The brown is just extraction. The trouble with spent coffee is that it is hard to really get all the extraction out of coffee. All my previous experiments in this domain had some extraction around 0.5 to 2% EY. So I don’t think it is fines migration, and I didn’t see any evidence the chalk moved deeper into the puck.

If fines did clog filter baskets, a staccato should be impossible. My previous experiment with fines migration showed, using a puck of only < 200um sizes particles, that the shot still ran very fast showing that the water is going through the coffee grinds, not around.

I’m excited to see what experiments you run as a result of my work here.