August 28, 2011 Nathan

The Science of Coffee Rings

Coffee rings are a little bit ubiquitous in quirky office focused design. Because they’re the kind of mess that hard workers make. But have you ever stopped to wonder why coffee spillages on paper look the way they do? No? Well. That’s why exists. To answer unasked questions about coffee.

So here you go. This was apparently quite a difficult problem to solve.

“It’s taken physicists more than a decade to figure out why this effect, known technically as “the coffee ring effect,” happens. But now they think they have an answer.”

The answer, according to ten years of scientific study, is that coffee particles are spherical (there’s more info, and a video of what is going on at a microscopic level, at NPR).

The study, at first unrelated to coffee, noticed that when liquids with spherical particles evaporated they formed a ring that looked like a coffee ring. Other shaped particles didn’t.

So, thinking they’d solved the coffee conundrum they put it to the test:

“We went down to the building coffee machine, put 35 cents in, got a cup of coffee, went back upstairs to the microscope, put it on a slide, took a look, and, at least on the micron scale, the particles that we saw were spherical in shape.”

So there you go.

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About the Author

Nathan Nathan is a coffee lover, home roaster, amateur barista and coffee tinkerer. He's married, has two kids, one turtle, and for a day job works for Creek Road Presbyterian Church. He previously worked in PR. This blog is his attempt to make coffee tax deductible.

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