Some coffees Brett are pre-disposed to exacerbating channeling. It's been a long journey for me over 40 years, but I can now put that "phenomenon" aside and know how to deal with it. The extraction method (lever versus pump) won't make it much worse, I've found that some coffees, regardless of the roast profile, will promote a degree of channeling. It's got to do with a concept called abnormal Water Activity and it's impact upon both the roasting process and the espresso extraction. The cell structure of the coffee is not right.....and hence when it's ground the particles are literally "all over the place". In the last few years I've had some green coffees with abnormal water activity (these have been returned to sender). I had no measurement method at the time (still don't, but I know the key signs of abnormal water activity as it roasts outside of the standard params). Water activity in relation to green coffee is a science more advanced than moisture and density traditionally used by all parties in the raw coffee supply chain. In the roaster, abnormal water activity (depending upon which end of the spectrum it's at) would either roast with no heat, or excessive heat (normally it's a combination of unripes + abnormal water activity). In the grinder, the roasted coffee has a tendency to choke or gush with very little tolerance in between (and a lot of frustration by the operator). In the cup, it's bland, boring and lacking just about everything - no flavour, no acids, no body, no wow !. Abnormal water activity can be common in green (raw) coffees. It's caused by improper drying of the greens during processing. Thing is, you can look at the coffee, smell the coffee, test it's moisture and density and with all the green ticks, proceed to roast it and "wowza.....something's not right". Most of the bigger green brokers are scrambling to get water activity measurements on coffee. Why ? because the green coffee when it's abnormal must be used or roasted ASAP. The longer it's sitting around in a warehouse, the more problematic it becomes. So, getting back to your channeling issue - it can be from the roast and/or it can be from the greens. Yes, technique plays a role in the process and the likes of dosing tools can help "compensate" for problems and in the absence of roast "data" I'd say the coffee might have something that's promoting channeling like abnormal water activity. In reality, the likelihood of a roast profile defect is higher than a defect of the raw coffee. Some coffees are difficult to work with......we know that already..........Brazil and Ethiopian naturals, some high grade Kenyans and washed Ethiopians, Sumatrans, Monsooned coffees - all present challenges in espresso extraction if the roast has not been absolutely nailed. A good barista or operator can identify when there is something wrong - extractions that are choking too easily, the need to adjust the grinder way out of the norm, etc. all these point to roasts or water activity that's not ideal. When there is a Water Activity issue, no amount of supa-dupa roasting skill is going to polish it into something that's acceptable or normal - trust me, I've tried and tried 1,000's of times over. Happy Easter.
