# Coffee rings **URL:** \ **Category:** Factual Questions\ **Created:** [October 4, 2006, 9:16pm UTC](https://boards.straightdope.com/t/coffee-rings/375309 "2006-10-04T21:16:15Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![schrizto](https://avatars.discourse-cdn.com/v4/letter/s/839c29/32.png) [@schrizto](https://boards.straightdope.com/u/schrizto)\ **Post date:** [October 4, 2006, 9:16pm UTC](https://boards.straightdope.com/t/coffee-rings/375309/1 "2006-10-04T21:16:15Z")
Can someone explain how when coffee is spilled a ring is formed around the edge of the spill, while spills of other liquids do not? Is it something only in the coffee that does this? ---
**Author:** ![spingears](https://avatars.discourse-cdn.com/v4/letter/s/ebca7d/32.png) [@spingears](https://boards.straightdope.com/u/spingears)\ **Post date:** [October 4, 2006, 10:03pm UTC](https://boards.straightdope.com/t/coffee-rings/375309/2 "2006-10-04T22:03:23Z")
[QUOTE=schrizto] Can someone explain how when coffee is spilled a ring is formed around the edge of the spill, while spills of other liquids do not? Is it something only in the coffee that does this? [/QUOTE] WAG Surface tension? ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [October 4, 2006, 10:39pm UTC](https://boards.straightdope.com/t/coffee-rings/375309/3 "2006-10-04T22:39:21Z")
The key is probably the botom of the mug - it touches the table as a ring, rather than a disk, as in a typical tumbler or “iced tea” glass. ---
**Author:** ![susan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/susan/32/17537_2.png) [@susan](https://boards.straightdope.com/u/susan)\ **Post date:** [October 5, 2006, 1:32am UTC](https://boards.straightdope.com/t/coffee-rings/375309/4 "2006-10-05T01:32:09Z")
I don’t have the experience you do. I perceive that most, if not all, fluids leave rings. Maybe the difference is the kind of cup you use. I drink just about everything out of a mug. ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [October 5, 2006, 3:01am UTC](https://boards.straightdope.com/t/coffee-rings/375309/5 "2006-10-05T03:01:06Z")
A professor in my department actually investigated this question some time back. [Here’s an article on it](http://chronicle.uchicago.edu/971023/coffee.shtml). ---
**Author:** ![Beware\_of\_Doug](https://avatars.discourse-cdn.com/v4/letter/b/278dde/32.png) [@Beware\_of\_Doug](https://boards.straightdope.com/u/Beware_of_Doug)\ **Post date:** [October 5, 2006, 3:33am UTC](https://boards.straightdope.com/t/coffee-rings/375309/6 "2006-10-05T03:33:50Z")
You can spill your coffee and get one of [these](http://www.landolakes.com/mealIdeas/ViewRecipeLarge.cfm?RecipeID=6326B)? I’m drinking the wrong brand of coffee. ---
**Author:** ![schrizto](https://avatars.discourse-cdn.com/v4/letter/s/839c29/32.png) [@schrizto](https://boards.straightdope.com/u/schrizto)\ **Post date:** [October 6, 2006, 7:37pm UTC](https://boards.straightdope.com/t/coffee-rings/375309/7 "2006-10-06T19:37:08Z")
Actually, what I alluded to in “coffee rings” wasn’t the ring that is formed by a mug, but the dark ring that appears when a coffee spill dries up. ---
**Author:** ![Hampshire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hampshire/32/4887_2.png) [@Hampshire](https://boards.straightdope.com/u/Hampshire)\ **Post date:** [October 6, 2006, 7:49pm UTC](https://boards.straightdope.com/t/coffee-rings/375309/8 "2006-10-06T19:49:11Z")
I think the cup or mug is what creates the ring. Coffee spills down the side of the container then moves along the edge of the ring. I don’t think you can just pour some coffee on a flat surface and have a ring magically form. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [October 6, 2006, 8:03pm UTC](https://boards.straightdope.com/t/coffee-rings/375309/9 "2006-10-06T20:03:09Z")
[QUOTE=schrizto] Actually, what I alluded to in “coffee rings” wasn’t the ring that is formed by a mug, but the dark ring that appears when a coffee spill dries up. [/QUOTE] **MikeS** got it then:[Here’s an article on it.](http://chronicle.uchicago.edu/971023/coffee.shtml) Basically, there’s more evaporation at the edges of the drop than in the middle, so solutes are drawn to that outer ring. I’ve seen the same effect with colored Kool-Aid. ---
**Author:** ![Hampshire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hampshire/32/4887_2.png) [@Hampshire](https://boards.straightdope.com/u/Hampshire)\ **Post date:** [October 6, 2006, 8:05pm UTC](https://boards.straightdope.com/t/coffee-rings/375309/10 "2006-10-06T20:05:57Z")
[QUOTE=Hampshire] I think the cup or mug is what creates the ring. Coffee spills down the side of the container then moves along the edge of the ring. I don’t think you can just pour some coffee on a flat surface and have a ring magically form. [/QUOTE] Sorry, I thought you were talking coffee rings [like these](http://www.camarada.org/images/postcard_ab3.jpg) ---
**Author:** ![susan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/susan/32/17537_2.png) [@susan](https://boards.straightdope.com/u/susan)\ **Post date:** [October 7, 2006, 3:28am UTC](https://boards.straightdope.com/t/coffee-rings/375309/11 "2006-10-07T03:28:12Z")
As did I.