coffee contain broadly similar caffeine levels by weight, though the density change from roasting means the comparison by volume or scoop is more complicated.

For green coffee buyers sourcing decaf, caffeine removal method matters - the various decaffeination processes (Swiss Water, CO₂, Methylene Chloride, Ethyl Acetate, Sugarcane) each remove caffeine to different levels of efficiency, with regulatory standards typically requiring 97% or more removal for a coffee to be labelled decaffeinated.