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Why tamping doesnt matter as much as you think

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  • #31
    Re: Why tamping doesnt matter as much as you think

    i have stock BES900 tamp, i just tamp to flatten the coffee so it slots in, and not spilling everywhere...

    I dont really goto town and try to fuse atoms in the basket.

    Light press, squared off, nice and clean. ready to roll

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    • #32
      Re: Why tamping doesnt matter as much as you think

      Originally posted by 1125242439500 link=1332222307/28#28 date=1334206431
      Im saying that the 9 bar of water pressure isnt COMPRESSING the puck with 9 bars. I certainly agree that there is 9 bars of water pressure going through the coffee, but that is not the same as a 9bar tamp.
      Hi Autti - I think we are all arguing the same thing... its just that some imprecise use of language is obfuscating this

      As Randy noted early on, its "apples and oranges unless the water is in the form of ice."

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      • #33
        Re: Why tamping doesnt matter as much as you think

        Noob here - but with my PV Lusso & a fine grind, I can get the flow rate to vary from a thin stream right through to 1 drip per 5 seconds only by varying how hard I tamp. So I do think it makes a big difference and when I drink those shots that took 2-3 minutes to pour you can certainly taste it.
        Im trying to get a feeling for what happens as I tamp - at a certain point you can almost feel the coffee lock down and stop compressing and Im finding best results if I stop just short of that. Or it could be my imagination...

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        • #34
          Re: Why tamping doesnt matter as much as you think

          Originally posted by 072524254A0 link=1332222307/24#24 date=1334119290
          leveled/tamped with her palm
          I hope her hands were clean.

          Comment


          • #35
            Re: Why tamping doesnt matter as much as you think

            One notch on my grinder tends to be the difference between good pour and staller. Id only use a finer setting for supermarket beans. So I mostly adjust the tamp and dose. If I dose a little more and tamp harder, I maintain a good flow rate after my beans have gone stale. If youre tamping down hard but not dosing anymore, so that its tamped lower in the basket, it wont make that much difference because its going to expand upwards into that space and undo much of the harder tamp.

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            • #36
              Re: Why tamping doesnt matter as much as you think

              Warning: This will be a short (or long) lecture.

              As a mineral processing engineers, I deal with a few different process equipment and one of which is filters. Filters works in the principal of pressure difference. The pressure difference is created by applying a vacuum or a pressure force on one side of the filter medium.

              There are two types of filters:
              1. Vacuum filters: The liquid is pulled through (under vacuum) the filter medium, leaving the solids on the
              other side (filter cake)

              2. Pressure filters: The liquid is pushed through (under pressure) the filter medium, leaving the solids on the
              other side (filter cake)

              I think we all agree that our coffee machines are pressure filter so Ill discuss pressure filter instead.

              Key parameters for filters are:
              -
              Particle size
              - Filter medium
              - Feed slurry density
              - Pressure difference
              - Rate of filtration

              Particle size and filter medium is inter-related, and we all know that the our filter basket is fine enough to hold the ground coffee and let the brewed liquid to pass through (the effect of these on filtration rate will be discussed later). Well ignore feed slurry density because its not a factor for our discussion (all use water and ground coffee as the slurry). Pressure difference is created by the espresso machines specific.

              So this is what we were interested in: rate of filtration (or pouring). There are several factors affecting rate:

              1. Resistance of filter medium (basket): is dependent on the size of pores and is impacted by how clean or dirty the filter medium is. when the fine solid particles embedded within the pores of filters,it makes difficult for the liquid to move through the medium. The filter medium resistance is therefore combination of resistance of the filter medium and the embedded particles.

              2. Resistance of filter cake (puck): is dependent upon the filter cake thickness and the amount of voidage (spaces between the particles) in the cake.

              When filtration commences, the filter cake resistance will be zero as initially there will be no cake build-up (i.e. the cake depth will be zero). As filtration proceeds and the cake depth increases, the cake resistance will increase and become the
              predominant source of resistance.

              The voidage or spaces within a cake is related to the size distribution of the solid particles and the particle size. The finer the solid particles, the smaller the spaces between the particles and the higher the cake resistance (due to the particles being packed closer together).

              The higher the resistance, the slower is the rate of pouring. If resistance is too high the moisture level in the final filter cake will increase (wet puck).

              Tamping too hard together with too fine grind size and/or too much ground coffee on filter results in dripping pouring to none at all (Ive tried this).

              In conclusion, tamping does mater up to certain point; it minimise the time required for filter cake formation by pressing and compacting (forced formation) results in evenly distributed and higher resistance initially. Another factors are more important however, such as grind size, height of filter cake (consistent dosing) and pressure difference.

              Open for discussion

              HH

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              • #37
                Re: Why tamping doesnt matter as much as you think

                I dont understand why you would ignore slurry density when it is a dynamic medium and will behave differently at different stages of the extraction.

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                • #38
                  Re: Why tamping doesnt matter as much as you think

                  Originally posted by 1D3C3737302A590 link=1332222307/36#36 date=1338595717
                  I dont understand why you would ignore slurry density when it is a dynamic medium and will behave differently at different stages of the extraction.
                  Because that itself may create separate forum and its not something that we can control (maybe im wrong with this). But i know that density is mass per volume and as temperature increases mass stay the same and volume increases ie. density decreases. However up to certain point, density inside the filter will remain constant due to limited volume, so liquid has to escape somewhere and thus maintain the same density. If water doesnt escape, then it will build up pressure and may cause explosion.

                  Comment


                  • #39
                    Re: Why tamping doesnt matter as much as you think

                    Originally posted by 21283B203A26276721283B203A2627490 link=1332222307/35#35 date=1338595008
                    Warning: This will be a short (or long) lecture.
                    Crikey HH, you obviously have waaaay too much time on your hands. 

                    Comment


                    • #40
                      Re: Why tamping doesnt matter as much as you think

                      HH, I think you might be approaching the topic as though there are constants involved. While there are some, one coffee will behave quite differently to another.

                      Suggest you take a close look at the way most group heads are designed and how they resolve the possibility of explosions. Also recommend to you "espresso coffee the science of quality" by Illy.

                      Comment


                      • #41
                        Re: Why tamping doesnt matter as much as you think

                        Originally posted by 1D3C3737302A590 link=1332222307/39#39 date=1338598760
                        HH, I think you might be approaching the topic as though there are constants involved. While there are some, one coffee will behave quite differently to another.

                        Suggest you take a close look at the way most group heads are designed and how they resolve the possibility of explosions. Also recommend to you "espresso coffee the science of quality" by Illy. 
                        You are absolutely correct, I am just approaching it by bird view, of course there are deeper way to look at it. After all, I am still learning. Will check on the book. Thanks!

                        Originally posted by 003C352D38590 link=1332222307/38#38 date=1338598557
                        Originally posted by 21283B203A26276721283B203A2627490 link=1332222307/35#35 date=1338595008
                        Warning: This will be a short (or long) lecture.
                        Crikey HH, you obviously have waaaay too much time on your hands. 
                        Cant help it, lazy Saturday and reading on CS forum. Cant get any better!

                        Comment


                        • #42
                          Re: Why tamping doesnt matter as much as you think

                          Originally posted by 767F6C776D717030767F6C776D71701E0 link=1332222307/40#40 date=1338599355
                          Will check on the book
                          I think youll love it!!

                          Comment


                          • #43
                            Re: Why tamping doesnt matter as much as you think

                            Originally posted by 77565D5D5A40330 link=1332222307/41#41 date=1338600375
                            Originally posted by 767F6C776D717030767F6C776D71701E0 link=1332222307/40#40 date=1338599355
                            Will check on the book
                            I think youll love it!!
                            Hey thanks for the recommendation Dennis. Was just thinking of buying the ebook yesterday, and it looks like youve convinced me.

                            Now off to do some "light" reading ;D

                            Comment


                            • #44
                              Re: Why tamping doesnt matter as much as you think

                              Originally posted by 4B42514A504C4D0D4B42514A504C4D230 link=1332222307/40#40 date=1338599355
                              Cant help it, lazy Saturday and reading on CS forum. Cant get any better!
                              Fair nuff.

                              Comment


                              • #45
                                Re: Why tamping doesnt matter as much as you think

                                Originally posted by 1024252538510 link=1332222307/28#28 date=1334206431
                                Originally posted by 0E2520204C0 link=1332222307/27#27 date=1334201918
                                Originally posted by 4F7B7A7A670E0 link=1332222307/20#20 date=1334012420
                                My point is that saying a puck is being compressed by 9 bars of pressure is simply false
                                No its not. If your over-pressure valve is set to release pressure at 9 bar (as mine is), and the valve is open during the shot (as it is on my machine - as I can see the water bypass emptying back to the tank), then there must be 9 bar at the coffee puck. If there wasnt 9 bar at the puck the over-pressure valve wouldnt have opened.
                                I not saying there isnt 9 bar of pressure.

                                Im saying that the 9 bar of water pressure isnt COMPRESSING the puck with 9 bars. I certainly agree that there is 9 bars of water pressure going through the coffee, but that is not the same as a 9bar tamp.

                                I will test this on my drill press with a load sensor.

                                I will bet you that 9bar tamp will compress the coffee a lot more than 9 bar water pressure. Ergo you cannot equate water pressure to tamp pressure directly.
                                I think youre getting the idea wrong. The pressurised water at 9 bar is not supposed to compress the puck further. The only thing that should be compressing the puck is the tamper. The whole point of pressurising the brew water is to force it through the little voids between the coffee grounds so that the water comes into contact with every single coffee particle in the puck, and diffuse into the pores on the coffee particles to dissolve the solubles and then flow through the pathways in the voids until it reaches the bottom of the filter basket, through the basket holes and into the cup. So in fact, the 9 bar of water EXPANDS the puck, not COMPRESSING it.

                                Anyway, my opinion is that tamping pressure does affect the extraction to a certain extent, but it is dependent on your dose, distribution and grind size. Its related to the maximum packing density of any packed bed in relation to particle sizes (and of course shapes, but every coffee ground particle will be of slightly different shapes so lets not go there :P) and the extent of the bed expansion during extraction.

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