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  • Chanelling?

    This really should have some photos attached, but meh, the pucks are in the bin...

    With the new VBM I received 2kg of beans, and its taken just on 2 weeks to plough through them all. (No I didnt drink it all)

    In that time, and particularly moreso as the beans aged, I notice more and/or larger defects in the top of the used grounds. Usually its a pit, maybe 5mm or so wide, with a smaller hole at the centre. Generally at or near the edge of the puck. Seems to fit the usual description of channelling. However if I knock out the puck theres no sign of defects at the bottom, and if I break it in half the pits dont seem to be any deeper than what can be seen from the top.

    So is this worth worrying about? I am usually pretty careful about dosing and distributing (Stockfleth), my tamper is well undersize though. I dont really notice any dramatic problems in the pour or in the cup, but than again Im no expert...

  • #2
    Re: Chanelling?

    A little hard to diagnose, Matt, but sometimes these holes are left by part of the puck separating and sticking to the shower screen.

    A quick look at the screen will confirm if that is the case."Way undersized" tampers will not compress the puck at the edge, leaving that circumference prone to channelling.

    --Robusto

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    • #3
      Re: Chanelling?

      Originally posted by robusto link=1185861944/0#1 date=1185865786

      "Way undersized" tampers will not compress the puck at the edge, leaving that circumference prone to channelling.

      --Robusto

      Unless multiple tamps (e.g. NSEW) are used.... the edge will now be compressed but each tamp will possibly fracture the puck- and this fracture could be anywhere within the puck.... and thats where you will get channelling.

      You should tamp once - and once only if you want to avoid possible fracture lines.

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      • #4
        Re: Chanelling?

        No corresponding grounds are left on the showerscreen.

        I only tamp once, multiple tamps suffer more issues I find. Ultimately I want to get a properly fitted tamper, and a naked PF would be nice to really know whats going on too.

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        • #5
          Re: Chanelling?

          Hi Matt,

          My $0.02; anything that might be referred to as "channeling" is utterly irrelevant if it doesnt have a result in the cup. I think that it is jumping to conclusions to presume that you have been getting channeling unless (a) you have seen the espresso stream suddenly lighten in colour, thin out in texture and increase in flow rate and (b) the resultant espresso has a distinct searing acidity and watery texture. You need to observe both together because either can be accounted for separately. (a) is a common characteristic of some espresso machines (one particular prosumer machine springs to mind) and (b) can simply be a result of under-dosing.

          Whether or not you have been experiencing channeling, your modus operandi should be the same - if you dont like the result in the cup, change one variable at a time until you get a result that you do like.

          Frankly, I find it hard to believe that channeling would be a common occurrence on most machines with a pressure ramp-up that make it take more than about six seconds before you see the first drops. Ill give two experiences that make me suspicious of this "sky is falling" trend. First, yesterday at work I put a single origin Kenyan Gallia on for cappuccino, seeing as James Hoffmann used something similar to win the WBC last week. I took the opportunity to experiment with a very low dose to accentuate the acidity. I ground, struck off level and tamped, using the bottomless portafilter for kicks. Every time, the pour looked the same - several streams coming out to start off with, converging into a central stream within the first few seconds. One would have thought that if anything would be prone to channeling it would be down-dosed shots. The second example would be seeing Andrew tamp with the palm of his hand and pull a perfect shot at Maling Room. Finally, if more examples are needed, Im sure that people have done numerous experiments with not tamping at all and have, at least occasionally, gotten away with it.

          The Vibiemmes that I used the other week at Aroma all seemed to have quite long preinfusion times, so Im sure that youre safe on the channeling front. If you feel that this preinfusion is squashing the flavours of the individual SOs out of your espresso, this wont be related to channeling and you might be able to fix it by dosing down with a finer grind.

          Cheers,

          Luca

          Comment


          • #6
            Re: Chanelling?

            Luca, I always love your informative and intelligent replies.

            Im not sure if its related to a dud batch of old beans or not. I still see these dents in the top of the puck pretty often. Will try again soon with some fresher beans.

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            • #7
              Re: Chanelling?

              Hey Matt,

              Youre welcome to the advice. Was it helpful? How did you go?

              Cheers,

              Luca

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              • #8
                Re: Chanelling?

                Seems to be better. Ive been using the single filter a lot this week as my wifes been off the coffee (sick), and with a fresher batch of beans (different blend too), theres been less issues.

                The other cause may have been updosing/knocking the top off the puck on the showerscreen upon insertion - is this likely?

                PS Ill hopefully be down at the Viaduct this weekend to see Dave Makin and Carl Sara et al...

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