How to Clean a Thermos Flask: 10 Tested Methods

Tips and Tricks

I own 7 thermoses.

And I can tell you for sure: there is no one universal way for thermos cleaning. It all depends on the food you store there, the material your thermos made of and the time you let your thermos stay dirty.

For example, if you an attentive owner of a coffee thermos, you’ve probably noticed that mold over the upper portion of the thermos. And those old coffee stains on your stainless steel mug.

Yeah, that’s it…

A dirty thermos can not only contain dangerous mold but also an inhibit bacterial growth and metallic taste. If it’s not cleaned on time, it can be really dangerous for your health.
For this, I prepared a list of the most popular & effective ways to clean your thermos. Both organic and non-organic (for those of you who are already desperate to fight bloom, odors, etc.).

1. Baking soda

cleaning thermos with baking soda

This is a great, cheap, always-on-hand method to clean literally anything in your thermos, including lid. Used alone or in combination with a vinegar it delivers more than good result.

Now, use 1” of vinegar (cider is the best), add 1 tablespoon soda and warm water for every 2-3 full cups that your thermos holds. Let it do all the dirty work for a while, then scrub & rinse well.

This solution is definitely better than just soap with water or simple Comet that leaves scratches. And it doesn’t have any odors.

2. Hydrogen peroxide

cleaning thermos with hydrogen peroxide

You can use it as a vinegar substitute together with soda. It works perfectly well for food thermoses, sometimes even better than the vinegar alone. The only thing: don’t overuse it.

3. Vinegar

cleaning thermos with vinegar

Using it alone will bring you a terrific result in removing stain from your coffee or soup thermos. Together with warm water or a couple of ice cubes – will do the job too. Put vinegar together with warm water or ice cubes, shake it for a few moments, scrub the walls with a brush (or use simple rice instead), rinse and let it dry.

4. Soured milk

cleaning thermos with soured milk

Yeap, soured milk. I’ve used it for a while when I had meals with a really fat mutton and didn’t have any other cleaning option. You might try it as a plan B when time will come, because until now no one has ever believed me that soured milk can actually be a good thermos cleaning solution.

5. Lemon juice

cleanign thermos with lemon juice

I guess you know that lemon juice is highly helpful when it comes to scaling. It’s also an amazing helper when it comes to cleaning thermoses. Use it as you usually do it with your kettle.

Also, it’s a perfect way to get coffee smell out of your thermos.

6. Dishwasher soap

dishwasher soap for cleaning thermoses

In order not to damage the walls, it’s better to use the liquid one. Never leave the cup full of water & soap for more than a couple of hours. Better clean it at one go and leave it to dry.

7. Dish detergent

clean thermos with dishwasher liquid

Same as with dishwasher soap. Check Dip it as well.

8. Denture cleaning tablets

cleaning thermoses with tablets

Use it adding a good portion of warm water (hot is the best), don’t put the cap on and let it be there for some time. After it’s finished, rinse carefully and repeat the process if needed.

9. Ice and salt

cleaning with ice and salt

This combination works as a scrub. The very important thing here is to not use big ice cubes because they simply can leave the scratches.

Add a couple of tablespoons salt, cap on and shake until the ice melts.

10. Essential oils

cleaning with essential oil

Put 2-3 tablespoons of tea tree oil together with warm water. This option is great because you can leave this mix overnight and nothing bad happens to the surface.

Rinse with soapy water in the morning and let it dry. The only minus is that tea tree oil has a strong odor.

Eva Esi
Eva Esi
Leave a Reply

  1. Avatar
    Ken Kern

    How does one go about cleaning coffee stains off the silicone gaskets in the Thermos 16 ounce King tumbler?

    1. Eva Esi
      Eva Esi author

      I would suggest dipping an old toothbrush in the mix of vinegar and baking soda. Use this to brush gaskets and then wash it with warm water. I hope it helps!

  2. Avatar
    angela westcott

    Just bought a new thamos Flask but cant get a smell a way done bicarabonta over night but still got smell please can you help me

  3. Avatar

    I tried everything!!!! Nothing worked & then it dawned on me… BLEACH!!!! Worked absolutely flawlessly!!! Inch or two of bleach in the bottom mix in hot water till half full and shake!!!! Rinse thoroughly!!! My thermos now looks and smells better than new!!!!