When you leave coffee in a mug,...?

Question

why is there only a brown rim at the top, and not all the way down the mug?

Answer 1

If like the old cowboys you don't wash your cup every day, and just refill it frequently, it will get a brown stain all the way down. My dad and granddad didn't ever want their cups washed. These things were icky when they finally did hit the dishpan!! They didn't want the coffee pot washed either.

Answer 2

There are oils in coffee which float to the top and collect in a ring around the cup as the coffee cools.

Answer 3

hmmmmmmmm. im having a cup now...i see what your saying