Do you have a fascination with all things coffee? Ever wondered why spilled coffee leaves a ring-shaped stain on the surfaces of things? We find all things coffee fascinating, actually, but we’re intrigued at how even small drops of coffee dry with most of the spilled content formed into a ring. The phenomenon shows a perimeter that’s noticeably darker than the center. It’s a suggestion of some cool chemical process going on, and one that we thought you might want to know the science behind.
Why Does Spilled Coffee Form a Ring?
What is going on with coffee that makes its composition show separation on a paper towel or other surface? The University of Chicago attempted to answer that question and to show how the solute in coffee segregates from the solvent. Participants in the study focused their research on the mechanisms that might drive the divide, and here’s what they found.
“We have determined that ring formation is a ubiquitous and robust phenomenon. It doesn’t depend on the solute, the solvent, or the substrate so long as the solvent is partially wetting and volatile, and the contact line is pinned,” researchers said.
Coffee Ring Stains Don’t Follow the Rules
The University of Chicago researchers went on to explain that the traditional mechanisms of solute transport, “Marangoni flow, Rayleigh-Benard convection, diffusion, electrostatic and electro-kinetic effects, and wetting phenomenon,” do not apply to coffee ring stains. They reported that coffee rings are caused by capillary flow, which has not been studied much, and they suggested that contact drops of coffee are pinned and that any liquid “evaporating from the edge must be replenished by liquid from the interior.”
They stated that since evaporation is the driving method of creating these coffee rings, it’s possible to alter the evaporation profile of the liquid to make different types of deposits.
What does this research say about the coffee you’re drinking? Not too much, but it’s exciting to know that coffee can be enjoyed as a beverage, and it can be studied to perhaps lead to new discoveries, too. For instance, did you know that UCLA (University of Los Angeles) researchers are studying coffee rings as part of their research on disease? Coffee, a universal beverage, may have even more benefits to mankind than calming stress, promoting happiness, and bringing people together.