Grease from your food has burned onto the oven compartment.
Remove the burnt-on grease after every cooking process using a grease remover. Otherwise, this grease can burn onto the surface of the oven compartment during the next cooking process and can be very difficult or impossible to remove.
For thorough and gentle cleaning of your steam oven, it is recommended to use Miele products which also care for your appliance at the same time.
