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  • Importance of distance between coffee and shower screen

    Hi,
    I read in other threads on this site that the distance after tamping between the coffee and the shower screen is important.
    Somebody mentioned that when tamping correctly, the compression of the grounds (which I had always assumed changed the resistance to water flow significantly) wasnt as important as the distance to the shower screen.

    I was wondering if somebody could comment on this and explain the effect changing the distance has on the shot. How much variation in distance is noticeable? Is the variation in distance more significant for thermoblock systems than for boiler systems?

    Thanks

  • #2
    Re: Importance of distance between coffee and shower screen

    Originally posted by 607276707C4C66607661130 link=1270604790/0#0 date=1270604790
    Hi,
    I read in other threads on this site that the distance after tamping between the coffee and the shower screen is important.
    Somebody mentioned that when tamping correctly, the compression of the grounds (which I had always assumed changed the resistance to water flow significantly) wasnt as important as the distance to the shower screen.

    I was wondering if somebody could comment on this and explain the effect changing the distance has on the shot. How much variation in distance is noticeable? Is the variation in distance more significant for thermoblock systems than for boiler systems?

    Thanks
    It is simple physics BUT often miss understood.

    There are of course so many variables. that there is no single response that is 100% correct.

    1: Coffee needs to be compressed to a value defined by and wrt the grind size and bean type; to attempt to manage the flow of water at the correct temp at the desired rate.

    Outcome = A good cup if ya get it right.

    How is the water flow managed = Pump / Tamp / Basket type (single / double floor)

    2: Coffee expands when wet -

    is it an instant even expansion = NO

    pre-infusion has an effect = YES

    Temp has an effect = yes

    3: If packed to low and water through teh shower screen fast etc then the top layer can get all mucky.

    Does this affect teh cup = Yes and no BUT has a major impact on cleaning and dumping the used grinds.

    4: If packed right... The beans swell and by the end of teh run, are firm / touching the shower screen and will leave a slight impression in the puck and should be reasonable dry..

    With the expansion of the beans.. It also means the level of compactness changes.

    So if ya needed x to get a great shot. You would tamp at X + Y where Y = the losses due to expansion.


    There are other factors here as to impacting on how it dries etc... As stated before lots of variables and physics taking place.

    5: If ya Updose.....

    Then in addition to ya tamp; slight pressure is now being applied by the shower screen.

    Thus in effect having an impact on that value of Y. Further more as teh coffee has no where to expand it in effect adds to the compression. An inverse reaction.

    6: If ya OVERDOSE...

    Then ya start to really complicate matters and the pressures involved with expansion etc and water flow realy get interesting.

    Thus some people grind courser and compensate by OVERDOSING..

    What does this do... Basic logic sates that if you apply excessive pressure to any thing.. Sooner or later things will suffer from stress.

    As per shower screens... Meant to diffuse teh water flow to provide an even wetness and path way. When ya always OVERDOSING.. They will suffer over time. But what is really interesting is the excess amount of Oils and gunk that gets forced back-into the system.

    So what the trick...

    Grind / Tamp and dose correctly and OVERDOSING is NOT required.


    Any mathematicians here ? Would make a great formula and then some one can do coffee by numbers; excluding beans type / freshness / grind consistency and any number of other variables that come into play.


    Coffee is so simple is it not

    Thats why Autos can not pull those great shots day in and day out.. Many of the variables such as tamp and dose can be managed... But the variables are always there









    Comment


    • #3
      Re: Importance of distance between coffee and shower screen

      Thanks,
      Informative response.

      To confirm my ignorance:
      If I use the same grind, dose and tamp in both a single and double basket I get different shots. Is this just due to the different head space and hence pressure difference? Or do some of the other factors you mention come into play?

      Comment


      • #4
        Re: Importance of distance between coffee and shower screen

        Originally posted by 293B3F3935052F293F285A0 link=1270604790/2#2 date=1270609532
        Thanks,
        Informative response.

        To confirm my ignorance:
        If I use the same grind, dose and tamp in both a single and double basket I get different shots. Is this just due to the different head space and hence pressure difference? Or do some of the other factors you mention come into play?
        All of the above...

        Every basket has different properties. Thus the depth of the basket Vs length of time for coffee to pass through etc.

        Just look at a pod and how thin they are.. Err 30 or 60 ml of coffee after 30 seconds.. Work it out.

        Comment


        • #5
          Re: Importance of distance between coffee and shower screen

          On my personal coffee making routine I have found this tamp depth style makes the best coffee for me
          The ideal puck to screen space is approx 1mm or less but not touching
          Max 2mm

          Trial and error will determine the depth you need to tamp for correct head space (for my machine its 8mm) then use that as a future reference

          KK

          Comment


          • #6
            Re: Importance of distance between coffee and shower screen

            > Every basket has different properties.

            How about if we take two baskets, same material, same hole size/pattern, same diameter, just different depths. We fill them with the same grind, dose, tamp of coffee. We now have the same depth of coffee, the only difference being the distance from the shower screen when the portafilter is attached.

            How does that small amount of extra space above the coffee make such a difference to flow rate? (Physics anybody?)

            Comment


            • #7
              Re: Importance of distance between coffee and shower screen

              Originally posted by 24363234380822243225570 link=1270604790/5#5 date=1270613993
              > Every basket has different properties.

              How about if we take two baskets, same material, same hole size/pattern, same diameter, just different depths. We fill them with the same grind, dose, tamp of coffee. We now have the same depth of coffee, the only difference being the distance from the shower screen when the portafilter is attached.

              How does that small amount of extra space above the coffee make such a difference to flow rate? (Physics anybody?)  
              All explained in my first post.  If ya dont understand it ...

              Go an study some more and get a better understanding as the the physic and properties of all the variables.. Then ya can come back and tell others; that might care.

              In the mean time.. This old billy goat gruff is off for a nanna nap and to escape the trolls.

              Comment


              • #8
                Re: Importance of distance between coffee and shower screen

                Originally posted by 2A383C3A36062C2A3C2B590 link=1270604790/5#5 date=1270613993
                > Every basket has different properties.

                How about if we take two baskets, same material, same hole size/pattern, same diameter, just different depths. We fill them with the same grind, dose, tamp of coffee. We now have the same depth of coffee, the only difference being the distance from the shower screen when the portafilter is attached.

                How does that small amount of extra space above the coffee make such a difference to flow rate? (Physics anybody?)
                The head space and tamp depth is your accurate guide to ones particular machine

                If you change to a smaller basket you need to have less coffee to clear your screen or you risk over-dosing

                Conversely
                If you have a larger basket you will need to add more coffee or you risk under-dosing

                No mater what basket one uses the clearance should be as I described above in post #4

                KK

                Comment


                • #9
                  Re: Importance of distance between coffee and shower screen

                  So Im now starting to get the impression that the change in pressure produced as the grounds swell against the shower screen is an important factor. Otherwise why not just have deep baskets where the swollen grounds never touch the screen.

                  And I did read above:
                  >the top layer can get all mucky.
                  >Does this affect the cup = Yes and no
                  but am not sure of its significance

                  Comment


                  • #10
                    Re: Importance of distance between coffee and shower screen

                    Originally posted by 44565254586842445245370 link=1270604790/8#8 date=1270617474
                    So Im now starting to get the impression that the change in pressure produced as the grounds swell against the shower screen is an important factor. Otherwise why not just have deep baskets where the swollen grounds never touch the screen.
                    Water under pressure will hit the top of the tamped coffee and cause channelling

                    This is made worse by two other factors
                    1] Height of the water drop
                    2] Filling & flooding of the cavity with water will weaken the puck

                    Originally posted by 44565254586842445245370 link=1270604790/0#0 date=1270604790
                    I had always assumed changed the resistance to water flow significantly) wasnt as important as the distance to the shower screen.
                    It is important
                    To make good coffee you need resistance at a specific time flow rate @ 20 to 30 seconds for 30 ml of extracted coffee [single] 60 ml[double]

                    This is archived with
                    1] Correct puck depth and head clearance
                    2] Grind setting
                    3] Tamp pressure

                    Important note
                    Ambient weather conditions such as humidity & age of beans will affect ones technique
                    A good operator will make adjustments to grind and tamp pressure several times a day to achieve the ideal resistance to flow rate to keep everything in the sweet zone

                    Use the information I have given you well as its 100 years old

                    If you want to experiment on other ways you are welcome to do so and report your findings

                    KK




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