I consistently get channeling if the group head is below 90C on my LP (what I mean is that I'm getting multiple streams from the naked portafilter). Doing everything identically, but temperature surfing to 90+ prevents this. This seems to contradict expectations: https://www.baristahustle.com/blog/temp ... en-effect/

What is going on? Why would this occur?

The article you linked is very much about temperature, and only mentions prep in passing. Channeling is a prep problem.

How are you preparing your puck? Do you stir the grind (WDT), How do you level the bed? Do you tamp?

WDT is very useful for getting good distribution which by itself could eliminate your channeling problems. Hard tamping is not necessary, but having a level bed is critical from my experience. In fact I have a couple of very nice tampers that never get used anymore. I use a simple leveling tool, with no follow up tamp. I never have channeling.

In addition to the puck prep comments, if you aren't already using one...consider a puck screen. It's cheap potential insurance against channeling if one's puck prep is a bit off. It can't forgive all. But it's one of those situations--"Better to have it and not need it than to need it and not have it".

Grinder? Do you single dose? Do you purge before grinding shot?
I tried a Virtuoso for drip and it was an electrostatic particle separator.

A screen reduces headspace. If distribution is bad, the screen could end up tilted making things a whole lot worse.

IMO, screens are a Band-Aid for other issues. And yes, I tried several.

The vertical space taken up by a puck screen is negligible. If its thickness is a problem, then the dose is absolutely too big. Period.

cafeIKE wrote:Grinder? Do you single dose? Do you purge before grinding shot?
I tried a Virtuoso for drip and it was an electrostatic particle separator.

Grinder indeed. Uneven grounds are a great way to create channeling.