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  • Testing retention properly

    For a while I was thinking how to test retention properly.
    What do you think about this technique?
    1. After the grinder was used I remove the hopper and remove all beans I can reach with tweezers - I hope I can get all "unground" ones without shaking and tilting the grinder.
    2. Put grinder cleaning pellets into the grinder.
    3. Start the grinder and stop it as soon as I see white particles took over black particles
    4. Weight that ground coffee

    I know for a some time I will get a mix of coffee with pellets. But if I stop in time I will get some white particles out while I still have some coffee particles in the grinder too. So I assume it will even them out.

    If it sounds reasonable I need to source small amount of grinder cleaning particles - I am not sure I need 400g of it.

    Initially I though I could use green beans instead of cleaning pellets but people are saying green beans might damage the grinder (I suspected it so that's why I googled it in the first place).

  • #2
    Sounds like it would work. Not sure why you would need to pull whole beans out of the grinder though. Perhaps its the curse of assumption but I thought they would have all bean (sorry, could not help myself) ground.

    With the tweezer thing, you can achieve the same result if you have both light and dark beans at your disposal. I run very light roast bean through and flush out whatever retained grounds was in grinder. Then I run a very dark roast through and stop almost immediately i.e. when I see the light roasted beans have been pushed out and dark grinds are staring to emerge.

    I then separate any dark roasted grinds.

    Then weigh the light coloured grinds. Of course it's not precise because there is still a few darker grinds in what I weigh but I estimate it's close to within a range of 0.2 grams and 0.5 grams. And really, retention will vary a bit from grind to grind I suspect.

    I did this for the Mahlkonig X54 and reckon retention was 1.5g max.

    What's the grinder you are wanting to test?

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    • #3
      I have Eureka Specialita.
      Light roast vs dark roast - I am afraid it won't be that obvious so it will be harder to find the point to stop.

      The reason why I think pulling beans out of the grinder - I am not talking about "single dose" scenario. I have hopper with some beans. Even if I remove the hopper I still have whole beans are sitting on top of the burr. I call "retention" the ground coffee sitting in the burr and around, I don't count whole beans and I want to remove them from the equation (with tweezers ).

      Edit: What do you think about using oats as a "different colour substance"?
      Last edited by gerbi; 6 September 2021, 03:06 AM.

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      • #4
        I would pull a shot, weigh dose in/out and time.
        make a big grinder change, probably coarser
        keep pulling shots tracking the previously mentioned numbers until it settles down again.
        total of ground coffee until change settles in = grounds retention

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        • #5
          Originally posted by gerbi View Post

          I know for a some time I will get a mix of coffee with pellets. But if I stop in time I will get some white particles out while I still have some coffee particles in the grinder too. So I assume it will even them out.
          This would only work if the retention of the white particles is identical to that of coffee. I am not sure if that's the case.

          For an easily available contrast particle you could try barley: at the maltings lab we used to grind unmalted barley with a Mazzer Mini to protect the very expensive Muhler Diag disc mill used for malt (which is much more friable than barley because of the polysaccharide modifications during the malting process).

          We must have put about a tonne of barley per year through the Mazzer without damage.

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          • #6
            Not sure about this method - the problem with the true retention is there are nooks n crannies that get filled with coffee that essentially never move (or move so little it won't make any real difference) so these grinds aren't truly 'retained'.

            I think the method of light & dark roast mentioned above would work to get a general idea as would sweeping the grind path to remove the likely retained coffee. This would probably be accurate to within 0.1-0.2g or so range. More than enough to give you a pretty good idea.

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            • #7
              Originally posted by WhatEverBeansNecessary View Post
              Not sure about this method - the problem with the true retention is there are nooks n crannies that get filled with coffee that essentially never move (or move so little it won't make any real difference) so these grinds aren't truly 'retained'.

              I think the method of light & dark roast mentioned above would work to get a general idea as would sweeping the grind path to remove the likely retained coffee. This would probably be accurate to within 0.1-0.2g or so range. More than enough to give you a pretty good idea.
              I think there is some terminology confusion.
              Some people call "retention" whatever is retain by the brand new/clean grinder.
              If I sweep the grinder I will get all ground coffee which would normally stay inside forever.
              I am no interested in this.

              Some people (and youtube channels) call retention waterer fits under your hopper shut off valve.
              I am not interested in this either

              What I care about is that stale ground coffee in the burrs and shoot which will be "pushed out" by the next fresh doze.
              So if the next fresh doze is in a different colour - I will see how much of the previous doze was still hiding in burrs.



              I like the idea of using barley.

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              • #8
                Sounds like you want the "silicone bellows" that somebody makes. A quick puff while grinder running to expel the retained grinds through chute. Not high pressure so wont dislodge the static grinds, and little risk of forcing grinds into the machine internals.

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                • #9
                  Not all the stale grounds are pushed out by the next dose. Depending on the grinder you might get 60% with the first dose, 20% with the next dose, 10% with the next and so on.

                  Comment


                  • #10
                    Originally posted by level3ninja View Post
                    Not all the stale grounds are pushed out by the next dose. Depending on the grinder you might get 60% with the first dose, 20% with the next dose, 10% with the next and so on.
                    Yes, I understand that.
                    This test would show how long old ground coffee is staying in the grinder too.
                    The idea is to grind to the point where the amount of white particles and dark particles are equal.
                    This would mean that 50% of old grind is pushed out and while I still have some old particles still in the grinder I have some new out. So the amount of "replaceable" ground coffee will be the amount of the mix delivery up to that point.

                    What do you think about barley?
                    Is it safe for the grinder?

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                    • #11
                      Maybe a dumb question, but what will you do with the information once you have it?

                      Comment


                      • WhatEverBeansNecessary
                        WhatEverBeansNecessary commented
                        Editing a comment
                        Agree - it's a nice to have. But realistically once you get the info it wont change anything. All grinders (even the 'zero' retention grinders) will retain something, it's just a matter of to what degree does it impact taste.
                        Zero retention grinders with 0.2g retained are probably not going to impact flavour to a degree 99% of drinkers will notice.
                        7g from a large commercial grinder probably will impact if left for a number of hours. In this case just purge a little bit and away you go.

                      • sacsnob
                        sacsnob commented
                        Editing a comment
                        7g purge * 30 = 210g/mth, is not a negligible amount for many people. esp for people like me who only consume 1-2 cups/day.

                      • WhatEverBeansNecessary
                        WhatEverBeansNecessary commented
                        Editing a comment
                        Agree. 7g will have an impact on taste and the hip pocket wasting beans like that. Also likely need to purge more than 7g to get out the 7g retained.
                        But in a busy cafe doing dozen or more shots an hour, it's no big deal taste wise.

                        Many folk who have large commercial grinders sweep out the grind path to lessen retention.

                    • #12
                      Thread could also be renamed Tasting Retention. At what point can you distinguish the difference?

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                      • WhatEverBeansNecessary
                        WhatEverBeansNecessary commented
                        Editing a comment
                        Far more meaningful application of retention testing. At what point does it actually make a difference to taste?

                    • #13
                      Originally posted by Caffeinator View Post
                      Thread could also be renamed Tasting Retention. At what point can you distinguish the difference?
                      Testing taste is beyond my expertise.

                      With Breville Smart Grinder it was a noticeable difference in extraction speed between morning shot without purge and the one with a purge. So I believed the retention I am talking about was noticeable. Again, I am technical person, not talking about taste here.

                      For Eureka Specialita the purge affect is less significant.

                      Comment


                      • #14
                        Originally posted by saeco_user View Post
                        Maybe a dumb question, but what will you do with the information once you have it?
                        I was thinking about sharing results here.
                        Although quietly enjoying my achievement is an option too.

                        On a serious side: this won't change much for my workflow. I might purge more or purge less or stop doing it depends on what I find.
                        Also I might try to compare Eureka Specialita to Eureka Mignon XL to see how much marketing BS is in Eureka's ELR (Extremely Low Retention) System.

                        But you are right - it might be interesting for some coffee snobs. But most people don't care like they don't care about speed of light in vacuum vs speed of light in the air.

                        Comment


                        • saeco_user
                          saeco_user commented
                          Editing a comment
                          I also wonder about how much coffee you'll waste doing the testing (assuming you won't drink it with barley contamination - then again you might invent a new and novel beverage)? The best you'll get is an average measure of retained grinds per shot. This will need to be calculated over quite a number of shots as different beans, roast levels, humidity levels etc, will all impact the amount of retention (ie some days the chute will clog up and on others it will mostly empty). From shot to shot the amount is unlikely to be very consistent.

                      • #15
                        Coffee waste - I am ready for this sacrifice. I wasn't going to drink barley infused espresso originally... But I might give it a shot.

                        Complexity in climate conditions - absolutely. Ideally this experiment should be done in some weather chamber repeated for various combinations of temperature, humidity and altitude (pressure). If I manage to pull it off I might publish it in some scientific magazines too.
                        But I am not going to do it - for this I am not ready yet.

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