The idea behind this old cleaning trick is steam. Instead of immediately attacking baked-on grease with heavy scrubbing, you use hot water to soften the grime first. Place an oven-safe baking dish filled with hot water on the middle rack, then warm the oven to a low temperature—around 200°F (95°C). Let the water steam inside for roughly 20 to 30 minutes, then switch the oven off and allow it to cool enough to clean safely.

Once the oven is warm rather than hot, remove the dish and wipe the interior with a damp microfiber cloth or sponge. The steam helps loosen dried food splatters and greasy residue, so much of the mess should come away with considerably less effort. For stubborn areas, a paste of baking soda and a little water can be applied gently before wiping everything clean.

One important warning: don’t put laundry detergent caps, dishwasher pods, plastic containers, or other non-oven-safe items inside a hot oven. Viral cleaning photos sometimes show these products sitting in dishes, but heating detergents or plastic can release irritating fumes, melt materials, or damage the appliance. Plain water is enough for the steam portion of the trick.

For extremely dirty ovens, steam won’t magically remove years of carbonized grease in minutes, but it can make the job much easier before normal cleaning.

So Nana’s basic idea still holds up: let heat and moisture loosen the mess first, then wipe instead of scrubbing for ages.