It's best to prevent caked-on grime by cleaning the oven as soon as spills happen. Wait until the oven has cooled completely, then spray the inside with plain water, thoroughly saturating the sides, racks, and inside of the door before wiping clean. For greasy messes, spray the inside with a mixture of nontoxic dish soap, using one part soap, nine parts water. Then wipe everything down with a clean microfiber towel, which grips and lifts spills.
For stubborn spots that won't budge, use the self-cleaning function offered by most models. The oven heats to a whopping 900 degrees and incinerates all spills and food particles; wipe up the remaining residue with a damp cloth. The process usually takes about three hours. Self-cleaning is nontoxic (no caustic cleaners needed), but with the oven at such a high temperature for so many hours, it wastes a lot of energy, so use it sparingly-not more than once a year-and after you've already cooked something in the oven. With the appliance already hot, it uses less energy than it would going from zero to 900 degrees. If you don't have a selfcleaning oven, buy or rent a steamcleaning device (available at most hardware stores) to blast grime.
To prevent spills in the first place, place casseroles and ovenproof dishes on small baking sheets: Any sauces that bubble over won't spill onto the inside of the oven. Also, don't cover oven racks with aluminum foil-it reduces the flow of heat and increases cooking time (and energy use).
-Danny Seo, environmental lifestyle contributor for The CBS Early Show and author of the Simply Green (Collins, 2006) book series.