ah… that’s better. now that i’ve had some caffeine, let’srun that back.†what’s going on in that cup of coffee? it might seem mundane, but the closer youlook, the more complex and beautiful it becomes. first off, there are trillions upon trillionsof molecules in the air around that coffee.
is dark roast coffee less acidic, and those hot vapors rising off the cup carrymore than a thousand different types of molecules. a few dozen of those contribute to coffee’sone-of-a-kind aroma. this pyrazine has an earthy smell. methylpropanal is fruity and spicy.
there’s vanillin, you can probably guesswhat that smells like. methional smells like a baked potato. methanethiol is the odor of cabbage or garlic--thanksto a sulfur group, which also shows up in the smells of rotten eggs and skunk spray. most of those molecules are made when thebeans are roasted. the heat of roasting provides the energy toconvert coffee’s bitter chlorogenic acid into all these other compounds, making a richlyflavorful, fragrant and just awesome beverage. many chemical reactions require some energyto get going, even ones that release energy [show gas stove lighting], like combustion.
after all, spending energy is how we makethings happen: cars drive, legs walk, coffee brews. which brings me of course to caffeine, thereason why most of us drink coffee in the first place. the story of caffeine is also a story of evolution. plants didn’t evolve caffeine to help usget through 9 am meetings. like so many of the molecules plants make,caffeine--which is actually pretty bitter on its own -- is a chemical weapon that can disable oreven kill insects that threaten the plants. but citrus plants use caffeine a differentway.
thanks to caffeine’s memory-boosting andever so slightly addictive kick, it helps bees and other pollinators remember the citrusflowers they visit. that gives those plants an advantage in spreadingtheir genetic material--which is, evolutionarily-speaking, what life is all about. so caffeine doesn’t just give you that pleasantmorning buzz. you can also thank it for your orange juice. but back to our own brains. caffeine blocks the nerve receptors that signalthe brain that it’s time to sleep. that’s what helps us power through our bedtime.
speaking of energy… watch that milk swirl and blend with the coffee. that’s diffusion, the process of particlesmoving from an area where there is a lot of the same stuff to an area where there isn’t. diffusion is how breathing keeps us alive. oxygen diffuses from air into our bloodstreamin the lungs, and from capillaries into our cells throughout the body. the way the milk moves here is driven by afew things. it falls due to the force of gravity pullingit down from the carton into the mug.
but then its motion through the coffee isdisrupted by the stickiness of milk and coffee molecules interacting. that and the walls of the mug help set upthose swirling eddies. convection is at play here too. colder, denser milk sinks to the bottom ofthe warmer less dense coffee. this causes the same kind of loops of motionthat happen in liquified rock far beneath earth’s surface. it’s this motion that keeps our planet geologicallyactive. even in the absence of any of these phenomena,milk and coffee will eventually mix anyway.
the particles of milk and little undissolvedcoffee grounds dance thanks to brownian motion: that’s the random movement of particlesas they collide off one another. studying this dance was one of the clues einsteinused to prove the existence of atoms. this spontaneous process of mixing followsthe second law of thermodynamics: that entropy, or disorder, increases over time. your coffee and milk go from two separatesubstances to a mixture, which is less ordered because it’s made of two things all mixedup together. this disorder increase is even more obviouswith the sugar, which goes from a solid, crystalline state--each molecule locked in a pattern -- toa dissolved form, with sugar molecules all
over the place. so it goes with the rest of the universe. rocks crumble to dust. ice melts. and your place keeps getting messier. left to itself for long enough, the entireuniverse will one day reach a state of maximum disorder.
a bit like this milk and coffee. what are we getting at here?
from the largest scale to the smallest, chemistryis everywhere. and once you see it, you'll never look atthe world the same way again.
