Longer pre-infusion for less channeling? - Page 3

Beginner and pro baristas share tips and tricks for making espresso.
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lassepavoni (original poster)
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#21: Post by lassepavoni (original poster) »

baldheadracing wrote:Do you have temp strips or a grouphead temp sensor on your machine?
I do have a capillary thermometer attached to the group head, but it is pretty useless actually. It takes a couple of minutes to get up to temp, so to speak, then maxes out at 91°C and doesn't budge as long as the machine is hot. It does that every time, so it is pretty repeatable :roll: . I had a digital thermometer hooked up for a couple of pulls, an that one responded to every half pump. The analog one is just crap, but doesn't use batteries.

baldheadracing wrote:I would say that you are grinding way too fine, and as a result pulling down with too much force - I suspect anyone would get channeling in such a situation.

I would also suggest dropping the dose to 14g, or maybe even 12g.
So I did another test run this morning. Wanted to follow your suggestions, so I decided to change two variables at once, namely the dose and the grind setting. Basically the same procedure as in the previous run, but now using only 14g instead of 16g and starting out with a much coarser grind.
Shot	PI	Pull	Grind
1	4s	8s	+2 coarser
2	12s	13s	+1 coarser
3	38s	18s	+2/3 coarser
4	none	16s	+1/3 coarser
5	none	33s	normal
For the first shot I started out two full clicks coarser. After pulling up the lever I've had just enough time to quickly put the cup under the spout to catch the first drop, and the pull just rushed through without any noticeable resistance on the lever.
The second shot, a whole click finer, wasn't much better. Pull time much too short, barely any resistance on the lever.
Third shot, another 1/3 click finer, got closer to the ballpark but still was much too runny. All sink shots up to now.
Fourth shot, now just 1/3 click coarser than my usual setting, I skipped the PI and immediately started the pull, deliberately applying less pressure on the lever. Still a little short on pull time, might just as well been due to especially bad puck prep for this one.
Fifth shot, back to normal grind setting, still on 14g, no PI, normal pressure applied to the lever, yielded a good pull time and a drinkable shot.

Thoughts?
I don't think that I am grinding way too fine, because the pull times for the coarser settings are much too short. The result in the cup is runny, with the little bit of crema disappearing within the next 20 seconds, leaving a sour slug in the cup. Maybe those shots would be acceptable to somebody else, but I for one certainly don't like them.
This experiment shows nicely how I ended up at my current settings. I can't grind much coarser because that yields runny shots, and I can't grind much finer, because then the grinding takes like forever and the machine chokes. In my opinion that leaves me with the possibility of an insufficient grinder, i.e. the sweet spot is somewhere in-between the clicks and I can't reach that, or that my puck prep is subpar and produces too much channeling. That second one is what Chris PIXIllate suggests, and something that I might overcome with better tools and more practicing. Time will tell, hopefully, but I've had enough caffeine for this week now.
Regards, Lasse
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PIXIllate
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#22: Post by PIXIllate »

Try different coffee. What are you using and how old is it?

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lassepavoni (original poster)
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#23: Post by lassepavoni (original poster) »

Today I used an ecuadorian 100% robusta from Giomar Hidalgo, 8 weeks post roast, and yesterday a 100% robusta from Mamy Dioubaté of Guinea, 7 weeks post roast. Admittedly both a little old by now, but I don't have any more fresh roast ready at the moment. Will fire up the roaster in the coming days, as soon as time and weather permit, and then have some fresh beans ready for further testing.
Is it possible that the main reason for my problem here are stale beans, and that it is nigh impossible to get a good extraction out of them with an Europiccola?
Regards, Lasse
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#24: Post by PIXIllate »

2 month old, home roasted 100% Robusta. Sorry, I don't have enough experience to tell what an ideal extraction or taste profile should be.

If you want to work on your puck prep my advice would be to get a freah roast from a well known roaster or at least buy a bag of Lavazza Super Crema and start from there.

Not many people here drinking 100% Robusta.

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lassepavoni (original poster)
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#25: Post by lassepavoni (original poster) »

Those two were not home roasted, sorry if I wasn't clear about that. They were both from kaffemacher.ch, 250g bag each. Since I don't drink a lot of coffee and like to tinker with electronics, I started out with a modified popcorn machine and figured that it might be a good idea to roast a 100g batch every other week instead of buying a single 250g or 500g bag and have it sit for a couple of months. When I ordered fresh greens a couple of weeks back, I also ordered those two bags of roasted beans, since they were 100% robusta and seemed interesting to me. Due to "plenty" stock of roasted beans, I didn't roast my own for some time; but now that I need to replenish, the next batch will be home roasted.
Regards, Lasse
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baldheadracing
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#26: Post by baldheadracing »

lassepavoni wrote:Thoughts?
The first thing is to only change one thing at a time.

The second thing is, at this point, I would suggest always pulling two shots without changing coffee, grind size, dose, etc. If you don't get close-to-identical results between the two shots, then that variability has to be addressed first. On a Pavoni, that means that you are going to have to manage temperature. Use your digital thermometer.

Here's an example:

This isn't going to be exactly like your machine; the graph is only to give you an idea of the curve of readings that you might see from a grouphead thermometer. The red line is my grouphead thermometer probe - exact temps will vary depending on location, etc. - the green line is a second probe that is resting on top of the puck. I'm aiming for an average extraction temperature of 90C because this is a 50:50 Arabica:Robusta blend roasted Neapolitan dark ( Saka Crema Bar - https://sakacaffe.it/prodotti/bar-line/ ... offee-1kg/ ).

For the second shot I would shut the machine off and wait until the grouphead thermometer was reading well below 55C. (There are many other ways, but that is a whole different discussion.)

0:00 Machine turned on (not shown). The starting grouphead temperature 18.3C (winter in that room that isn't directly heated)
~7:30 Grouphead temp reaches 55C, I do three slow half-pumps of the lever (no water exits group). The group heats up.
~8:00 Portafilter locked in when the grouphead temperature reaches 80C; raise lever, etc.
~8:30 Water starts to rush into the group; pre-infusion starts
~8:40 I start pulling down on the lever (10 second pre-infusion)
~9:15 I let go of the lever and pull the cup away (35 seconds of extraction, 14g dose:29.7g out).


Other details:
-I'm using a modified first-gen Europiccola, a.k.a., 'Ultimate Europiccola.' Pressurestat is set at 1.05 bar for better steaming, but the higher setting means more active management of brew temperature is needed;
-14g dose in a Streitman '17g' basket (very similar to current stock Pavoni double baskets)
-Orphan Espresso Fixie hand grinder; "3b0s0f" is the grind setting
-Boiler level 4cm from bottom of the visible part of the sight glass (makes a difference for warm-up time, and maybe a very slight difference in grouphead heating)
-"Good quality brings happiness as you use it" - Nobuho Miya, Kamasada

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lassepavoni (original poster)
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#27: Post by lassepavoni (original poster) »

baldheadracing wrote:The first thing is to only change one thing at a time.
Sure thing. Since I usually don't pull more than two or three shots a week, sometimes none at all, it's pretty tough to be precise and scientific.

baldheadracing wrote:On a Pavoni, that means that you are going to have to manage temperature. Use your digital thermometer.
Temperature is still a big :?: in terms of variability. I don't try to hit an exact temperature each time, but instead just aim for ''hot enough''. In fact, if I only do three half pumps before the first shot, the result in the cup is actually rather cold. And those cold shots have never been to my liking. On the other hand, I have just lately managed to achieve two almost excellent shots in a row, with my usual routine and thoroughly pre-heated machine. I have not been able to relate good or bad shots to the temperature of the machine in any other way, except for ''too cold''.
From what I've read so far, 1) the post-millennium group is not as prone to temperature runaway as the pre-mill group, and 2) the hotter the brew temp, the more bitter and less sour the result tends to be. Never read anything about the influence of brew temp on channeling or extraction time though. That's why I have left the temperature juggling ball on the floor for now, so to speak, and didn't consider it as a possible culprit.
Regards, Lasse
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lassepavoni (original poster)
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#28: Post by lassepavoni (original poster) »

Received my new toys today and just had to give them a first try. Pulled two shots with the bottomless portafilter (but the same basket as before) and used the new WDT tool and the fresh beans that I roasted just yesterday. They are a little far on the dark side, so I mixed them with some older medium roast for the second shot. Both pulls looked pretty good to me, with no spritzers or premature blonding. The second one took almost a minute, because I did not adjust to grind a little coarser for the fresh beans. The first one oddly felt pretty spongy, both at the beginning and at the end of the pull; might have been due to the grounds being too fine, too. If you're interested, I can try to share the videos.

I still have some of the beans left that I used last weekend, so I will try to repeat the experiment this weekend, keeping everything the same except for the new WDT tool. Then there's the puck screen and the thermometer/temperature to play with, so lots of things to try for the next weekends.
Regards, Lasse
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lassepavoni (original poster)
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#29: Post by lassepavoni (original poster) »

Oh well, looks like I pretty much messed up the test run for today :oops: .
The only meaningful data might be that of the thermometer. I taped a K-Type thermocouple directly to the group head with some aluminium tape and watched the reading on the multimeter. Temperature idles around 100°C prior to pulling a shot, rises up to around 106°C during the shot, and then slowly goes down back to around 100°C until I am ready to pull the next shot. That was just observing my usual routine, and not trying to do anything different or achieve a certain reading.
Regards, Lasse
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jedovaty
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#30: Post by jedovaty »

Are you spraying with or adding any drops of water before grinding beans to reduce static? If so, try without. I recently noticed a correlation between RDT and channeling issues, did some testing.

After removing RDT from my routine, all problems gone. :D

If you are not, then, I wonder whether you really are experiencing channeling. That's all.