How do shower screens get so nasty? I've never seen anything more than the tiniest bit of coffee grunge on the inside of mine, and I don't backflush with detergent and remove the screen very often. I do a portafilter wiggle and wipe the screen after every shot, and regular backflush after every session. I'm almost disappointed when I remove the screen every couple months and it looks so clean it's barely worth washing.

Unsure. My results are similar. At worst, there is a tiny film with only the slightest tint of brown. I do weekly detergent backflushes and allow the group to soak for a few moments in the detergent while flushing. It could be a side effect of over stuffing a basket. I rarely fill my basket to the point the puck touches the screen. If you fill them to capacity some sludge could migrate up through the shower screen.

Bob_McBob wrote:How do shower screens get so nasty? I've never seen anything more than the tiniest bit of coffee grunge on the inside of mine

Massive overdosing? i'm not sure either, i don't have a backflushable machine anymore, but when i did it only got a detergent backflush about once a month, if i popped the screen off it always looked clean