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Why is grinder heat a problem?

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  • Why is grinder heat a problem?

    It has always confused me that grinder brands and sellers talk to the reduced heat from a motor being a selling point (on premium home grinders especially) but on the other hand we’re told to preheat a portafilter before use. In my mind my portafilter is bloody hot (hot to touch) after some time. And surely this heat is far greater than the heat generated by the grinder motor and imparted on the ground coffee a moment earlier… Commercial grinders aside one perspective seems wrong. And for the record a warm portafilter makes sense to ensure a stable and consistent temperature when creating espresso. So why is a little heat generated from a home grinder a problem and does it actually create more heat than more 80* portafilter?

  • #2
    Assuming that you are going to brew the coffee soon after grinding, the biggest issue is inconsistency in the temperature of the grinds, which flows through to the consistency of extraction. That is obviously more of a 'problem' if you are grinding several doses back to back. The idea, as I understand it, is that hotter grinds result in faster extraction, so you have to grind finer. Now, precisely how material these differences are for a home user is another point entirely.....

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    • #3
      Thought it was more about bean heat than motor heat. The faster the RPM the hotter the beans get and to much heat can start a premature chemical reaction in the beans. That's what I understand. Anyone?

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      • Blues1143
        Blues1143 commented
        Editing a comment
        this is my basic understanding also.

      • Lyrebird
        Lyrebird commented
        Editing a comment
        I don't believe the problem is one of reactions: coffee is reasonably chemically stable.

        Many of the essential flavour compounds are quite volatile and the vapour pressure will rise with temperature: it is usually an exponential function (Clausius Clapeyron Equation). Since the surface area takes a big jump from grinding, elevated temperature at this stage will accelerate the loss of volatiles.

      • tompoland
        tompoland commented
        Editing a comment
        Lyrebird I was just about to say the same (not). Very impressed with the distinction you made between chemical and compounds. Now going to dust off my Oxford Dictionary.

    • #4
      But wouldn’t that same reaction start in a hot portafilter?

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      • Blues1143
        Blues1143 commented
        Editing a comment
        yes but starting earlier from the grinder

      • Lyrebird
        Lyrebird commented
        Editing a comment
        In my opinion time in a hot portafilter has a very perceptible negative effect on coffee quality.

        I am terribly distractible and occasionally drift off on a train of thought in the middle of making a coffee. I have learnt that if I don't get back to it within a minute or two I am better off starting again.

      • Barry O'Speedwagon
        Barry O'Speedwagon commented
        Editing a comment
        Well I guess it's trued that I've never experimented with leaving grinds in a hot portafilter for a minute. I get distracted at different times in the process.

    • #5
      Originally posted by Danptheman View Post
      But wouldn’t that same reaction start in a hot portafilter?
      What proportion of the grinds are exposed to the hot portafilter, and for how long, before the water hits the puck? Not a lot I'd guess.

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