When coffee has been allowed to sit in a thermos, even just for a few hours, the coffee odor may linger even after repeatedly washing with soap and water. Removing this odor to refresh your thermos requires only a simple household ingredient.
Rinse the thermos with clean water.
Pour 1 tsp. of baking soda into the thermos.
Fill the thermos with hot tap water. Loosely put the lid on and allow the water and baking soda mixture to remain in the thermos for at least 30 minutes, or longer for better results.
Rinse out the thermos and the lid with warm water. Let the interior of the thermos air-dry completely before you put the lid back on to store it.