Still sour? Let's get more precise. Grind finer—not dramatically, just one or two clicks on your grinder. Then, try bumping your coffee dose up. If you're using 30g of coffee to 500g of water (a 1:16.7 ratio), go to 33g (about 1:15). More coffee means more solubles, which helps push extraction.

Also, pour slowly in circles, starting from the center and spiraling out. A consistent, controlled pour keeps the bed even and prevents channeling, where water rushes through weak spots.