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Channeling happens when water finds easier routes through an espresso puck instead of moving evenly through the coffee. The result can be confusing: a shot may taste sour and bitter at the same time, or change dramatically despite the same grinder setting. Preventing it is mostly about creating an even bed and avoiding damage before the pump starts.

Use a dose that fits

A basket has a useful dose range. Too little coffee can leave excessive space above the puck; too much can bring the coffee too close to the shower screen or make preparation awkward.

Use the basket's guidance and the machine's requirements as your starting point. Different coffees occupy different volumes at the same mass, so do not assume one dose fits every bean equally well.

Check that the basket is clean and its holes are clear. A damaged or heavily obstructed basket can complicate flow even when the grounds are prepared carefully.

Distribute throughout the bed

Clumps, empty pockets, and uneven filling can create density differences below a tidy looking surface. Transfer the grounds gently and spread them across the basket rather than leaving a tall mound on one side.

If clumping is obvious, a suitable thin needle tool can help break it apart. Work through the depth without repeatedly digging channels of your own. Finish with an even surface.

Avoid relying exclusively on a tool that smooths the top. A level appearance does not guarantee uniform density beneath it.

Tamp without disturbing the result

Support the portafilter securely and press the tamper level. The aim is an evenly compressed bed, not a contest to apply the greatest force.

After tamping, avoid knocking the portafilter or tapping its side. Those impacts can loosen the puck at the wall or create cracks.

Clean the rim and insert the portafilter smoothly. Start the shot promptly according to your usual workflow, rather than leaving the prepared puck sitting in a hot group while you search for a cup.

Watch for clues without overreading them

A bottomless portafilter may reveal sprays, uneven streams, or areas that begin flowing at different times. These observations can help, but an attractive extraction is not proof of perfect internal flow.

A sudden acceleration during the shot can also be informative. Compare it with the taste and repeatability before concluding that every change in stream shape is a fault.

The spent puck is limited evidence. Holes or wet surfaces can form during pressure release or removal, so avoid rebuilding the recipe solely from the puck's appearance afterward.

Keep grind within a workable range

Grinding very fine can make the puck resist flow so strongly that water favors small weak spots. If the shot is slow, uneven, and harsh, moving slightly coarser may improve uniformity.

On the other hand, very coarse grounds may allow a fast, weak extraction. Find a setting that works with the dose and yield rather than trying to solve every issue through preparation alone.

Hold the dose steady while testing grind. Changing both makes it harder to tell whether the puck structure or resistance improved.

Repeat a short preparation routine for several shots before adding accessories. Screens and paper can alter water movement, but they do not replace an evenly filled basket.

A successful change should make the flavor more coherent and the shots more predictable. The best evidence is not a flawless video of one extraction; it is a series of cups that remain sweet and balanced when you repeat the same simple preparation.