Remove the oven racks. Place them in a sink filled with hot, soapy water to soak.
Saturate a cleaning rag with ammonia. Lay the wet rag over the burnt-on food and allow it to soak for 30 minutes.
Remove the ammonia-soaked rag. Wipe out as much of the burnt-on food as possible, using a clean rag soaked in hot water. Rinse and wet the rag with fresh water as often as necessary.
Sprinkle any remaining burnt-on food residue with enough baking soda to coat it completely. Scrub up the remaining residue with a fine steel wool pad.
Wipe out the oven with a clean wet rag, removing all the scum and loosened food residue. Wipe the oven dry with a clean rag.
Scrub the oven racks with a dish scrubber or a steel wool pad. Rinse with clear water, dry, and place the racks back in the oven.