To misquote Rick James, coffee is a hell of a drug. But as far as coffee's chemical composition is concerned, most of us are in the dark—aside, perhaps, from knowing that caffeine is involved, but even then we’re a little hazy. A new educational video from Reactions and PBS Digital Studios goes surprisingly deep on the complex chemistry and physics that undergird your coffee as it goes from bean to cup, beginning with an examination of the few dozen molecules that create coffee’s aroma. Those include pyridine, which, the video says, has an “earthy smell” (guess that means dirt). Then there’s ethylpropanal, which is “fruity and spicy.” Vanillin speaks for itself. Methional smells like a baked potato. And methanethiol, a sulfur compound, brings the smell of cabbage and garlic.
That’s a lot of disparate smells, which are created through bean roasting—perhaps why coffee has such a distinct, unusual aroma. On to caffeine, that magic chemical that works to block the nerve receptors that tell you you’re tired. In nature, though, caffeine has a different role. “Caffeine, which is actually pretty bitter on its own, is a chemical weapon that can disable or even kill insects that threaten plants,” the video’s narrator says. Caffeine also appears in citrus flowers, to help pollinating insects like bees remember where they’ve been.
Milk, too, has a story of its own. You probably appreciate the way milk looks as it’s poured into a cup of coffee and spreads its creamy tendrils through the dark brown drink. That explosion is the result of diffusion as well as Brownian motion, which is what happens when a bunch of particles in liquid collide. “Studying this dance,” the video says, “was one of the clues Einstein used to prove the existence of atoms.”
Of course, we can’t all scry the secrets of the universe from a cup of coffee. We’ll leave that to the physicists and tasseographers among us.