Interesting phenomena of boiled water and my coffee.

In summary, the conversation discusses a unique coffee filter that uses a plastic container with a filter paper sachet filled with ground coffee to drip coffee into a cup. The person notices fizzing in the hot water when trying to make coffee and wonders if it is due to the hot water heating the air inside the glass or the coffee trying to drip into the glass raising the pressure. They conclude that the most likely explanation is the air pressure being increased and observe that breaking the seal speeds up the dripping process.
  • #1
BOAS
552
19
Hello,

whilst making my coffee this morning (more like this afternoon, but hey I'm a student), I noticed something that I thought was cool and I'm interested in hearing what you guys think may be happening and/or what you have to say about my ideas.

So, I have these 'coffee filters' that are halfway between proper coffee and instant coffee. They are essentially open plastic containers with a filter paper sachet filled with ground coffee as the base that fit in the top of a coffee cup. You pour boiling water into the top and the coffee drips down into the cup.

I poured the water into the top and walked away to put my bread in the toaster. I came back and noticed no coffee had dripped through, but there was fizzing in the hot water. Enough that little droplets were being thrown a few centimeters above the surface.

The coffee filter creates a reasonably tight seal around the cup so what is going on?

Is the hot water heating the air inside the glass raising it's pressure and forcing it out through the water, or perhaps the coffee trying to drip into the glass is raising the pressure by decreasing the volume the air can occupy. Or is there something stranger going on causing the water to reach boiling point again?

I know this is lacking in the physics side of things, but it would be cool to understand why.
 
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  • #2
Is the hot water heating the air inside the glass raising it's pressure and forcing it out through the water
That looks like a possible explanation. Bubbles of air can look like boiling water, even without actual boiling. And if you have no other way for air to escape...
or perhaps the coffee trying to drip into the glass is raising the pressure by decreasing the volume the air can occupy
I thought no coffee had dripped through?
 
  • #3
Thanks for the response.

mfb said:
That looks like a possible explanation. Bubbles of air can look like boiling water, even without actual boiling. And if you have no other way for air to escape...
I thought no coffee had dripped through?

Yeah, that does seem like the most likely explanation and yes, no water had dripped through so that idea is unlikely.

I think this further observation strengthens the idea of the air pressure being increased; If I break the seal by lifting the container out of the glass for a moment, equalising the pressure, coffee begins to drip frequently, whereas if I leave it to it's own devices it can take upwards of a minute for anything to happen!
 

Related to Interesting phenomena of boiled water and my coffee.

1. What causes the "swirling" effect in boiling water?

As water is heated, convection currents are created. This means that the hotter water rises to the top, while the cooler water sinks to the bottom. This movement of water creates the swirling effect that we see in boiling water.

2. Why does my coffee taste different when I use boiled water compared to cold water?

The temperature of the water can greatly affect the taste of your coffee. When water is boiled, it releases more oxygen and other gases, which can enhance the flavors of your coffee. Additionally, boiling water can extract more oils and flavors from the coffee beans, resulting in a more robust taste.

3. How does boiling water affect the solubility of substances?

Boiling water increases the solubility of substances, meaning that more of the substance can dissolve in the water. This is because the heat from boiling breaks down the bonds between the molecules of the substance, allowing them to spread out and dissolve more easily in the water.

4. Can boiling water remove impurities from water?

Yes, boiling water can remove some impurities from water. When water is boiled, the impurities, such as bacteria and viruses, are killed off due to the high temperature. However, boiling water does not remove all impurities, such as chemicals or heavy metals, so it is important to filter your water if you suspect it may contain these substances.

5. How does boiling water affect the structure of water molecules?

Boiling water causes the water molecules to move faster and further apart from each other. This results in a decrease in the density of the water and an increase in the amount of space between the molecules. This is why boiled water can appear "lighter" or clearer compared to cold water.

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