Sourness is the opposite problem: under-extraction. The water didn't pull enough sweetness and acidity, so you're left with a sharp, tangy cup. This usually means your grind is too coarse, your water isn't hot enough (below 195°F), or you're pouring too fast.

Try a finer grind. If that doesn't help, check your water temperature—it should be just off the boil. And slow your pour down to a steady trickle, giving the water time to work.