A while back I ordered a 51mm puck screen, that fits the semi-flat bottom of my 54mm basket (I imagine 53.5mm screens would work similar for 58mm baskets). My idea was to allow more paths for the water to exit the bottom of the puck, allowing a more even extraction and finer grind.

I just got it and have only pulled a few shots. I needed a substantially finer grind: My major espresso range is 2.9-3.0 for light roast and 3.0-3.1 for medium roasts - adding the bottom filter moved my current coffee (Colombian pink bourbon and geisha from Jaime, roasted by The Coffee Collective) from 2.9 to 2.8 (i.e. decaf range).

In the cup, I noted a more intensive flavour profile with both increased body and clarity. I've previously experimented with bottom paper filters but here the effect on flavour has been less pronounced and I haven't liked the thin body it produced.

The screen has been deformed by the extraction pressure to conform to the basket but has, however, slightly scratched my filter basket. Additionally, and makes it impossible to diagnose puck prep by looking at the bottom of the basket.

Has anyone else experimented with a puck screen below the puck?

Haven't done that, but I can imagine that there would be few if any advantages to placing a puck screen the puck, either with or without another one in the usual place above the puck...and many possible disadvantages, including what I think is the most significant problem that it would affect resistance to outflow through the puck during extraction (mostly increasing resistance in an inconsistent and hard to predict way as the screen gets clogged with coffee over the course of extraction). You'd essentially be adding a hard-to-determine variable into coffee making and unnecessarily complicating the whole process. You may have been lucky in getting what you felt was an improved cup using your technique. Just my humble opinion, and who knows...you may have stumbled onto something useful, so feel free to keep experimenting!

Why? I get the screen above the puck and why some use it. Are you trying to restrict the flow for a ristretto? A better way to do this would be to grind finer or tamp harder if you are as fine as the grinder will produce. Seems to me the screen below would probably just occlude the baskets holes since you won't be able to line the screen holes and the basket holes exactly.

Actually the screen lowers resistance as it removes the bottleneck that is the finely ground coffee immediately above the filter basket holes. The puck screen below enables water/coffee to exit from the entire puck bottom instead of just these areas. Consequently, a much finer grind is needed.

I've not found shots produced this way to be universally better. They have a much higher extraction (I assume, I haven't got around to measuring yet) but tend towards overextraction unless pulled with short yield and duration. And while I get much better flavour separation they seem to have an unpleasantly muddied or almost gritty "base". It changes lighter roasts to be more akin to medium roasts.

I've only tried on my major with OEM burrs. I have 64mm cast burrs on the ways which I'm looking forwards to trying the method on.

nisb wrote: Actually the screen lowers resistance as it removes the bottleneck that is the finely ground coffee immediately above the filter basket holes. The puck screen below enables water/coffee to exit from the entire puck bottom instead of just these areas. Consequently, a much finer grind is needed.

Are you just guessing this is the case or do you know it and if so, how?

Your description sounds more like you are fighting channeling in your puck despite the puck screen. Or possibly you have a poorly punched basket. That happens more often than you would think. Look through the empty basket holes at a light it will show you if you have blocked or never punched holes.

Puck screens aren't a magic bullet. They are good at keeping your group head cleaner and keeping gushers in check if your machine pushes water hard at the start. But beyond that I am highly skeptical about the other claims about them.

Is the 51mm screen actually meant to go in the bottom of the basket, or was it just a happy coincidence?

I've been using precision-cut disposable filter paper on the bottom of my 58mm basket (in addition to another filter paper on top of the puck). I've observed the filter paper producing an initial bit a flow resistance that I think helps the puck saturate more uniformly during preinfusion - which in turn can increase extraction. Furthermore, although it doesn't mitigate channeling, it does completely stop the portafilter from spray-painting the area around the cup with coffee jets.

Pressino wrote:Are you just guessing this is the case or do you know it and if so, how?

Like any statement by anyone about what is going on in the puck it is an assumption based on what can be observed - here a consistent need to grind finer.

Kaffee Bitte wrote:Your description sounds more like you are fighting channeling in your puck despite the puck screen. Or possibly you have a poorly punched basket.

Why would you think so? The ims basket is just fine

GDM528 wrote: Is the 51mm screen actually meant to go in the bottom of the basket, or was it just a happy coincidence?

It was bought with this purpose, to emulate a paper filter without the thinner body.

Pressino wrote:
Are you just guessing this is the case or do you know it and if so, how?

nisb wrote:Like any statement by anyone about what is going on in the puck it is an assumption based on what can be observed - here a consistent need to grind finer.

OK, so you're guessing. That's fine, of course.

nisb wrote:but tend towards overextraction unless pulled with short yield and duration. And while I get much better flavour separation they seem to have an unpleasantly muddied or almost gritty "base". It changes lighter roasts to be more akin to medium roasts.

What's the result of pulling with shorter yield?