The chemistry inside a cup of coffee

Today’s Video of the Day comes thanks to the American Chemical Society’s YouTube channel Reactions. The clip takes an in-depth look at the chemistry of coffee and how it relates to the evolution of plants and the world around it.

Coffee is perhaps best known for the potent dose of caffeine it provides. In humans, caffeine blocks the nerve receptors in our brains that tell us it’s time to rest, giving us that extra kick.

As plants evolved, caffeine was developed as an adaptation used as a chemical weapon against predatory insects that threatened the plant. Citrus plants even have a bonus use for caffeine. Because the chemical posses the ability to boost memory and energy, it helps bees and other pollinators remember the citrus plants that they have visited. As a result, those plants get an added evolutionary advantage in spreading their genetics.

When milk is poured into coffee, colder dense milk sinks to the bottom of the warmer, less dense coffee. This convection current is very similar to the way in which liquified rock moved beneath the Earth’s surface. This type of motion is how Earth stays geologically active.

But even without convection currents, milk and coffee would ultimately mix anyway. The undissolved coffee grounds and milk particles interact in what is called Brownian motion, or the erratic, random movement of microscopic molecules in fluid. According to the second law of thermodynamics, entropy, or disorder, increases over the course of time. Thus, two separate substances mix into one, less ordered substance.

When sugar is added, the mixture becomes even less ordered. As each sugar molecule dissolves, it goes from a solid, locked state to sugar molecules being scattered about. A similar pattern can be seen all over the planet when ice melts or rocks break down into dust.

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By Rory Arnold, Earth.com Staff Writer

Source: American Chemical Society