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Help with channeling

Postby williamsavona on Sat Mar 09, 2013 1:58 pm

Having a very hard time getting rid of channeling around the edge of the filter basket. Here are some pictures of one of the worst instances I've had recently.

Image
Image

Things I've tried from reading everything I can find on subject here:

1. I've been making sure the basket is very dry and pre heated.

2. I've tried several distribution techniques (WDT made things worse, NSEW seems to help most)

3. I've made sure that the puck is not being disturbed by the screen.

Maybe I am missing something obvious, I am new at this. :?
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Postby heavyduty on Sat Mar 09, 2013 2:51 pm

Are you using some kind of dosing funnel? When you do your NSEW, try gently pushing the grounds from the center on out.
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Postby bostonbuzz on Sat Mar 09, 2013 3:21 pm

Try dosing a bit less.

One suspicion is that when a basket is overdosed, the dispersion/shower screen presses on the expanded puck, while the outsides are free to expand and therefore are less dense and it leads to channeling. Different machines require more headspace above the top of the tamped puck.

The standard test is to dose and tamp normally and put a nickel on top of the puck. Lock and unlock the portafilter and adjust the dose so that the nickel is only the tiniest bit pressed into the puck. This is roughly the max dose.

Alternatively, just dose 2 grams less and see if this helps (adjusting grind accordingly).
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Postby RapidCoffee on Sat Mar 09, 2013 3:44 pm

Highly recommended accessories:
* 0.1g scale
* bottomless portafilter

How did you decide that you have a problem with edge channeling? Have you observed it with a bottomless portafilter? (Sorry, can't tell from your pix.) If not... well, puckology is an arcane science. I don't find much value in it. Get a bottomless portafilter, then you will know whether you really have edge channeling.

Even more important: get a 0.1g resolution scale, and start weighing your doses. If you are dosing over 16g in the double basket, then I concur with the downdosing suggestion.

There is no reason why the WDT, done properly, should cause channeling. If you are using a blunt stirring tool (like a chopstick), then try something thinner (like a dissecting needle). If your dosing funnel extends deeply into the basket, trim the bottom of the funnel until it only extends 1/8" into the basket. After removing the funnel, you can give the grinds a little shake to eliminate any possibility of leaving a gap at the edge.

You may wish to try nutation before tamping. Nutation can improve grinds distribution and help with edge sealing.
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Postby JmanEspresso on Sat Mar 09, 2013 4:30 pm

If thats the only evidence you are basing your theory of edge channeling on, its means little to nothing.

Check with a bottomless portafilter. Its the only real way to know. Those little holes could simply be caused by the 9bars of water pressure that was sucked off the top of the puck at warp speed by the 3way valve at the end of the shot...
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Postby pizzaman383 on Sat Mar 09, 2013 8:27 pm

I had sprites and edge channeling with the EPNW ridged basket. Switching to the ridge less has eliminated them. With the ridge less there is no taper so there is more coffee on the edges and I get fewer sprites and edge channeling.
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Postby heavyduty on Sat Mar 09, 2013 9:10 pm

^^^ I was thinking about this also after posting earlier; not being familiar with the basket being used, whether the tamper was the right size for the basket and that they were working together in unison (so to speak). Nutation is a good idea as RapidCoffee mentioned, short of a new basket or convex tamper.
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Postby allon on Sat Mar 09, 2013 9:29 pm

tapping after tamping can break the adhesion with the walls.
What's your basket prep like?
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Postby williamsavona on Sat Mar 09, 2013 11:26 pm

Thanks so much for your help guys!

Sorry for leaving out some important details. I am using a bottomless portafilter with a triple basket and about 19-20 grams of coffee (I have a horrible 1g scale, which will soon be replaced by the .1g scale suggested). It's a 58mm basket and I am using a 58mm flat tamper to tamp. I do a light tamp down and then gently use the tamper to press against the NSEW walls of the basket, then straight down final tamp, no rotation of the tamper, just straight out.

Just pulled a couple shots to attempt some video for you guys. I apologize for the shaky quality, I've had too much espresso. :)

Video 1: WDT using a very thin bambo skewer (a dissecting needle seems to create clumps) for a few seconds, very gentle shake and then tamping routine described above.


Video 2: NSEW
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Postby RapidCoffee on Sun Mar 10, 2013 12:23 am

Thanks for posting the videos, that helps a lot. There's good news and bad news. The good news: no obvious edge channeling. The bad news: plenty of other flaws to worry about.

The first pour extracts unevenly, starting from the rear, and has a bad spritzer. The second pour is a bit of a gusher, and extracts very unevenly (also starting from the rear). This means you are front loading the basket. Make sure the grinds are distributed as evenly as possible before you tamp.

When you tamp, your primary goal should be, not to screw up the distribution. So consider eliminating the NSEW Staub tamp until the uneven extraction issues get resolved. Otherwise your technique sounds OK. (Side note: I can't imagine why stirring with a dissecting needle would cause clumps, but not a bamboo skewer.)

Forgive the obvious questions, but are you using freshly roasted artisanal coffee? Are the burrs on your Mazzer Mini broken in (or in need of replacement)? Have you checked the pump pressure on your Rocket? High brew pressures (over 9 bar) can exacerbate extraction issues.

Suggestion: try using the double basket, at least until you nail your technique. Triples are more tricky IMHO, and 19g in a triple is pretty serious downdosing (many dose 19g in a double). Start with a dose of ~16g in your standard double basket, then adjust the dose up or down as needed.
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