1. How important a factor is the space between the dispersion screen and tamped coffee in the extraction process?
2. Should it be an element that you try to keep consistent?

Pulling shots on the MicroCasa a Leva and using the "Newd" portafilter at a set clearance of ~8mm I've been having problems with a lighter tamp (~#15) vs. ~#30 tamp. The #30 tamp has yielded nice looking extractions and acceptable taste. The #15 have resulted in uneven extraction and unacceptable taste. Shots are pulled the same way.

narc wrote:1. How important a factor is the space between the dispersion screen and tamped coffee in the extraction process?
2. Should it be an element that you try to keep consistent?

Pulling shots on the MicroCasa a Leva and using the "Newd" portafilter at a set clearance of ~8mm I've been having problems with a lighter tamp (~#15) vs. ~#30 tamp. The #30 tamp has yielded nice looking extractions and acceptable taste. The #15 have resulted in uneven extraction and unacceptable taste. Shots are pulled the same way.

Try a < 1# tamp if you really want to say you've tried a "light" tamp. There is very little difference, in my experience (and according to Illy), between 10# and 30#.

Without sufficient headroom the screen tamps the coffee, which is perhaps what you might not want, if you're going for no tamp. If that's your goal, do not overdose, and tamp just lightly enough so the top of the puck clears the screen. Or simply settle the grounds with some chop-chop-chops of the edge of the spoon handle or some light whacks of the PF on the countertop, without a tamp.

On some pump machines, headspace might also affect flow of water into the basket , but you'd have to ask a pump user about that.

Regards
Timo

P.S. Also, you will have to adjust the dose and grind and distribution if you're approaching the 0# tamp. The lack of a tamp is not the cause of uneven extractions when using a spring lever if the basket is dosed moderately, the contents are well distributed and settled, and the fineness of grind is appropriate.

I dose and tamp so that the top of my dry coffee is 5-6mm below the top lip of the basket. This allows a fraction of that space between the coffee and the screen.

Of course, I don't want the coffee to bump the screen. If it does not swell into the screen the screen stays cleaner.

The taper on the single basket (Lusso) pretty well dictates that your headspace be consistent. I think that too much headspace encourages a slurry effect on the top of the puck..

I don't know your machine, but 8mm clearance between puck and screen sounds like more than necessary to me.