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  • Puck sticking in new filter basket

    I've been using a Synesso filter basket for some time in my old Duetto, and have just changed to a new Pullman basket in a similar size, possibly slightly bigger. I have made no other changes, the dose is the same, coffee is the same, tamp is the same etc., yet where the old basket used to release the puck intact with just a gentle tap, the new basket requires several hard knocks at which point the puck fractures and comes out in pieces. Each piece is of a similar look and feel to the pucks from the old basket, it just seems that the "stiction" between the coffee and the basket is higher than that which holds the puck together. The shot tastes the same and pulls in much the same time, it just won't knock out cleanly. The other users of the machine have said exactly the same thing (and requested the old basket be returned to service), so it's not just me! I can't see any other differences, the portafilter is removed as soon as it stops dripping and has a tiny amount of wetness on the surface which disappears almost immediately, perhaps slightly more with the new basket but not massively. The new basket is slightly deeper before it "bowls" inwards at the base, so there is slightly more headroom above the coffee, but not a huge amount.

    From a coffee viewpoint it's not an issue - the end result is the same - but from a process viewpoint I now have to wipe out the basket to remove at the very least a thin coating of coffee and at worst "lumps" that are easier to wipe than to keep hammering on the knock-box. The Synesso basket used to knock out perfectly so the next shot could be pulled with zero mucking about.

    So, any ideas why this is happening? Is it related to the slightly larger headroom? Size of holes in the filter? Surface coating or lack of it (i.e. simply age and use)? Or geometry of the basket? Or do I need to start playing with my carefully refined dose to suit the new basket?

    Any thoughts?

  • #2
    I've had similar results going to an IMS basket, curious to see if anyone has any input on what might cause it....

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    • #3
      Go back to the Synesso basket, they have a good reputation.?

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      • #4
        VST user here, new machine and very similar circumstances with the puck always being a tad damp and coming out in pieces. From previous machine and basket, same dose, grinder, technique and coffee didn’t mater. Listened to some of my own advice and did the “5 cent piece” test, increased dose by .4~.5 gram and big difference. Out in one piece and generally clean and dry....maybe worth a look....

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        • #5
          The shape of the basket is different resulting in a different volume of coffee. They are more square at the bottom which will increase water flow and overall extraction, but also the volume.
          Mono has the answer. Do the volume test.

          Results in the cup rule thought. A sloppy puck is secondary to a tasty brew

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          • #6
            So the concept is that the puck expands as it gets wet, until it hits the shower screen which limits its "growth". The increased volume of the new basket allows the dose (which initially has the same weight and, if tamped at the same pressure, the same volume) to expand slightly more, meaning it is slightly softer and wetter, therefore both stickier and more likely to break apart at the end? And increasing the dose until it is big enough to be limited to the same % expansion should result in the same final puck density/hardness/wetness..?

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            • #7
              Originally posted by Warb View Post
              So the concept is that the puck expands as it gets wet, until it hits the shower screen which limits its "growth". The increased volume of the new basket allows the dose (which initially has the same weight and, if tamped at the same pressure, the same volume) to expand slightly more, meaning it is slightly softer and wetter, therefore both stickier and more likely to break apart at the end? And increasing the dose until it is big enough to be limited to the same % expansion should result in the same final puck density/hardness/wetness..?
              Your theory sounds good but honestly I don’t know what the actual physics are I just know it made the difference I was looking for.. I wasn’t getting hung up on it but just couldn’t work out why the mucky pucks......Maybe that with the slightly increased dose size grind can be made ever so slightly more coarse which keeps the shot duration consistent but the larger amount of coffee in the basket is better able to absorb the remaining water.

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              • #8
                Originally posted by Warb View Post
                So the concept is that the puck expands as it gets wet, until it hits the shower screen which limits its "growth". The increased volume of the new basket allows the dose (which initially has the same weight and, if tamped at the same pressure, the same volume) to expand slightly more, meaning it is slightly softer and wetter, therefore both stickier and more likely to break apart at the end? And increasing the dose until it is big enough to be limited to the same % expansion should result in the same final puck density/hardness/wetness..?
                With a normal tamp the puck does not expand during extraction. What most people consider to be puck expansion is in fact the puck getting sucked upwards at the end of the shot when the 3-way valve opens and the pressure in the grouphead/portafilter is suddenly released.


                Java "Sharing science" phile
                Toys! I must have new toys!!!

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                • #9
                  Originally posted by Javaphile View Post

                  With a normal tamp the puck does not expand during extraction. What most people consider to be puck expansion is in fact the puck getting sucked upwards at the end of the shot when the 3-way valve opens and the pressure in the grouphead/portafilter is suddenly released.


                  Java "Sharing science" phile
                  Interesting! I don't think the puck is getting "sucked up" because there is no vacuum above it (unless the three way valve creates one somehow) and it doesn't look like air is entering the bottom of the filter. Given that liquids and solids are not compressable, they can't be expanding either! That means that something else is happening - either there is compressed gas in the puck that expands, or the coffee is absorbing the water in the headspace and expanding like a sponge (like adding water to dehydrated mashed potato!). I suppose, given that some/all of the shot comes out in the form of foam (sorry, ahem, crema), there could be a physical or chemical reaction happening which results in the grains of coffee being filled with gas at the end of the shot, and that gas is expanding when the pressure is released.

                  Now I'm getting off topic, even though it's interesting stuff.

                  However..... if the puck expands, either during or after the shot is pulled (at the release of the three way valve), and for whatever reason, if that expansion is limited in the old basket but not the new one, the result is surely the same - the puck in the new basket is less dense when the idiot pulling the levers (me!) tries to knock it out..! The videos show a huge headspace, when the portafilter is removed those pucks would be under 10mm of water. In my case the "puddle" doesn't even cover 50% of the surface of the puck, so presumably I'm much closer to the shower screen. Those videos seem to show perhaps 15% expansion when pressure is released? So if the puck _just_ touches the screen after expansion (unlike those vids!) then a small change in dose may well make enough difference to alter the final puck consistency.

                  More research tomorrow!!

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                  • #10
                    This blew my mind when I saw it.
                    https://www.youtube.com/watch?v=7A-L00q5a1o

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                    • #11
                      Originally posted by amberale View Post
                      This blew my mind when I saw it.
                      https://www.youtube.com/watch?v=7A-L00q5a1o
                      Which is the same clip linked too in my previous post, just on a different hosting site. There are quite a few more different clips out there as well.


                      Java "Ah the wonders of the interwebby thingy " phile
                      Toys! I must have new toys!!!

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                      • amberale
                        amberale commented
                        Editing a comment
                        Sorry, didn’t notice your linky.
                        I am slightly surprised that that clamouring crowds haven’t demanded a “grown crystal” basket that would out naked a naked portafilter.
                        I mean if we can put a helicopter on Mars....

                      • Javaphile
                        Javaphile commented
                        Editing a comment
                        I hear they're waiting for the orbital factory to start production on that. Micro-gravity crystal growth and all that.


                        Java "Applying to be QC Manager" phile

                    • #12
                      Warb The 'suction' you refer too is generated when the 3-way valve is moved too the 'exhaust' position at the end of the pull. Just prior to to that there is, in a normal/standard shot, 9 bars relative/10 bars absolute of pressure present above the 'screen' in the portafilter and in the grouphead with 0 bars relative/1 bar absolute below the portafilter's 'screen'. At the end of the shot when the 3-way valve is put in the exhaust position that 9/10 bars of high pressure in the portafilter/grouphead is released and the pressure precipitously drops to atmospheric (0/1 bar) pressure.

                      Depending on the machine that pressure can be released very slowly or virtually instantly. Some machines don't have a 3-way valve and the only way that high pressure gets released is to wait for it to slowly work its way through the puck. At the other end of the scale are electronic 3-way valves which open in a fraction of a second. The slower the pressure is released the lower the suction is, and obviously the faster the pressure is released the greater the suction is.

                      Many of the shots pulled in the long video (There are a number of videos on vimeo showing the transparent portafilter being used on different machines.) were at low pressure and light tamps and done on what appears to be an E61 grouphead with a manual 3-way valve. The low 4 bar shot pressure reduces the suction as does the type of grouphead/3-way valve in use. It's not obvious in the linked clip but in others you can literally see the air making its way from the screen up through the puck when the 3-way valve is opened and in some, presumably where the full 9 bars brewing pressure and a heavier tamp was used, you see the entire puck sucked up off of the portafilter's screen with little to no expansion of it at all.


                      Java "Fun with physics" phile
                      Toys! I must have new toys!!!

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                      • #13
                        Given that there is no system for deliberately creating a vacuum, I'm still not sure why there should be any suction at all. Releasing pressure doesn't create vacuum*, nor does it cause the system to drop below atmospheric pressure. I suppose if the drain is 100% full of water, then the momentum of that water might create a low pressure area behind it (i.e. it keeps going at high speed after the pressure is released, similar to cavitation in a pump or propeller), but that would seem unlikely given the very small amounts of water involved. My machine always seems to vent an air (steam?) + water mix when the three way valve is released, and that would seem likely to further reduce the chance of any vacuum being formed - for the split second of potentially negative pressure from the momentum of the water, the air in the headpsace and valve mechanism would expand, the more air the less pressure reduction. In fact, if there is sufficient compressed gas to eject all the water (as seems to be the case in my machine) such that steam/air vents after the water, then the entire concept of the vacuum being created by water moving down the pipe is moot because the water has been ejected whilst there is still positive pressure.

                        *OK, technically if the gas is moving fast enough there is the potential for a vacuum to be formed as the air molecules "overshoot" or generate a Bernoulli effect, but we're not talking about the wing of a plane here, we're talking tiny amounts of air and (relatively) far larger amounts of coffee and water.

                        In any case, the expansion in the video I watched does appear to be "expansion", rather than the entire puck moving upwards. I'll see if I can find some of the other videos and have a look, but I can't see any reason why releasing a three way valve should cause ANY suction, never mind enough to lift a puck that is underwater.

                        [At this point I'm ignoring what seem to be extremely unlikely explanations such as flexing of the filter, water/steam/pressure/temperature vapour pressure interactions etc.]

                        One thing I did notice is that through the shot pull (whilst under pressure), gas bubbles can be seen moving upwards from the top of the puck. Any compressed gas that remains in the puck (either inter or intra coffee particles) _will_ expand when the outside pressure is released, but those gas bubbles, and any other air trapped in the headspace or the valve mechanism will also expand (as mentioned in the previous paragraph) to nullify any vacuum created by fast moving water.

                        I've also always assumed (I remember my lecturers 40odd years ago - "NEVER ASSUME") that coffee expands when wet, and the finer the grind and higher the pressure would (in my mind!) create a greater depth of penetration in any given time, resulting in a larger amount of expansion. This, I've always assumed (!?), was also why my Teddy takes a coarse grind and 18 hours, whilst my espresso's use a fine grind, 9bar of pressure and 25 seconds....a faster rate of movement of water through each coffee particle. Mind you, I remember reading a theory about whether the chemicals ("flavours") in espresso are actually extracted from inside each coffee particle or whether they are simply washed off the surface. But my ageing brain doesn't recall the details!

                        Still, I'll try a slightly larger dose and see what happens!

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                        • #14
                          After a fair degree of experimentation over the last few days, my conclusion is that it is the shape of the basket that causes the problem. Increasing the dose until the shower screen limits the expansion of the puck does reduce/remove the small puddle of excess water from the top which, I suppose, is to be expected. It doesn't significantly change the texture of the puck, because it was only ever the very top that was wet (and thus soft). The puck still breaks up and doesn't come out cleanly. More interesting is that over the last few days, with no changes after the initial dose increase, the pieces of puck that were sticking to the filter reduced and finally disappeared. The only thing I can attribute this to is that either there was a coating on the filter when it was new (a result of the manufacturing process?) or a build-up of coffee oil that makes the base of the puck release from the filter far better than when it was new. I now have a clean filter after the knock-out, but the puck still breaks up.

                          So I did some measuring. The old Synesso basket has a section at the top, approximately 10mm deep, where the sides are "parallel" before they taper inwards to the base which is approximately 52mm across. The new basket, in comparison, has a "parallel sides" depth of more like 18mm, and then tapers only a small amount and is still only fractionally below 60mm across at the base. These are all external measurements, by the way. The interesting part is that the "parallel" section of the Pullman is indeed basically parallel, whilst the Synesso does seem to taper slightly. Forgetting all other factors, this means that the puck in the Synesso basket fits more like a wedge, and is free to drop out of the basket as soon as it has moved even slightly "up the taper". The puck in the new basket, on the other hand, is in contact with the sides of the basket for the majority of its journey out. This can be demonstrated by tapping the handle of the portafilter (rather than the basket section) gently and repeatedly on the knock box, which results in the entire puck slowly emerging from the basket, but not actually releasing and falling out. Eventually the puck will either fall out complete, or split horizontally leaving the bottom half still in the basket (which then comes out with further gentle tapping). This is not possible with the Synesso filter, as soon as the puck releases it just drops out.

                          Whatever the true explanation, the end result is that the coffee tastes great and those annoying lumps of coffee that were sticking to the filter are no longer happening, so removing the need to clean the filter between shots. Having to hit the knock box slightly harder and seeing broken pucks is something I can live with..... at least until I invest in a VST filter to test.....

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