Food rotting because of a power outage is one common cause of bad smells in freezers. Unpleasant sour or musty freezer odours, however, may still develop also even if no outage occurred and food has remained frozen. Placing baking soda or another odour neutraliser in the freezer may help for a while, but in many cases, the bad smell will return unless you clean the freezer. Proper cleaning with the right product should get rid of bad freezer smells -- in some cases, you may have to clean more than once, however.
Remove all items from the freezer. Place frozen food you wish to keep either in an ice chest full of ice, or another freezer if available. Many kinds of foods should not be thawed and refrozen -- so make sure the foods remain frozen while you clean the freezer.
Unplug the freezer and allow it to defrost. Some new freezers may not have any ice accumulation because they have an automatic defroster. Older freezers, however, may have heavy ice accumulation. Ice can hold onto odours, so you should allow it all to melt.
Pour 1 qt. of white vinegar into a clean bucket. Add a quart of water.
Scrub the freezer interior with a sponge saturated with this cleaning solution.
Keep the freezer door open and allow the interior to air dry.
Pour at least 85.1gr. of loose activated charcoal in a baking pan or a dry, empty ice cube tray. Place this in the freezer for eight hours to neutralise any remaining odour.