Blooming with needle valve, Weber Unifilter and screen puck

Beginner and pro baristas share tips and tricks for making espresso.

#1: Post by Katran »

Hi, I'm using a LMLM with the needle valve mod, and with Weber's unifilter with a screen puck. I'm also stacking up 2 layers, finer grind first then coarser. I'm getting excellent (if not incredible) results with light roasts, with blooming for 30 seconds. I was watching a recent video by Sprometheus and he mentions that the discharge valve will get turned on right after the preinfusion phase, and that might suck back some of the water and potentially some of the puck. My pucks stick to the unifilter very well (by design I think, ie, the walls are straight, not tapered as in normal baskets). Moreover, the screen puck will help keeping the puck undisturbed, I think.

Is there anything to worry about, with the discharge valve being turned on right after the preinfusion phase?



#2: Post by GDM528 »

When I tried this with my Gaggia Classic Pro, the puck resistance dropped significantly, and the shot ran fast and tasted under-extracted. I postulate the rapid discharge caused the puck to 'piston', crack, and form severe channels. The discharge process probably varies between machines - for the Gaggia it's pretty violent. The effect is pretty apparent when looking at the flow pattern on the bottom of the basket.