What Causes Burn Marks in the Back of a Microwave?

Metal

• One of the most common causes for a scorched microwave back is metal left in the microwave during activation. While the microwaves excite the water molecules in food, the same waves are reflected back when directed at metallic objects such as cooking pans, forks or foil. This reflection causes feedback that translates in the microwave chamber into arcing, sparking and other forms of electrical discharge. The result is either one or several markings that show where the electricity burned the side walls.

Broken Enamel

• While most of the metal-causing problems in a microwave come in the form of foreign objects, such as forks, pans and metal staples in fast food boxes, microwave chambers are made, primarily, of the same types of metal. What makes the chamber safe for cooking is a thin layer of plastic enamel. This layer shields the metal from microwaves while the metal ensures that microwaves remain in the chamber. If even a small amount of this enamel is chipped or damaged, the metal in the microwave can start to cause the same problems as metal brought in with the food being cooked. Microwaves that have damaged enamel are non-repairable and require replacement.

Crumbs and Splatter

• During the cooking cycle, foods such as spaghetti or foods with sauces can splatter material onto the microwave walls as they heat. Leaving this food material inside the microwave will subject it to further cooking each time the microwave is used. Eventually, the food particles will carbonize and even create burn marks on the sides and rear of the oven. These marks are removable with soap, water and baking soda.

Burned Food

• Burning food in a microwave is more difficult than burning food in a pan or stove, but it is possible. Cooking for long periods can lead to carbonization of the surface of the food, which leaves markings in the microwave since the food emits smoke as if it were being scorched in a real fire. If food was burned in your microwave, check with a service technician before using the microwave again since the smoke may damage the inner workings of the microwave.