drdna wrote:
Problems I see with this approach: the added flow restriction of the filter paper will affect the flow rate of the espresso and change the overall extraction profile. The sides are unsealed, so the water may be forced to channel around the filter paper. It won't keep coffee oils from getting to the screen, which will still need some maintenance.
Well, based on my limited observations I think the use of a poly-felt filter may become a fixture in my shot-pulling routine.

Here's what I did:
Using a Cremina filter basket, I lightly traced a circle on the poly-felt material. Then, I cut inside the circle to fit in the basket. Following my usual routine of grind, WDT, Stockfleth, Staub tamp I placed the poly filter on top of the puck and pulled my shot (SM Liquid Amber). The shot was thick and creamy with the same characteristics as my subsequent shot without the poly filter.
The major difference is that after using the poly, the were virtually no grinds in the grouphead. I still performed my cleaning routine with a grouphead brush, wet paper towel and a cleansing flush to purge the oils.
I performed an identical routine using a poly filter cut to fit a standard 58mm basket for my Sirena semi-auto (Big thanks to Roastarama for his terrific tutorial!). I grind a bit finer for the Sirena but the shot came out fantastic. Loads of crema and full of fruit and sweet, smoky caramel. Flavor profile was identical to the shot pulled without the poly filter on top of the puck.
There was, however a difference in post-shot cleanup from the Cremina. With the Cremina, the puck was solid and the poly filter was completely dry. With the Sirena, the poly filter was stuck to the grouphead and the puck was slightly soupy. This may be a result of the Sirena not having a three-way solenoid. There were a FEW grinds left on the grouphead but I think perhaps that was due to me cutting a little too much inside the circle that I traced on the poly.
Anyway, my extremely early conclusions lead me to believe that using the poly filter greatly reduces grind retention residue on the grouphead. I'll still follow my regular routine of flushing the grouphead but like the OP, I usually flushed two or three times to clean after pulling a shot. Now, I only have to do one short flush. The poly filter seems to not restrict flow extraction and thus not alter flavor profile while simultaneously greatly reducing post-shot clean up.
I admit that my cupping skills are probably not up to most folks on this forum however I'm pretty sure I can taste the difference in an "apples to apples" comparison where the only variance is the poly filter IMOHP.
Questions? Suggestions?
Steve, in Ft. Worth