Grease from the food you have cooked has burnt onto the oven compartment.
Use an oven cleaner after every cooking process to remove burnt-on grease. If you do not, the grease can burn onto the surface of the oven compartment during subsequent cooking processes and residues will become very difficult or even impossible to remove.
For thorough and gentle cleaning of your steam oven, we recommend Miele products which also care for your appliance at the same time.
