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Thread: Why do we worry about grinders heating grinds to 30C+...

  1. #1
    Senior Member Dragunov21's Avatar
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    Why do we worry about grinders heating grinds to 30C+...

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    ... When the next thing we do is put the grinds in a 80C+ PF for a reasonably extended period before they see a drop of water?

    Serious question. Have I missed something?

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    Senior Member Vinitasse's Avatar
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    Quote Originally Posted by Dragunov21 View Post
    ... When the next thing we do is put the grinds in a 80C+ 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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    Re: Why do we worry about grinders heating grinds to 30C+...

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

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

    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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    Senior Member Vinitasse's Avatar
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    Quote 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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    Why do we worry about grinders heating grinds to 30C+...

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

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    Senior Member Dragunov21's Avatar
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    Quote 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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    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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    Re: Why do we worry about grinders heating grinds to 30C+...

    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.

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    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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    Senior Member Yelta's Avatar
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    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.
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    Quote 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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    Senior Member Dragunov21's Avatar
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    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.

    Quote 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...

    Quote 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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    Re: Why do we worry about grinders heating grinds to 30C+...

    How would it be measured?

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

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    Even if you quantified the temperature difference, you need to know when that quantity becomes significant in terms of taste. So probably the best place to start would be some blind tasting with a cool grinder and the same model of grinder that has been operating for long enough to heat up the burrs.

    Pete

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    Senior Member Dragunov21's Avatar
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    I'm assuming you mean infrared, and yeah. Still wouldn't give you an ideal/precise measurement, but I'm thinking if you ran it up to whatever your maximum working temp was likely to be then removed the hopper and fed beans in manually while pointing it at the burr interface as far down as was visible then your max temp reading might be close to the max temp grinds would see.

    Unfortunately, it could only prove that grinds do get hot or might get hot, not that they do not, as the finer burr-face (where presumably the most heat is generated) is obscured.

    Quote Originally Posted by Pete39 View Post
    Even if you quantified the temperature difference, you need to know when that quantity becomes significant in terms of taste.
    Not if you can prove that the heating effect on grinds in the grinder is eclipsed by the heating effect on grinds into a hot PF, which seems to be everyone's advice to prevent dropping the grouphead (and therefore brew) temp.

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    Quote Originally Posted by Dragunov21 View Post
    Not if you can prove that the heating effect on grinds in the grinder is eclipsed by the heating effect on grinds into a hot PF, which seems to be everyone's advice to prevent dropping the grouphead (and therefore brew) temp.
    But we don't know if heat applied during grinding has the same affect as heat applied by a hot pf (for example, a large proportion of the dry coffee in the pf will be insulated from the hot basket for some time where as the heat applied during grinding will probably be more uniform). And we don't know how sensitive espresso taste/texture is to a change in grounds temperature. That is, at what temperature difference is one temp "eclipsed" by the other? We don't need to concern ourselves with any of this if we just compare shots from a "cold" and "hot grinder". The if we find a significant effect, we can design other experiments to determine the cause.
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    Why do we worry about grinders heating grinds to 30C+...

    A couple of thoughts on this:

    The ground beans, at the point of exiting the burrs, are surely well in excess of 30 degrees - given that a typical cafe has an ambient temp of say 22-24 degrees, then the beans are packed together in the grinder with a kilo or two of weight on top of each bean, add in the movement of beans as they approach the burrs, then the actual friction when being ground.

    Very happy to read otherwise, but I'd be surprised if this doesn't increase the temp, at the point of exiting the burrs, to 50-60 degrees, or even higher.

    Second thought, as hot as your PF will be, the basket itself is a much thinner material and mostly not in contact with the hotter PF, so I'd expect the temp of the basket so be significantly less than the PF itself.

    Much of this is easy to test...it's the weekend coming up, I sense a bit of home experimentation with spouted and naked PFs.
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  20. #20
    Senior Member Dragunov21's Avatar
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    I'm trying to stay away from subjective measures as far as possible. The only issues here are degradation caused by absolute temp of grinds, and degradation caused by oxidation (combination of time exposed to air and heat during that time).

    If you can prove that grinding into a hot PF causes far greater exposure to heat+air and absolute temp of grinds than does the grinding itself, then you may consider grind temperature a moot point until people stop grinding into hot PFs and may logically advise against giving weight to grind temp considerations when selecting a grinder. This is true regardless of what effect you may subjectively detect between grinds kept cool and grinds heated, because all you're doing is proving that the majority of degradation, detectable or not, does not occur at the grinder.

  21. #21
    Senior Member Dragunov21's Avatar
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    Quote Originally Posted by Jonathon View Post
    The ground beans, at the point of exiting the burrs, are surely well in excess of 30 degrees - given that a typical cafe has an ambient temp of say 22-24 degrees, then the beans are packed together in the grinder with a kilo or two of weight on top of each bean, add in the movement of beans as they approach the burrs, then the actual friction when being ground.
    This (making assumptions) is what I'm hoping to avoid. There may be a great deal of frictional heat when grinding or very little, given a well-designed, sharp burrset.

    As for the PF basket, it will have a lower thermal mass and faster dissipation, but it's still drawing heat from a heavy mass of brass sitting at (for my Gaggia) 92.

    I'll see if I can pinch an IR thermometer from work and get around to getting some measurements for y'all.

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

    Serious question. Have I missed something?
    if the coffee tastes good, there is nothing to worry about ....

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    I'm trying to stick to the issue you raised in your OP - the reason people worry about grinders that heat the grounds is that it might have a bad affect on the espresso. Unless you can taste the effect of the possible degradation you refer to, it is insignificant. My current coffee tastes nice (to me anyway) brewed at either 93C or 94C or even 95 - I don't think I can detect a difference. My previous roast had sour notes at 92, nice at 93 and burnt flavors started appearing at 94. So even though I know brew temperature affects taste, a degree here or there with my current blend won't matter. but I don't know about coffee grounds, so my first test would be taste. Taste tests can be made objective (for example, triangular tests with enough samples).

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    Quote Originally Posted by opus2 View Post
    if the coffee tastes good, there is nothing to worry about ....
    I think the point is not "does it taste good?", but "could it taste better?"

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    And how many angels can dance on the head of a pin ???

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    Senior Member Dragunov21's Avatar
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    Quote Originally Posted by leograyson View Post
    And how many angels can dance on the head of a pin ???
    Cute, but I'm not asking because I want to know if I'm making coffee that's only 99% as tasty as it can be.

    I'm asking because I think that the hobby/profession of coffee is in need of a paradigm shift away from black magic toward science and evidence-based claims.

    As someone with a taste for high-end audio I'm all too aware of how mystique can be used to hide poor performance/value or convince consumers that they need to spend more money tweaking their setups. With high-end audio, once you reach a certain point the engineering becomes so esoteric and the results so subjective that it's impossible to prove a claim true or false.

    I think that coffee has not reached that level of transparency yet.
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    I'm not interested in how many angles can dance on the end of a pin, but if I was, I'd first want to know if it had an affect on anything. Then I might try to measure how many there were.

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    Quote Originally Posted by Pete39 View Post
    I think the point is not "does it taste good?", but "could it taste better?"
    I don't have a reference taste, it can taste different but that does not mean it is bad ....
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    Quote Originally Posted by Dragunov21 View Post
    Cute, but I'm not asking because I want to know if I'm making coffee that's only 99% as tasty as it can be.

    I'm asking because I think that the hobby/profession of coffee is in need of a paradigm shift away from black magic toward science and evidence-based claims.

    As someone with a taste for high-end audio I'm all too aware of how mystique can be used to hide poor performance/value or convince consumers that they need to spend more money tweaking their setups. With high-end audio, once you reach a certain point the engineering becomes so esoteric and the results so subjective that it's impossible to prove a claim true or false.

    I think that coffee has not reached that level of transparency yet.
    I would say this shift is underway, Machines are coming with shot timers, baristas are weighing doses, using refractometers and discussing brew ratio's etc.

    The nice thing is that the more we know things rather the "feel" things the easier it is to pass on the knowlege and standards can rise across the board.

  30. #30
    Senior Member yabba's Avatar
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    Quote 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.
    Yelta,

    You sound like your bean weighing obsession was worrying you. Sorry mate, looks like you have both...
    Cheers Yabba

  31. #31
    Senior Member GrahamK's Avatar
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    According to "Espresso Coffee The Science of quality" by Illy & co, there are a blend of acids that are very viscous at room temp, but start becoming fluid at around 40C. blah blah. Bottom line is it can affect the hydraulic resistance of the cake.

    "Overheating on grinding may thus be responsible for erratic percolation behaviour when brewing espresso. It must be stressed therefore that temperature control in grinding equipment is one of the main requirements to obtain a powder fit for preparing consistently perfect espresso cups."

    Not sure how much this would effect the home brewer making 1 or 2, but possibly important for a busy Caf.

    Coffee Oil Viscosity table
    T(C) Viscosity (mPa s)
    0 Solid
    20 70.6
    50 22.4
    92 7.8


    GrahamK
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  32. #32
    Senior Member Barry O'Speedwagon's Avatar
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    Quote Originally Posted by Pete39 View Post
    I'm not interested in how many angles can dance on the end of a pin, but if I was, I'd first want to know if it had an affect on anything.
    It depends whether the angles are obtuse.
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  33. #33
    Senior Member Vinitasse's Avatar
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    Quote Originally Posted by Dragunov21 View Post
    @Vinitasse, might I count you as someone who does, or are you speaking purely from a commercial background?
    It's important for me to know how my coffee comes across to my customers so even when making coffee at home I use commercial equipment and if the potentially harmful impact grinder heat can have on the finished product is important to my clientele then it's important to me as well.

    That's where I'm coming from.
    Last edited by Vinitasse; 3rd May 2013 at 04:03 PM.

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    On a related note, I found an interesting (old) article today from The Food Lab at Serious Eats about cooking pasta

    The Food Lab: A New Way to Cook Pasta? | Serious Eats

    The gist of it is that all of the old folklore about having to cook the pasta in a big pot of fast-boiling water is essentially just myth. As long as it's dried pasta, the author finds that you can cook it in a small pot of water starting from cold, bringing it to the boil, and then turning the heat off, and the result is just the same. There are only a couple of critical things that matter. It's an interesting read, and reading this reminded me very much of all the coffee-lore. I definitely appreciate where Dragunov is coming from, in that a more scientific understanding of coffee will lead to all round better, more reliable results- and would also be interesting in itself.

  35. #35
    Senior Member GrahamK's Avatar
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    I suggest the science does exist, such as published by Andrea Illy and Rinantonia Viani, and also readily available. Not particularly easy to read though

    Graham
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    Senior Member chokkidog's Avatar
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    I have no intention of buying into the discussion but was prompted to stick my thermocouple where it belongs.........

    Ambient temp.....................................19.8C
    Coffee puck after dose and tamp............24.6C
    Coffee puck + 1 min............................26.2C

    Grinder..................................Mazzer Robur-e.
    Hot naked pf.
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  37. #37
    Senior Member Dragunov21's Avatar
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    Quote Originally Posted by Vinitasse View Post
    It's important for me to know how my coffee comes across to my customers so even when making coffee at home I use commercial equipment and if the potentially harmful impact grinder heat can have on the finished product is important to my clientele then it's important to me as well.

    That's where I'm coming from.
    It's not so much the equipment as the duty-cycle that interests me, but cheers.

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

    Quote Originally Posted by chokkidog View Post
    I have no intention of buying into the discussion but was prompted to stick my thermocouple where it belongs.........

    Ambient temp.....................................19.8C
    Coffee puck after dose and tamp............24.6C
    Coffee puck + 1 min............................26.2C

    Grinder..................................Mazzer Robur-e.
    Hot naked pf.
    Very interesting. Not wishing to labour the point, but with your Robur-e the whole dose would have come out in about 4 seconds tops? So the coffee had a whole lot less time in contact with the hot section compared to 25 second home grinder?

  39. #39
    Senior Member chokkidog's Avatar
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    Yeah, which is why I only measured the 4th dose.

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    Senior Member Dragunov21's Avatar
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    Quote Originally Posted by chokkidog View Post
    Yeah, which is why I only measured the 4th dose.
    Out of interest, where was your TC bead? I guarantee the grounds closer to the metal parts will heat up more than 5 from room temp but I've no idea how far into the mass the heat will transfer in the short period of time (from a thermal conductivity perspective) it has before brewing.



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