Hi Everyone,

I've been a big fan of the board for quite some time;as they say, long time lurker, first time poster...

Anyways, I've been having a problem lately with what appears to be some center channeling when pulling doubles on my Gaggia Coffee. The machine has been calibrated for ~199F deg. brew temp, and is operating at ~11 bar static/~8.5 bar dynamic (modified with adjustable Classic OPV).

I'm using a Mazzer Mini E 'B,' and going through my usual prep routine (grind/dose directly into basket/WDT/ ~30lb tamp), using a weighed 16g dose in naked pf. Upon starting the pump, it looks like I'm getting a good dwell time, and the beading starts out evenly. Then, as the cone starts to form, it flows as normal, but gets bigger rather quickly (coincidentally, there seems to be some early blonding too). I'm hesitant to call it a "gusher," since 25-27 seconds gets me ~1.75oz in the cup. Crema is decent color, but seems thin and is dissipating quicker than normal. Mouth feel is also a bit thin. Plus, I'm getting some small white spots cluing me in to over-extraction, though the taste is only bitter at the top third of the extraction...afterwards it's quite pleasant.

When I remove the pf, it looks as if there's a small imperfection about the size of a nickel right in the center of the puck, with 3-4 pinholes around it. The cake is also visibly lower here. Puck is pretty dry, with the exception of the sides (which seem rather damp), and comes out in one piece when I knock it out.

I've tried downdosing/grinding finer, to no avail. I don't tap when dosing, and am especially careful when handling the tamped pf. I'm reluctant to updose, for fear of impacting the shower screen. Beans are Metropolis Redline, 8 days post-roast. I used to pull great-tasting/looking shots using the same technique. What gives? Any ideas?

Thanks in advance for any suggestions!

-Mike

All coffees don't work at the same measured dose.
Either updose to 16.5 or 17 or grind finer @ 15 or 15.5 or ???

Not that I'm a fan, but you could try Nutation: how to do it right

Thanks for the suggestions!

I tried updosing to 17 grams this morning, ground a little coarser, with a small nutating tamp; the cone wasn't as large but the shot was considerably more bitter than either the 15g or 16g dose from yesterday. After removing the pf I'm still seeing the little "turbulence mark" which is a little off center (where I used to see a flat surface with a slight screen imprint and screw mark), and still about the size of a nickel. The rest of the surface seems alright--maybe a tiny bit soggy if anything but doesn't look too terribly disturbed.

I knocked the puck out carefully to have a look, and it still seems quite soggy around the edges, with a dry, compacted center (when looking at the bottom). There seems to be some prevalent channeling going on here, and I'm still not quite sure why

FWIW, I'm able to brew an awesome-tasting single, using the single basket with an 11.5g dose. I still think I'm getting some channeling even with this shot, but I'll attribute that more to the funky shape of the Gaggia single basket.

-Mike

The goal is that all parts of the puck receive equal saturation, yes? We just starting using our new machine today and that's what seems to be happening. No part of the puck is dry, no part is soggy, it seems to be uniformly wet throughout.

Is that the goal?

Yes, that is the goal....

At least I would think? I tried a 14g dose this morning, and although it tasted much better (most of the bitters were gone), I was still seeing a bit of channeling and resultant early blonding. Perhaps I have to fiddle with the grind a little more?

I did the nickel test, and when I lock in then remove the pf there's no imprint at all on the puck. If I updose to remedy that, I start tasting bitterness.

Is there any chance the problem could point to dull burrs on my Mini E?

-Mike

Is there any chance the problem could point to dull burrs on my Mini E?

What you described -- enlarged cone and early blonding -- describes what I experienced on my Macap. I estimated 500 lbs through the old burrs and had expected more miles before a change. I reluctantly changed out burrs and voila, all problems ended. Enlarged cone gone, early blonding gone.

Life is good.

B|Java

I have a new set of burrs; I think I'll install them this weekend.

I bought my Mini E used (it's a 2006 model), and although I thought the burrs looked OK when I did the initial cleaning/disassembling when I first took it home, I could be wrong.

I also have the sneaking suspicion that the channeling could be related to pop-corning. I single-dose (using a scale, so at least I can rule out any inconsistency in that area), but I usually just close the little sliding tab at the bottom of the hopper before I turn on the motor. Could this be contributing to the problem?

I'm determined to get to the bottom of this....I remember reading that these Gaggia semi-autos are designed for the Italian standard of 14g of coffee, and that they do not play well with higher doses. I know for sure that I get more bitterness when I use the overfill/WDT/tamp method (which I'm guessing has something to do with the puck impacting the shower screen). Nevertheless, I believe I should be able to pull a 14g shot with no channeling.

-Mike

Well I changed the burrs over the weekend, unfortunately to no avail

I guess on the good side of things tho, I now have a perfectly-good set of spare burrs. But I digress....

Then, before I pulled a second shot, I decided to lower the brew pressure on my machine to see if it would have any impact--it did not, aside from some taste differences.

I'm going to have to go back to the basics on distribution and make some changes. BTW, when I knock the puck out after I've pulled my shot, some of the sides remain stuck to the basket wall (similar to the way they do when pulling singles with the single basket). Does this point to side channeling? If so, how might I come up with a fix?

Thanks!

-Mike

Here's a few pics I took after a channel-plagued pull using a 16g dose:




Some coffee always seems to stick like this when I knock the puck out




-Mike

Is the center indentation from the shower screen?