A bottomless — or naked — portafilter has no spout and no base, so the bottom of the basket is exposed.
What you can see
Channelling. Jets spraying sideways, or one area flowing while the rest does not. Invisible with a spouted portafilter.
The onset of flow. A good shot starts as scattered droplets that converge into one dark stream within a few seconds.
Blonding, clearly and early.
Uneven distribution. Flow starting from one side means the tamp was tilted or the bed was uneven.
What good looks like
Droplets appear across the whole basket at roughly the same time, merge into a single centred stream — the “mouse tail” — and stay dark and steady until near the end.
What bad looks like
A spray shooting sideways — a channel. Fix the puck prep. Flow starting at one edge — tilted tamp or uneven bed. Multiple separate streams that never merge — poor distribution. Immediate gushing — grind far too coarse.
The practical value
It is the only way to know whether your problem is grind or distribution. Both produce fast, sour shots, and the remedies are opposite.
The cost
Mess, at first. A channelling shot sprays across the counter, which is itself informative.
You also lose the ability to split a double into two cups.
Worth buying
Yes, for anyone dialling in seriously. It is inexpensive and it turns invisible problems into visible ones.
Last reviewed 8 August 2026