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I've only gotten answers about normal coffee, like with milk in it. There is nothing about black coffee so could you help me? Is it a solution, colloid, or suspension?

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That depends how the coffee is prepared.

Coffee prepared via the drip method is typically a solution. You can dilute it as much as you like and will never find suspended solids. Coffee prepared in this way generally does not contain the fats and gasses that coffee prepared in other ways would because this method does not use pressurized extraction and because this method uses a paper filter.

Coffee prepared as espresso through the use of a pressurized system like an espresso machine is all three things: a solution, a suspension, and a colloid. In these machines, paper filters are not used, which allows some of the oil from the beans and some very small fragments of grinds to be captured in the brew, creating a suspension. Also, the force of the pressurized extraction causes gasses in the bean to be extracted into the final brew, creating crema. The crema is a colloid of water, the aforementioned gasses, and the aforementioned fat.

Other methods will produce varying results depending on the combination of brewing mechanism (pressure, immersion, or percolation) and use of a paper filter vs. metal filter.

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  • "Coffee prepared via the drip method is typically a solution." It's not transparent, though, which all solutions are.
    – nick012000
    Nov 5, 2021 at 10:08
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    @nick012000 Solutions are not all clear and transparent. Imagine a solution of gold in mercury. Certainly not clear or transparent! In the case of solutions where water is the solvent, they typically do have a degree of transparency. That doesn't mean perfectly transparent, though. Take your diluted drip coffee, put some in a glass cup with smooth walls, and shine a laser or bright light through. That'll give you a better notion of it because floating molecules in suspension will reflect light. Alternatively, let that cup of coffee sit for a few days. It will never settle.
    – R Mac
    Nov 5, 2021 at 11:18
  • Wouldn't a combination of mercury and gold be an amalgam, rather than a solution, though? I don't think that counts.
    – nick012000
    Nov 5, 2021 at 20:35
  • Amalgams are solutions. Specifically they're solutions of some metal in mercury. That's all the word "amalgum" means, actually. Fun facts.
    – R Mac
    Nov 6, 2021 at 13:56
  • Actually, I should add a bit of explanation. You can find easy evidence of this in the role of mercury in gold mining. Since gold amalgamates readily, cracks in chunks of ore would be injected with it, then the mercury collected. Afterward, the miner would heat the mercury solution to boil away the mercury, leaving behind the gold. This would not be at all likely if mercury truly reacted with gold in a chemical way.
    – R Mac
    Nov 6, 2021 at 14:00

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