Clean an oven regularly because accumulated grease and burned-on residue cause smoke and odors every time it is used. For manual cleaning, a paste of baking soda and hot water is sufficient. Some ovens have a cycle called pyrolytic self-cleaning: the oven heats itself to a very high temperature and turns residue to ash, which is then wiped away. During the pyrolytic cycle, the oven must be empty and the kitchen ventilated.
What builds up inside an oven is mostly splattered grease and food liquid that has boiled over. Each time it heats, this residue cooks again, darkens, and eventually becomes a hard layer stuck to the surface. As the layer thickens, it produces smoke and a burnt smell during each use, and the odor transfers to food. Grease that drips onto the oven floor also puts strain on the lower heating element. That is why you should clean the oven after food has boiled over or splattered, once the oven has cooled, rather than waiting for heavy buildup.
Baking soda is the easiest way to clean an oven by hand. Mix a few tablespoons of baking soda with a little water to make a paste, and spread it over the oven door glass and interior surfaces; do not apply it to the heating elements or fan cover. Leave the paste for a few hours, or overnight if possible, then wipe it away with a damp cloth and rinse. Repeat the process on stubborn spots. If you heat the oven for a few minutes and then turn it off, the warm surface releases dirt more easily; do not clean the oven while it is hot. Clean the oven glass with the same paste, wiping from the outside toward the inside.
The pyrolytic cycle lets heat do the work. The oven heats itself to around 450–500°C / 840–930°F, burning the organic residue inside at that temperature until it turns to fine ash. When the cycle is finished, the oven cools, the door lock releases, and the ash is wiped away with a damp cloth. The cycle generally lasts 1–3 hours. Empty the oven completely before starting pyrolysis: remove the racks, trays, rails, and thermometer, because most accessories cannot withstand this temperature and will change color permanently.
A few rules apply during pyrolysis. Ventilate the kitchen and open a window; the cycle produces smoke and a sharp odor. The oven door is locked while it is running and cannot be opened, and the exterior gets very hot, so keep children and pets out of the kitchen. In homes with pet birds, move the cage to another room. Use the cycle only as often as the manufacturer specifies; frequent pyrolytic cleaning is known to wear out the gasket and electronic components. Remove large pieces of residue with a spatula before starting the cycle.
Wash the racks, rails, and trays separately. Soak them in a sink or bathtub in hot water mixed with dish soap and baking soda; wait half an hour, then scrub them. Oil that seeps between the two layers of oven glass may require removing the door; follow the steps in the manual. After cleaning, heating the empty oven for a few minutes and ventilating the room helps drive off any remaining odor and moisture. Wipe the gasket only with a damp cloth; do not scrub it with any cleaner. When cleaning is finished, leave the oven door ajar for a while.