I've read of people using Aeropress filters in espresso prep, both below and above the puck for all sorts of reasons including filtering for cholesterol (below puck), dampening the effects of the water from the screen or dispersion block and just keeping the group clean and in some cases preventing coffee fines from entering the cylinder of levers, but now that I've been consistently using a filter above the puck on my 1950's Faema Faemina I can say that it has really helped me in keeping the grounds from getting up in the group. I've had a persistent problem with coffee grinds appearing when I flush (was hoping they were just coffee grinds) and now that I'm consistent it's resolved itself. It also keeps the group cleaner and the puck looks less disturbed by divots so I'm sold.

Not sure about the worries over cholesterol, all I've read is that a compound named cafestol present in coffee is mainly present in coffee made by steeping (french press etc) and not of any real concern in espresso. It's effect is not huge anyway, 6-8% (of your normal level... not an additional 6-8% )

My experience with the faemina is that unlocking the PF early is messy but if I have the patience to wait a bit everything stays clean though I have to admit that the firat flush sometimes brings out some old grounds..mainly when I unlocked too soon or when I forgot and the vacuum created by cooling sucked in the gunk..

Adding a picture to the thread. This was taken right after removing the portafilter from the group without any flushes or cleaning of the screen.

Scary, that IS clean are you sure you made an espresso

Interesting idea. Does the filter above the puck affect the cup result in a discernable way? I imagine it changes how the water initially wets the puck. But wondering if it makes any detectable taste difference.

I haven't noticed any impact in flavor.

Hmmm...good idea yakster! I think I'll try this with my Export as like your Faema I also think grounds are back traveling above the puck...

You guys know that grounds going into the boiler are also a sign of a damaged or worn upper piston gasket, but other readers may not know that.

^ Yes. But it happens with brand new, newly installed piston seals.

If you've installed them and lubed them and it happens brand new, then the filter's a good idea. If you have factory installed seals you might want to check and see if they've been lubed. I reviewed a new machine where the seals weren't lubed, fixed that and the coffee stopped washing into the boiler.