Where to start?

[kaffelogic]

At the moment we have a small selection of profiles available here. We are working to expand the available profiles and advice about which to use. Also users and green bean retailers will start to post their recommendations in the future.

[Angela]

Hmmm, after a few weeks of great espresso roasted at 3.6 that grinds nearly exactly like commercially roasted beans do I decided to splash out and buy 3kg of Guatemala (albeit a different variety than I have been using).

I tried my first roast of the new batch today and it's acting like the Colombian beans I initially posted here about, needing to be ground very fine (2 settings finer than I've ever needed to grind), and even then it's still losing pressure mid extraction and dropping out too fast towards the end of the shot.

Has anyone else found that some bean varieties need top be ground unusually fine?? I'm wondering if I need to compensate by adjusting the roast profile. I only use the default one.

I've noticed exactly the same about grind size. I think those beans subject to static charge need a finer grind. I use a Niche Zero grinder (also crowd funded at the start) and it has a collection cup for the grinds which one inverts into the portafilter. Static, finer grind beans leave a cup-edge-sculpted high mountain of coffee whereas less clinging coffee can be ground courser.

Losing pressure mid-way can be a sign of channelling; did you see any evidence in the puck? Are you tamping well? Some people stir the grinds in the portafilter before tamping to more evenly distribute the fines and claim it makes a difference. I'm not at that level anality yet but probably will be soon.

[Noob]

Have you tried this for static? https://www.youtube.com/watch?v=T0Dh1W40ILY

I'm not convinced this problem is static or channelling though. My suspicion is that it's something to do with the roasting of certain beans. It's all I can come back to as it has only happened to 3 varieties of beans. The other varieties I've tried are fine, pressure comes up and stays up for the duration of a good shot and flows well for at least 30 sec.

I've got an Anfim Best grinder and weigh my grinds in the basket, use a distribution tool (and have tried other distribution methods) and a calibrated tamp (and my standard tamp), I'm 99.99% sure it's not channelling. I've even tried adjusting pre-infusion time on my espresso machine just in case that made a difference (it didn't help). The net result is always a super fine grind, pressure comes up but once extraction starts the flow rate increases quickly resulting in pressure dropping off before a good shot is pulled (exactly like you would expect from channelling).

I've downloaded the Firestarter and Ninja roasts and roasted both those last night. It'll be interesting to see if (once I get them dialed in) the flow rate acts normally. I'll be trying that Tuesday or Wednesday next week so will report back

[Angela]

I tend to breathe into the cup of grounds before upending into the portafilter if I know there is the likelihood of static. Same answer - add moisture - different approach. I've seen some people use a mist spray. I value my grinder burs too much to add moisture into the grind chamber.

Channelling is obvious if you have it. I use an open portafilter that allows much closer scrutiny of what's going on; I can recommend that.

[kaffelogic]

I'm not convinced this problem is static or channelling though. My suspicion is that it's something to do with the roasting of certain beans. It's all I can come back to as it has only happened to 3 varieties of beans. The other varieties I've tried are fine, pressure comes up and stays up for the duration of a good shot and flows well for at least 30 sec.

I think, given what you are describing here, that you have eliminated static as being the issue. Static is very noticeable, and can be irritating, but doesn't explain what you are seeing.

I've downloaded the Firestarter and Ninja roasts and roasted both those last night.

Both the default and Ninja start fast. Firestarter and Filter start slow. So low density beans will maybe be better suited to Firestarter and Filter. I am very interested to hear your findings.