Put your Dutch oven on a cooking surface and fill it with 2 cups of water. Add 4 tablespoons of baking soda.
Turn on the high heat and bring the mixture to a boil, then turn off the heat. Wait until the water reaches a temperature you are comfortable to work in.
Clean off any remaining stains with a nylon scrubbing pad or non-abrasive sponge - just stay away from pads with metal wires or anything too abrasive.