coffee channeling causes 2

https://future-wiki.win/index.php/The_Perfect_Pairing:_Cinnamon_Streusel_Coffee_Cake_and_Your_Morning_Brew

When coffee channeling happens, water finds a path of least resistance through the espresso puck, leading to uneven extraction and a sour or bitter shot. It's often caused by uneven tamping, too fine a grind, or clumpy grounds that create weak spots. Fixing it means a more balanced, delicious espresso.