Bitter is the most common complaint. It means you're over-extracting—pulling too many bitter compounds from the beans. This happens when your grind is too fine, your water is too hot, or your brew time drags on.

The fix is simple: coarsen up your grind a notch, or let your water rest 30 seconds after boiling. If you're using a gooseneck kettle, you can also pour a little slower—fast pouring can cause over-extraction because water sits on the grounds longer.