When spilled coffee dries on my kitchen counter, it forms a brown ring, with very little inside. Why is that?

Question

When spilled coffee dries on my kitchen counter, it forms a brown ring, with very little inside. Why is that?

Answer 1

this is because the coffee spills a little over the rim of the mug and then drips down to the counter. when you pick it up the mug tries to attach the coffee to itself because its trying to act as an insulating atom, which means it looks for weaker atoms to bring with it such as your coffee which is a conductor. the coffee then is pulled down by gravity because the force of gravity is stronger than the pull of the insulator. the coffee seperates and clings back to the atoms of coffee in the original ring.

:] there is your full explanation sweetie great question.

Answer 2

It seems like many people are answering a question you didn't ask.

When a drop of spilled coffee dries on a surface, the outermost part dries first (because the drop is not as thick as it is at the center).  When the outer part dries, capillary action causes the remaining liquid to "fill in" the dried part, trying to reliquify it.  That too dries, and capillary action keeps this process going until the drop is fully dry and almost all of the coffee is congregated around the outer edge of the drop.

Answer 3

Because you are to lazy to wipe it up right away maybe.

(capillary attraction draws the coffee to the rim of the coffee cup sitting in the middle if the puddle of spilled coffee)

Answer 4

from what you described it sounds like the coffee just cant get to the inside if im picturing it right.

when the coffee spills over the rim of the cup it can not leak underneith the cup due to the round base of the mug.

it just stays in the circle.

:)

Answer 5

When the spilled coffe is under a cup, the ring is caused by capillar attraction of the cup's lower ring.

The coffe "sucks" itself to the little space between the round cup's bottom edge and the table it's sitting on, where it dries in a circular shape.

The middle of the ring is the part, where the mug sits on the table. So there is not much space for the coffee.

However on the inner and outer edges of the cups bottom rim, there is more coffee clinging on the cup, and therefore more brown coffee can dry up, discoloring the table more.

If you mean a "freely" spilled stain, the brighter inside comes from the fact, that the puddle will dry out from the outside in.

This means, that the stain is liquid in the middle longer than the outside.

If you have a cup of coffee, and you take only small sips and set the cup down again, you will see circular lines on the inside of the cup, where the coffee dried where the coffee's surface meets the cup.

The same happens on the table. The coffee evaporates, and the stain slowly shrinks while drying up.

The middle keeps the coffe fluid for longer, while the coffee at the edges dries into the table.