Why does coffee in a glass leaves its signatory on the surface?

In summary, the conversation discusses the phenomenon of a circle of fluid under a cup of coffee and the possible reasons for its occurrence. Some suggest it is caused by spilled or dribbled coffee, while others mention condensation or residual water in the cup. The discussion also brings up the possibility of water in the wood surface being brought to the surface by the hot mug.
  • #1
Zohar
6
1
TL;DR Summary
How does hot fluid comes down to the surface of the glass it's in?
Some of us may use coffee coaster for our drinks. I was always wondering about that phenomenon and failed to find something on the net yet.
 
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  • #2
Zohar said:
Summary:: How does hot fluid comes down to the surface of the glass it's in?

Some of us may use coffee coaster for our drinks. I was always wondering about that phenomenon and failed to find something on the net yet.
Can you please restate the question, I am struggling to understand what you are referring to
 
  • #3
Haven't you seen a circle of fluid under a cup of coffee? How does it happen?
 
  • #4
Zohar said:
Haven't you seen a circle of fluid under a cup of coffee? How does it happen?

ohh ok, that's what you are referring to ...

Because the coffee has been spilt/dribbled down the side of the cup ... simple as that
 
  • #5
Zohar said:
How does it happen?

it will happen on any cup, drinking glass, bottle of any liquid
and it will happen in a different way if the liquid is cold and it produces condensation
that then runs down the side of the container to the base. This is in addition to any
liquid that rund down the outside surface of the cup etc from what is dribbled/spilt
during the drinking process
 
  • #6
Zohar said:
a circle of fluid under a cup of coffee?
I wonder if you leave your mugs on the side of the sink after washing them up. A small amount of water can stay in the inverted bottom and that can turn up on the table top. Experiment to find if drying up the mug totally will solve the problem. I can't think of any other reason.

Except if there is water in the wood(?) surface which is brought to the surface by the hot mug and then condenses round the cooler periphery to form a ring. Or is the ring in fact due to water and not just a temporary effect of heat on the varnish?

This is a Sherlock Holmes problem.
 

1. Why does coffee leave a ring or mark on the surface of a glass?

Coffee contains oils that are released during the brewing process. These oils can stick to the surface of the glass and create a visible mark or ring.

2. Does the type of coffee affect the mark it leaves on a glass?

Yes, the type of coffee can affect the mark it leaves on a glass. Darker roasts tend to have more oils and therefore may leave a more noticeable mark on the surface of a glass.

3. Can the temperature of the coffee impact the mark it leaves on a glass?

Yes, the temperature of the coffee can impact the mark it leaves on a glass. Hot coffee has more oils and is more likely to leave a mark compared to cold coffee.

4. Is there a way to prevent coffee from leaving a mark on a glass?

Yes, there are a few ways to prevent coffee from leaving a mark on a glass. One way is to use a coffee mug or cup with a non-porous surface, such as ceramic or stainless steel. Another way is to rinse the glass with cold water before pouring in the coffee, which can help prevent the oils from sticking to the surface.

5. Does the cleanliness of the glass affect the mark left by coffee?

Yes, the cleanliness of the glass can affect the mark left by coffee. A dirty or greasy glass can attract more oils from the coffee and result in a more noticeable mark. It is important to clean glasses regularly to prevent this from happening.

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