All coffee guides · Troubleshooting
Channeling happens when water flows through some parts of the coffee puck more easily than others. This produces uneven extraction and can leave a shot tasting sour, bitter or hollow. Distribution and tamping are useful places to check.
Channeling is preferential water flow through parts of the coffee bed. Differences in preparation, local resistance and the way the puck changes during brewing can contribute. It is not confined to one grind size, and grinding finer is not a universal cure.
Spraying or erratic flow from a bottomless portafilter can suggest uneven brewing. A split between spouts or marks on a spent puck are less conclusive; the outlet geometry and pressure release can also affect them. Use visual observations alongside taste and repeated measurements.
Spread the grounds evenly. If clumps are a problem, a suitable fine-needle distribution tool can help break them up. Settle and level the surface without repeatedly knocking the basket. Keep the method consistent when comparing shots.
Use a compatible tamper and press level to compact the bed. There is no need to chase a universal force value. Avoid disturbing the puck after tamping. A calibrated or self-levelling tool is optional, not a guarantee of even extraction.
Use a dose suited to the basket and inspect clean parts for damage. An excessively fine grind can also make flow less predictable; compare a small adjustment rather than automatically going finer. A different basket may change the recipe, but does not guarantee channel-free shots.
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