Preinfusion donuts

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#1: Post by GDM528 »

I frequently observe 'donuts' during preinfusion. The ensuing shot seems fine, with no signs of channeling - but I wonder if my preinfusion is hinting that everything may not be entirely hunky-dory.

Apologies for the blurry photo, but this is an example of what I see just before cranking up the pressure:

The instant I kick on the pump the entire face of the basket saturates and appears pretty uniform. Preinfusion pressure on my machine is 2ish bars, and extraction is 6-7 bars. Perhaps the manner in which water flows through the puck is a function of the pressure?

Could this be a filter basket thing? I'm using a 18g VST ridge-less basket. The bottom of the basket is slightly domed, so the puck ends up about 1mm thicker in the middle after level tamping. VST also places holes only 2-3mm from the outer edge, which seems really close to me. Are there alternative baskets with a wider hole-free perimeter?