Espresso
Diagnosing a shot with a bottomless portafilter
The cheapest diagnostic instrument in espresso. What you see in the first five seconds tells you what went wrong at the bench.
- Skill level
- Intermediate
- How long it takes
- The length of a shot
- Equipment needed
- Bottomless portafilter, Espresso basket
- Steps
- 4
Safety
Espresso leaving an uneven puck moves fast and is hot enough to scald. Keep your face clear of the underside and expect spray while diagnosing.
Why it works this way
Espresso faults are hard to diagnose from taste, because several different causes produce a similar unpleasantness. A bottomless portafilter turns most of them into something you can watch. The information is concentrated in the first few seconds — how the underside wets, where the first drops appear, and whether the streams converge — and once you know what those look like, the same faults become obvious on subsequent shots without needing to think about it.
What you need
How to do it
Watch the underside of the basket wet, rather than watching the cup.
An even, gradual darkening across the whole surface is what you want.
Note where the first drops appear.
Drops arriving from most of the surface at roughly the same moment indicates an even bed.
Watch the streams converge.
Several streams should merge into one within a few seconds and stay merged.
Treat any sideways jet as a channel and note where on the basket it came from.
The position is information: an edge jet suggests an undersized tamper or a poorly seated bed; a central one usually suggests a clump or a crack.
How to tell it worked
An even, unhurried flow that becomes a single stream with the colour of a thin caramel, without any part of the surface running clear or firing sideways.
If it did not work
What you saw, what to change, and why the change works.
A jet firing sideways from the edge
Change: Check the tamper diameter and that the bed sits flat against the basket wall.
An uncompressed ring at the edge is a channel all the way round.
One spot flowing well before the rest
Change: Improve distribution before tamping.
A less dense area lets water through early, and the rest of the bed never catches up.
Flow starts fast everywhere and thins quickly
Change: Grind finer or increase the dose within the basket's range.
The bed as a whole is offering too little resistance.
Blonde, pale flow very early in the shot
Change: Stop the shot earlier or grind finer.
Blonding means the coffee being extracted is already spent.
Common mistakes
Concluding the portafilter is faulty
The preparation fault continues unaddressed.
Instead: The spray is a symptom of the puck, not of the hardware.
Watching the cup instead of the basket
The information is in the first few seconds under the basket, and it is missed.
Instead: Get your eyes level with the underside for the first five seconds.
Diagnose a specific problem
The science behind it
- Channelling
Water finding an easy path through the coffee bed instead of flowing through evenly.
- Flow rate
How fast water moves through (or is pushed through) the coffee bed.