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Does the puck swell?

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  • Does the puck swell?

    Rather than hijack the other thread, I’ve started a new one.

    The photos below are this morning’s puck. The BEFORE photo is taken after I've inserted the PF into the group head and then removed it to check it wasn't touching the screen.

    I've pulled the shot and taken the AFTER photo. You can clearly see the indentations of the screen in the puck.

    So in my reptilian brain, I'm concluding the puck is swelling. The alternatives are screen lowering (not likely) or the puck being sucked up which is a possibility but end result is the same, dirty/oily screen.

    Not sure if it makes a difference but I'm using a BES920 with smart grinder pro, beans roasted about 10 days ago.

    FYI, it’s a new roast which I’m still dialling in.

    Penny for your thoughts…

    EDIT: btw one implication is dosing level when using the 5c coin trick. Do you check for coin impression before or after pulling the shot?
    Click image for larger version

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  • #2
    People have tried to help, you now need to do some personal research.

    FWIW the 5 cent coin is only used to establish your dose level prior to pulling the shot, its removed before the coffee is extracted.

    Google is a handy search engine!

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    • #3
      This was answered in the other thread. Puck swells but not because of the brewing process. Puck swells when pressure is released.

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      • #4
        There's a youtube vid somewhere of the clear portafilter Java mentions showing expansion only after pressure relief. It makes total sense too - a 30 pound tamp is about 7 psi of compression. I can't imagine 130 psi of water pressure is going to allow much swelling during extraction.

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        • #5
          Yes, being a BES920 does make a difference. The inverted solenoid valve creates a vacuum on the puck more so than in other solenoid operated groups. You may find that the puck sometimes sticks to the shower screen, that's why.

          On my BES900, this effect isn't present as I use a VST basket. It must be something to do with the stock basket construction as well, perhaps as it tapers whereas my VST is straight walled makes some sort of difference.

          The other day I removed the group handle as soon as I stopped the shot (within 1 second of stopping) and the puck was risen above the rim of the basket.
          This seems to me that the primary expansion, at least upwards, is when the solenoid opens and releases the pressure.

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          • #6
            Originally posted by simonko View Post
            There's a youtube vid somewhere of the clear portafilter Java mentions showing expansion only after pressure relief. It makes total sense too - a 30 pound tamp is about 7 psi of compression. I can't imagine 130 psi of water pressure is going to allow much swelling during extraction.
            Great, so the puck does swell, just not during extraction which is what I originally thought.

            And your logic seems to make sense to me too. Thanks for that.

            Edit: Missed your post Noidle. I don't normally get sticking now days unless I over fill the basket but it's good to know the cause. This latest batch is swelling/expanding/rising a lot more than the previous batch though not sure why. Same beans, roast profile and dosage, just different age (and grind size). Tomorrow I'll just cut back a bit. I used to be a lot more AR about dosage but now as long as it tastes good and doesn't hit the screen I'm happy.

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            • #7
              Originally posted by Yelta View Post
              People have tried to help, you now need to do some personal research.

              FWIW the 5 cent coin is only used to establish your dose level prior to pulling the shot, its removed before the coffee is extracted.

              Google is a handy search engine!
              Man, this guy has been told twice in the other thread and still he asked again, there's just no hope for some!

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              • #8
                Sorry my bad. I went through the other thread and saw what I missed.

                I tend to skim read now days and occasionally miss stuff.

                Apologies.

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