Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How does hot water brew coffee?

  1. Sep 24, 2014 #1
    I wondering what actually happens when you brew coffee (or tea) with hot water. Every source I can find simply talks about how long you need to brew it to "draw out" the flavor or "release" the caffeine. I'm interested in what's actually physically happening to the coffee grounds that makes it change the water into coffee. If it was just that particulate matter got into the water, there wouldn't be need for hot water. Is it that some small component of the coffee ground is actually changed from a solid to a liquid from the hot water and gets mixed with the water? Or maybe there's some microscopic pockets in the coffee ground which when heated expands and pops open releasing stuff into the water? What's actually going on? Thanks!
  2. jcsd
  3. Sep 24, 2014 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

  4. Sep 24, 2014 #3

    Doug Huffman

    User Avatar
    Gold Member

    OP has touched on some of the physical phenomena of brewing tea or coffee. They can be brewed with cold water but they are primarily diffusion processes sped up by the heat. The heat swells the woody cells of the plant material, increasing the area for the diffusion. A parameter that is controlled is diffusion path length by controlling the grind grain size as a function of time of exposure to the diluant water. There is probably some temperature effect on the chemicals solubility but that's beyond me. I just know how to brew a good cuppa from the cheapest bens that I can find.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook