Channeling

Channeling happens when water finds a low-resistance path through the coffee bed and rushes through it instead of soaking the whole puck evenly. Once a channel opens, more water follows it, starving the rest of the bed.

The damage is two-sided. The grounds along the channel get blasted with too much water and over-extract into bitterness, while the surrounding grounds barely get touched and under-extract into sourness. So a channeled shot can taste sour and bitter at the same time, which is confusing because adjusting one dial alone never fixes it.

It is most talked about in espresso, where high pressure exposes every flaw, but it can occur in any percolation brew. Common causes are uneven distribution, cracks in the puck, clumps, an inconsistent grind with too many fines, or sloppy tamping. The cure is better puck prep: distribute evenly, break up clumps, and tamp level. See channeling-causes-fixes for the full diagnosis.