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Thread: Coffee mostly extracting around the edges of the basket

  1. #1
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    Question Coffee mostly extracting around the edges of the basket

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Hi All,


    I always use a naked (bottomless) portafilter to extract coffee
    and notice that coffee starts to extract around to the edges of the basket, not in the middle.


    I've got an impression that it almost does not pour through the centre of the coffee cake.


    I'm blaming the tamper which is a bit loose in the basket and does not fit tightly, which leaves narrow untamped area around the edges of the basket.


    I'm really concerned that my entire shot is pulled from the small amount of coffee around the edges and not the whole coffee cake


    How to resolve?


    It must be unnoticed on portafilters with the bottom.
    Those who use naked portafilters, do you notice the same problem or your tampers fit tightly into the basket?


    Thank you

  2. #2
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    Which machine, and does the middle fill in pretty quickly?

    The oft seen practice of tapping the tamped portafilter with the tamper can lead to perimeter channel. Also be light when locking the portafilter into the group head, it doesn't take much to lose that seal around the edge.

    You can also try moving the tamper to north edge of the basket and tamping, then east, tamp, south and west. If your basket is tapered, you can try dosing less or tamping harder until the tamper does get stopped by the outer walls.

  3. #3
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    Re: Coffee mostly extracting around the edges of the basket

    I get this with my bes820. Im using a krups basket which is tapered at the bottom to a perforated section about half the diameter of the top of the basket. It can take half of the pour to show in the middle - on a really tight pour it sometimes doesnt get there.

    I've been under the assumption its because I tamp when the gounds are forming a natural heap (I.e. more in the centre), so the puck is firmer in the centre. That said, I havent managed to alleviate the problem by inverting this (I.e. making a depression in the centre prior to tamping.

    I dont think it is channeling at the walls for me, as the coffee is very dark and viscous.

  4. #4
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    It's it a single or double basket? Could be the tapered edges causing it. Alternatively try a finer grind and lighter tamp, or use a slightly nutating motion when tamping (does the same as the NESW tamp).

  5. #5
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    I too do a nutating tamp by swivelling the tamper handle with a circular motion before I polish the puck. I think that this distributes and mixes the coffee, breaking up clumps and channels resulting in a more even extraction.

    I use the naked portafilter most of the time with the single filter.

    Barry
    Last edited by Barry_Duncan; 23rd April 2013 at 10:41 AM.

  6. #6
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    Re: Coffee mostly extracting around the edges of the basket

    Quote Originally Posted by Gnat View Post
    It's it a single or double basket? Could be the tapered edges causing it. Alternatively try a finer grind and lighter tamp, or use a slightly nutating motion when tamping (does the same as the NESW tamp).
    If this is for me:
    Its a double. The taper is quite sharp - roughly 45 from about halfway down the basket. Ill keep working on the balance of fineness (hard on am em480) and tamp pressure. From experience so far it doesnt seem to prevent the pour starting from the outside, just gets to the 'whole basket' pour quicker.

    Ive just had a thought - I wonder if it could be related to the group/show screen design? Tends to flow from four points about halfway out from the centre of the shower screen.

  7. #7
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    Quote Originally Posted by MrJack View Post
    If this is for me:
    Its a double. The taper is quite sharp - roughly 45 from about halfway down the basket. Ill keep working on the balance of fineness (hard on am em480) and tamp pressure. From experience so far it doesnt seem to prevent the pour starting from the outside, just gets to the 'whole basket' pour quicker.
    I just got my naked portafilter yesterday (first use this morning), here is my experience so far. The pour does start from the outer edges of the basket, then will move quickly into the centre (within 0.5-1 second). No channeling, and it will quickly merge into the single stream from the centre.

    Quote Originally Posted by MrJack View Post
    Ive just had a thought - I wonder if it could be related to the group/show screen design? Tends to flow from four points about halfway out from the centre of the shower screen.
    This is due to the dispersion block (sits right above the showerscreen). Its basically a rubber/plastic/metal block with holes machined out of it, designed to disperse the flow from the pump evenly around the showerscreen. Different machines have different numbers of holes (mine has 8, but its a 58mm basket), so this should not be an issue.

    If the shot tastes good, I wouldn't stress over it too much.

    Here is my nutating tamp (make small circular motions as you press down on the grinds). If you keep watching you'll see the pour start at the outside edge and move into the centre

  8. #8
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    Siberian,

    As you have already identified, the discrepancy between the diameter of the tamper and the diameter of the basket may be contributing to the problem (maybe try sourcing an appropriately sized tamper, if you can afford it).

    I've experienced what you've mentioned before.

    Try lowering your dosage, and making the grind finer. Sometimes using a high dose with inadequate distribution will manifest itself in a form of channeling within the extraction (like what you've said).

    Also, I'd pay close attention to how you're distributing the coffee... try and make sure it's as even as possible, and distributed around the edges too.

    Hope this helps in some way

    Best of luck

  9. #9
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    I agree that distribution issues can cause a donut extraction. I do three things which have reduced the tendency for this type of extraction to occur:
    1. I stir my grounds with a bamboo skewer. On Home-Barista they refer to this as WDT or the Weiss Distribution Technique;
    2. I then groom the basket using Scotty Calahan dosing tools; and
    3. I also use a convex base tamper.

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    With my Perfetta (which is very dose/tamp sensitive) I find that either underdose or overdose produces an uneven pour that will be noticeable in the different pour rates from each of the spouts on the double portafilter.
    I interpret this as channeling and I agree that a contributing element is probably a very fine ring of 'underpacked' grounds around the perimeter of the basket, which can be eliminated with a slight adjustment to the tamp technique.



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