Does pour starting at lower pressure mean it's channeling?

by **satjat** on Sun Sep 19, 2010 4:52 am

I have a weird problem with my Isomac Zaffiro.
When pulling the lever to start the brewing the pressure is at 0 (I pull some water through the wand, if it is not, to equalize).
The pump starts working and when pressure is around 4 bar coffee starts pouring. The weird thing is that pressure keeps rising and stabilizes at 11 bar.

If this indicates some kind of channeling is it normal for the pressure to keep rising?
The coffee coming out at 4 bar is pretty much watery and foam starts to form as the pressure rises.
Putting in the cup after a few drops are out (losing the first few ml) makes a huge difference in the final taste. Channeling shouldn't have that effect according to my limited knowledge.
Another possible cause is that the basket (provided by Isomac as "double") is quite large. I believe the clearance between the puck and the screen might be more than enough.

Any help is deeply appreciated.

by HB on Sun Sep 19, 2010 9:43 am

satjat wrote:The pump starts working and when pressure is around 4 bar coffee starts pouring. The weird thing is that pressure keeps rising and stabilizes at 11 bar.

You should reduce the maximum brew pressure. See Isomac Zaffiro brew pressure too high for more information.

satjat wrote:If this indicates some kind of channeling is it normal for the pressure to keep rising?

This point comes up in I still don't get it: Why adjust the OPV? albeit indirectly. Short answer: For vibratory pumps, the pressure will rise to the maximum of the puck resistance or over-pressure valve setting, whichever is higher. Unless you have massive channeling (as in a 5 second pour), the brew pressure will rise to the OPV setting.

Apart from setting the pump pressure, I don't find the reading of the onboard brew pressure gauge useful. Or, to put it another way, I find it as useful as the "idiot" lights on the dashboard of a car that indicate the engine has stalled. That is, it only confirms what is plainly evident from other sources.

Just to be certain it's covered, I'll repost my recommendation from another thread:

HB wrote:...it sounds like your espresso extractions are channeling. Cause? The grind is off, the coffee is stale, or your distribution/tamp are wonky.

You didn't mention the grinder or the freshness of the coffee, but those are far more important contributors to good espresso than tamp pressure; my rule is simple: Keep it straight and level, keep it consistent. I recommend coffee that is 4-7 days post-roast from a reputable roaster; by post-roast, I mean when it was roasted, not when the bag was opened . From there, review the various how-to guides, e.g., Home Barista's Guide to Espresso and Randy's EASY GUIDE TO BETTER ESPRESSO AT HOME. Jim's Mano Lite: A Short Guide to Dialing in Espresso SOs and Blends offers more advanced diagnosis hints.

The key is improving your technique. If you're short on time and patience, refer to the reliable 1, 2, 3 punch for technique recommendations and the Home Barista's Guide to Espresso for everything else.

More specific to your situation, also see Rocky thread slop and the teflon tape fix and When did this espresso extraction go blond?

by **satjat** on Sun Sep 19, 2010 12:08 pm

Thanks for the extensive reply.
It looks like my problem is with channeling after all.

I can see that the side of the puck is mostly leaking (I don't have a naked pf so it is my judgement by checking the puck). Does this indicate a bad quality basket?
Does basket size have anything to do with this?
Similar to a double basket not being good for single doses and will cause major channeling (or "soup-ing"), this basket is more like a triple (if such a thing exists). I will try with a smaller and better quality basket to solve both problems at once (hopefully) or start dosing for triple since that produces better results (but requires too much coffee, and produces too much coffee too).

by HB on Sun Sep 19, 2010 12:23 pm

No, I don't believe this is a basket issue, though you may find it easier to properly prepare the puck with a (shallower) double basket. I am nearly certain the problem is on the handle side of the portafilter because although some espresso machines are fussy about excessive head clearance, the E61 is not. In my experience, E61 espresso machines are more forgiving with a bit of extra clearance, not less, assuming of course the distribution is correct, the coffee is fresh, and you're using a good grinder.

I recommend you get a bottomless portafilter or modify your existing one. There's plenty of threads describing how to modify yours and that will give us some meaningful information. At this point I'm speculating and that can only help you so far.

PS: As for the appearance of the puck... see Puckology Challenge for a discussion of its usefulness (in my opinion, as long as the pucks are consistent in firmness/wetness, you've extracted all the useful information from puck assessment).


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