How can the smell of burnt coffee be removed from a microwave?

Someone in our office had a coffee disaster in our office microwave last week. Apparently they were heating some coffee and burned it badly. The white interior of the microwave is now permanently stained with a tan color on the bottom because of the volume of coffee—and the burn. I don’t care about the color, but the stench of burnt coffee lingers in the appliance.

How can this be rectified, short of buying a new microwave? (No GAs for answers that involve “buy a new microwave”.)