Channelling

Also known as channeling

What is channelling in coffee?

Channelling happens when water finds an easy path through the coffee bed instead of flowing evenly through all of it. Part of the coffee over-extracts while the rest under-extracts, giving a sour and bitter cup at once. Even distribution and gentle pouring prevent it.

In espresso, channelling is often caused by clumps or an uneven tamp; in pour-over, by pouring onto the paper or disturbing the bed.