Ring Around the Coffee Mug

Coffee stained cup

Why does sometimes my half-finished coffee leave a ring around the inside of the coffee mug and sometime it does not? I always make my coffee the same strength, with approximately the same amount of milk and sugar.

How does the coffee then decide whether to stain or not?

Does anyone else experience these staining inconsistencies?

4 comments

  1. It has to do with the amount of humidity in the room. The less humidity the more quickly the surface evaporates leaving behind a residue that gathers at the edges. Sorry, I hope this didn’t spoil any of the mistery.

  2. My word our readers are smart! We’ve been wondering about those mysterious rings for years. We had come to think of them as the ‘crop circles’ of the chickenmonkeydog office.

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