What are alkaloids in coffee?

Alkaloids are naturally occurring nitrogen-containing compounds in coffee that affect both how it tastes and how it makes you feel. The most significant is caffeine - the stimulant that blocks adenosine receptors and keeps you alert. Others present in meaningful quantities include trigonelline, theobromine, and theophylline.

Caffeine contributes to bitterness in the cup, though it's only part of the picture - degraded chlorogenic acids also play a role. Trigonelline breaks down during roasting to produce pyridines and niacin, contributing to roasted aroma and some of the characteristic bitterness of darker roasts. Theobromine, found in cocoa too, has a milder stimulant effect than caffeine and a softer, less harsh bitterness.

Alkaloid content varies by species. Robusta contains roughly double the caffeine of Arabica - one of several reasons the two species taste so different, and why a Robusta component in an espresso blend tends to increase both perceived strength and crema. It's also why naturally low-caffeine species like Stenophylla and Laurina are attracting serious research interest as climate pressures reshape what's viable to grow.