To get rid of a microwave's burnt smell, microwave a solution of vinegar and water on high power for five minutes, and let the solution steam the inside of the microwave for 10 minutes. Then, wipe the interior of the microwave clean with a damp cloth. Be very careful when removing the hot solution from the microwave.
If the burnt food smell persists following basic cleaning, leaving a box of baking soda inside the closed microwave oven overnight is a simple solution. Heating moistened coffee grounds in the microwave is another alternative for odor removal. Place 2 tablespoons of coffee grounds in a microwave-safe bowl, and cover it with 1/2 cup of water. Microwave the mixture for three minutes on high to help rid the microwave oven of the persisting burnt food smell.
A secondary method of odor removal requires a sponge, vinegar and baking soda. Soak the sponge in vinegar, and sprinkle the surface of the sponge with baking soda. Place the dampened sponge in the microwave, and heat it for 20 to 30 seconds. Wearing gloves to protect the hands from the heat, clean the interior surfaces of the microwave using the heated sponge. Do not forget to wipe down the inside of the door as well.