NPR: National Public (coffee) Rings

In my typical morning style, cup of coffee in hand, I sat down at my desk and tabbed through my usual news sources for the day. Like any good D.C. Democrat, I started with Politico for my politics fix, then went to Gawker for a little gossip, Washington Post to see what's going down in my city, and finally, my personal favorite, NPR, (which I leave for last because I can listen to the articles). Much to my liking, on today's "All Things Considered" there was an article/newscast on the physics of coffee rings and I immediately though, BLOG!

I'm kind of a sucker for how things work. Science and math have intrigued me from a young age and although I could no longer tell you the formula for the quadratic equation, I still think knowing the itty bitty molecular details of seemingly uninteresting, unimportant things is exciting a great information to store in the back of the brain when you're searching for some coffee table talk. And with no further ado, I present to you...

COFFEE RINGS.

No, not that type, (although I want I want I want!!). 

This type:

I am going to give the brief Samantha Coffee 101 version of the physics behind the coffee ring. I will also post a link at the end of the blog post to the NPR article (video and radio newscast included) reporting the story. Here we go.

When you put a cup of coffee on a table or a napkin, and you have a little spill...

and you leave the spill there to dry you will find that the coffee drys not as one uniformed stain, but with dark, outlined edges. Scientists have discovered that this because coffee is made up of tiny little round particles. Other liquids are made up of elongated ellipsoid particles and when those liquids spill and evaporate the stain drys not like a coffee stain, but as a uniformed blob without any thick, dark edges.

Simple stuff, yet it took physicists and chemists over a decade to figure out. Good thing because what would coffee artists do without the classic dark-edged stain to use in their work:

Click HERE to view the NPR article.