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  • Why do we worry about grinders heating grinds to 30°C+...

    ... When the next thing we do is put the grinds in a 80°C+ PF for a reasonably extended period before they see a drop of water?

    Serious question. Have I missed something?

  • #2
    Originally posted by Dragunov21 View Post
    ... When the next thing we do is put the grinds in a 80°C+ PF for a reasonably extended period before they see a drop of water?

    Serious question. Have I missed something?
    Let me ask you a question.... why would your ground coffee be sitting in your portafilter "... for a reasonably extended period of time"? As far as I am concerned, it should only be a few seconds before it has water running through it.

    Also... I think you will find that friction heat of a grinder running at 1380rpm will far exceed 30-ish degrees and the worry would be all about how this additional heat may bake or even burn the coffee.

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    • #3
      Re: Why do we worry about grinders heating grinds to 30°C+...

      Probably because the rate of oxidation, and also the rate of vapourisation of coffee oils, increases with temperature.
      So it would be like leaving the grounds in the PF on the bench longer.

      Also, certain reactions may occur at higher temperatures which may otherwise not occur ('burning' in the extreme case).

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      • #4
        Why do we worry about grinders heating grinds to 30°C+...

        I did a short espresso course at Padre last week, and one of the things they mentioned when talking about how they adjust the grind through the day was the heat effect if the grinder has been going constantly during a busy period.

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        • #5
          Why do we worry about grinders heating grinds to 30°C+...

          I'm surprised that commercial grinders don't include active cooling if heat is such an issue. It's seems like an obviously solution for grinders that would otherwise overheat.

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          • #6
            Originally posted by fruity View Post
            I'm surprised that commercial grinders don't include active cooling if heat is such an issue. It's seems like an obviously solution for grinders that would otherwise overheat.
            Some do... and... others use a gearbox to drop rpm to a much cooler 400 rpm (or thereabouts)... and then there are the super-duper machines with both fan cooling and gearboxes

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            • #7
              Why do we worry about grinders heating grinds to 30°C+...

              Well there you go... you learn something new every day! :-)

              Comment


              • #8
                Originally posted by Vinitasse View Post
                Let me ask you a question.... why would your ground coffee be sitting in your portafilter "... for a reasonably extended period of time"? As far as I am concerned, it should only be a few seconds before it has water running through it.
                Do you grind into a PF? Then your grinds are sitting in a hot PF for between 0-x seconds (where x is the time it takes to complete a grind of your dose; 5-20 second depending on dose and grinder?) plus whatever time it takes to distribute/level/tamp. That would eclipse the time it takes between a bean getting heated through contact with the burrs and it hitting the hot portafilter (which would heat a significant portion of the grinds within a short space of time).

                Also... I think you will find that friction heat of a grinder running at 1380rpm will far exceed 30-ish degrees and the worry would be all about how this additional heat may bake or even burn the coffee.
                Ah, I'm only going by measurements people have quoted of the burrs/grounds immediately following a grind. What burr-face temps might typically be seen in a non-commercial (and out of interest, commercial) application? I have a hard time believing that temps above brew temperature would be reached in a burr grinder, nor that the extra time being exposed to air while heated (a fraction of a second between burr and hot PF) would cause a perceptible difference in taste.

                Do we actually have any science to back this up or is it a concern based on what we ignorantly fear might happen?

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                • #9
                  Regardless of whether there is a difference or not, I like that dragunov is challenging something that is often passed around without any scientific evidence. Be interesting to see what comes out if this one.

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                  • #10
                    Re: Why do we worry about grinders heating grinds to 30°C+...

                    Perhaps the issue is heating of residual oils in the grinder?


                    I grind into a cold (naked) pf personally, but you raise a good point.

                    Comment


                    • #11
                      Quite a few things in the coffee world are thrown around as hard fact without much evidence to back them up. Some of them have come across from the commercial coffee scene and don't really apply in the domestic scene, and I think this is one of them. Unfortunately a lot of these types of issues take quite a bit of time to prove/disprove properly and so a theoretical debate is often as far as it gets. You might be interested in this thread

                      Titan Grinder Project: Does burr heating coffee grounds negatively affect taste of espresso? - Grinders • Home-Barista.com

                      Pete

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                      • #12
                        I sometimes wonder if people who worry about things like this are simply not happy unless they have something obscure to worry about (compulsive worriers) of course compulsive worriers need compulsive listeners, seems both types are thin on the ground here.

                        And they reckon us bean weighers have a problem, this issue beats it in spades.

                        Comment


                        • #13
                          Originally posted by Yelta View Post
                          I sometimes wonder if people who worry about things like this are simply not happy unless they have something obscure to worry about (compulsive worriers) of course compulsive worriers need compulsive listeners, seems both types are thin on the ground here.

                          And they reckon us bean weighers have a problem, this issue beats it in spades.
                          But I don't think there's any problem with people asking the questions in the quest for the ever-elusive "god shot", or for information when considering buying gear that costs a significant amount of coin, or even just for the fun of it, if that's what floats your boat.

                          Pete

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                          • #14
                            Sure, but I can understand the cynical attitude towards a market and consumer base that seems intent on throwing money at problems that may or may not be there.

                            Originally posted by Pete39 View Post
                            Quite a few things in the coffee world are thrown around as hard fact without much evidence to back them up. Some of them have come across from the commercial coffee scene and don't really apply in the domestic scene, and I think this is one of them. Unfortunately a lot of these types of issues take quite a bit of time to prove/disprove properly and so a theoretical debate is often as far as it gets. You might be interested in this thread

                            Titan Grinder Project: Does burr heating coffee grounds negatively affect taste of espresso? - Grinders • Home-Barista.com

                            Pete
                            Cheers, very useful link and lightly points toward what I've been thinking...

                            Originally posted by Yelta View Post
                            I sometimes wonder if people who worry about things like this are simply not happy unless they have something obscure to worry about (compulsive worriers) of course compulsive worriers need compulsive listeners, seems both types are thin on the ground here.

                            And they reckon us bean weighers have a problem, this issue beats it in spades.
                            Actually, I've probably gone off half-cocked here; probably should have asked if anyone here worries about it in a domestic setting (read: takes it into consideration when selecting a grinder). Just because it's something mentioned every now and again on various forum threads and grinder reviews doesn't mean that it's actually a commonly-held belief. @Vinitasse, might I count you as someone who does, or are you speaking purely from a commercial background?

                            I understand that what might be a non-issue for a domestic-duty grinder might be a significant one for a grinder that experiences something like 10% duty-cycle over the course of a day and is has enough metal to retain heat, but personally I'll remain skeptical of the claim until I see something solid.

                            Thing is, people talk about friction, but we're talking sharp metal burrs on soft coffee-beans - the frictional braking isn't enormous.

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                            • #15
                              Re: Why do we worry about grinders heating grinds to 30°C+...

                              How would it be measured?

                              A laser thermometer temp taken on both freshly ground beans, and the burr for comparison?

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