Microwaves can be freshened by wiping the interior with a solution of four tablespoons of baking soda to one quart warm water. NEVER use a commercial oven cleaner
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Wet a rag with cold water, leave it really wet but not dripping. Nuke it for about a minute and then open the microwave and wipe the mess away with a separate wet cloth. The one that was microwaved is VERY HOT do not touch it with your hands. Mess will wipe away easily without ANY cleansers at all. The steam loosens the baked on mess and it wipes clean away. May need to repeat a few times before you are done.
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I put a cup of water in the microwave with a couple of tablespoons of lemon juice in it (or a couple of drops of dish soap if I'm out of lemon juice), run it for 2-3 minutes, let it sit so it steams up the inside of the microwave and loosens the stuck-on yucks, then wipe it all away with a paper towel. It's quick, simple and makes the microwave smell nice!...