Channeling
When water finds a path of least resistance through the coffee bed, extracting unevenly.
If the grounds are unevenly distributed or tamped, water carves channels through the weak spots and barely touches the rest. The result is a shot that is both sour and bitter at once.
Even distribution before tamping is the main defence against channeling, which is why distribution tools and technique matter.
Why it matters for small spaces
Channeling explains why two shots from the same machine can taste very different, and why technique often beats spending more on hardware.