Coffee rings are probably one of the most mundane -- but irksome -- phenomena in the known universe. Now, a team of scientists know why they have that dark ring right at their edges.
A team of researchers at the University of Pennsylvania have studied the formation of coffee rings to get to the bottom of how they appear on your fine wooden furniture or long-suffering notebook. Turns out their formation depends on the shape of the particles in the liquid. In fact, coffee’s peculiar in containing neat, round particles that pack more densely at the edge. That's why your counter top is never going to look the same as it did when it was new. [YouTube]