Coffee grains are hard to clean up

[Jame]

Inspired by the recent thread on flying coffee grains I felt the urge to ask if anyone knows why coffee is so darn hard to clean up? It doesn't stick to the rag as most substances do. I'm assuming it has something to do with the grains' surface structure, but what kind of physics describes this?

 

[alxm]

Well, your ability to pick up solids with a wet rag comes from the surface tension of the water, holding the particles in place. That in turn requires you to be able to http://en.wikipedia.org/wiki/Wetting" the surface of the particles. When things are hard to pick up, it's usually because they're hard to wet.

I think the reason coffee grains are hard to wet is because they're quite porous.

 

[sir-pinski]

There are a few factors that contribute to the difficulty of cleaning up coffee grains. One is the surface structure of the grains, as you mentioned. Coffee grains have a unique shape and texture that makes them less likely to stick to surfaces. This is because they have a rough and irregular surface, rather than a smooth and flat one like many other substances.

Another factor is the static electricity that can build up in coffee grains. When you grind coffee beans, friction is created, which can cause the grains to become statically charged. This makes them more likely to stick to surfaces and harder to sweep or wipe away.

Additionally, the oils and compounds in coffee can create a sticky residue that can be difficult to remove. This is especially true if the coffee has been sitting for a while and has dried out. The longer it sits, the harder it becomes to clean up.

Overall, the combination of the unique shape and texture of coffee grains, the presence of static electricity, and the sticky residue they can create all contribute to the challenge of cleaning up spilled coffee. It's a combination of physics and chemistry that makes coffee grains particularly tricky to deal with.