I have a Linea Mini espresso machine, using the VST 20g basket, and have the Niche Zero and Lagom P100 grinders. When I try and pull a shot of light roast beans (Maria Jose Tinoco Espresso) using the P100 I can never get it to pull anywhere close to a constant flow rate. With the Niche at grind setting 22 (for this particular coffee) I get a good shot - starts out slow, ramps up to about 1.5g/s and very slowly pulls faster until I get my 40g out for my 19g in after 32 seconds. With the P100 if I grind coarser, it just flows out in 10 - 15 seconds. If I grind finer, the initial time to first drip is slower (perhaps 10 seconds), then it ramps up quickly from 0g/s to 4g/s and ends up being underextracted (less sweet, bit more acidic) as it just gushes out way too quickly - probably channeling.

I do the same for puck prep between both grinders - WDT of the grinds, tap the portafilter to even out the grinds, then tamp straight and with similar pressure. The Niche always have a more linear flow rate than the P100. See below graph for the P100. Grinding finer will not help as even on 0.8 it now takes 10-15 seconds to start extracting then it just gushes out in the last 15 seconds. I can see it starts out evenly when looking at the bottom of the (bottomless) portafilter. What can I do? I thought the whole point of large flat burrs is to improve the clarity of light roasts, yet I cannot get a good extraction.

May you have to modify the weight inside the basket. Is not the same flat burrs and conical burrs.

Is this the sort of thing that pre-infusion is supposed to help with?

Jake_G wrote:Turn your brew pressure down to 6 bar.

This might help but switching it between 6 and 9 bar every time I switch grinders (I like to explore the differences between them for different roasts) will be annoying...

skink91 wrote:Is this the sort of thing that pre-infusion is supposed to help with?

No. You want less preinfusion for these high clarity flats and their more unimodal grind size.

To the OP: You'll likely have better luck with turbo-style shots. Those HU burrs are high extraction burrs and you don't need to approach espresso with the traditional 9bar/30sec mindset.

EvanOz85 wrote:You'll likely have better luck with turbo-style shots. Those HU burrs are high extraction burrs and you don't need to approach espresso with the traditional 9bar/30sec mindset.

I will certainly give that a try. Any other suggestions for trying and improving the shot flow rate apart from dose size for the more traditional style shots? Puck screens? Filter paper in bottom of portafilter? How do you guys get good traditional shots with the P100 and lighter roasts?

Thanks - I will play around some more with dose size etc. and compare the taste with my Niche to see if I can concentrate more on actual taste than some numerical goal.

As an aside - would a 0.6mm gicleur make a difference? Or is it recommended to first drop pressure to 6bar should I go that route?

I have a GS/3 with the .6mm gicleur and immediately noticed what you are seeing with light roasts. This was even apparent with my 64mm HU burrs in the Super Jolly. Flow control was a must for me, but I've since tried adapting to lower pressure shots instead of flow control and the results are very good. I've been at 6 bar since May of this year and have not really missed having flow control.

I will reinstall it in the coming months and see if a flame is rekindled, but for now, I'm perfectly happy without it - hence my initial one-liner response

Cheers!

- Jake