If you store coffee in your thermos regularly, it’ll eventually develop coffee stains. These stains make other liquids stored in the thermos to have a stale and odd coffee taste. The best way to eliminate the stale taste is by eliminating coffee stains from your thermos. That way, you’ll enjoy fresh-tasting liquids when stored in the flask, be it coffee or any other liquid.
Add hot water into the thermos until full. Add a denture-cleaning tablet into the thermos. Allow the tablet and water to sit in the thermos for about 4 hours. If the coffee stain is stubborn, allow the thermos to soak for some extra hours. Empty the thermos and rinse it thoroughly with soapy warm water.
Again, fill your thermos with clean, hot water. Add 2 tablespoons of a powder dishwashing detergent. Stir the contents to allow the detergent to dissolve in the water. Allow the thermos to soak in the soapy water for about an hour or more if the stains are severe. Once done, empty the thermos and wash it with soapy warm water. Next, rinse it thoroughly with warm running tap water to remove the detergent.
Add hot water into the thermos until full. Next, add 2 tablespoons of cleaning vinegar or white vinegar. Once done, stir the contents and leave the thermos to soak overnight. Rinse the thermos and wash it with soapy warm water to remove any remnant vinegar smell. Next, rinse it with warm running tap water to remove remnant vinegar and detergent.
Warm some vinegar, preferably in a microwave-safe bottle or container. Add the warm vinegar into the thermos until full. Add baking soda (1 tablespoon) and mix the contents well by stirring. Allow the mixture to sit for about 4 hours. Empty the thermos and rinse it. Next, use a clean bottle brush to brush out any remaining coffee stains. Once done, wash the thermos in soapy warm water. Rinse it with warm running tap water to remove any remnant vinegar.
Add crushed ice into the thermos until full. Add lemon juice from a freshly cut lemon. Next, add 1 tablespoon of salt. Mix the contents thoroughly. Allow the contents to sit in the thermos overnight. Empty all the contents. Use a clean bottle brush to scrub the interior of the thermos. Allow any residual lemon juice and salt to sit in the thermos for about an hour. Once done, cleanse the thermos with soapy warm water. Next, rinse it thoroughly with warm running tap water.