aiLabeling.aiLabelForImageAltText: Stainless steel thermos on a kitchen counter with cleaning brush and baking soda.

How to clean a thermos flask: tips and tricks

Want to keep your drinks hot (or cold) without any residue? If you want to enjoy your coffee, tea and other drinks on the go, you need to clean your thermos flask. It’s not complicated or time-consuming – thanks to our tips, tricks and kitchen hacks!

Thermos flasks and travel mugs should be rinsed after every use. For a thorough clean, it all depends on your favourite drinks:

For different drinks (sometimes coffee, sometimes tea, etc.) –> clean weekly
For the same drinks –> clean monthly

This is just a rule of thumb, so trust your eyes and nose: if you see residue building up in the flask or mug, it's best to remove it straight away. Also, be careful with insulated bottles that you only fill with water: tap water leads to limescale deposits, which you should also remove.

How do you clean a thermos flask?

Thermos flasks come in different versions – made from stainless steel, with a coating, with a glass insert, etc. There are different cleaning tips suitable for each model.

Stainless steel insulated jug with a chrome handle and spout, on a white background.

Cleaning a stainless steel thermos flask

The best way to clean a stainless steel insulated flask is with baking soda. Fill the flask halfway with boiling water and add a packet of baking soda. Wait a few minutes until the baking soda stops foaming, then fill the rest of the flask with hot water. Close the lid and let it soak overnight. Afterwards, rinse with clean water.

Safety tip: Only close the lid when it has completely stopped foaming! Otherwise, the gases released during the reaction can build up.

Black thermos flask with a wooden handle on a kitchen table with biscuits and tea.

Cleaning a coated thermos flask

For a coated thermos flask, use dishwasher tablets. Put one tablet in the flask and fill to the brim with warm water. Close the lid and leave the cleaning agent to work overnight. Afterwards, rinse with clean water.

Person filling a copper water bottle from a tap in a kitchen sink.

Cleaning a vacuum flask with a glass liner

Denture cleaner is ideal for cleaning vacuum flasks with a glass liner. Place one tablet in the flask and fill with warm water. Leave the cleaner to work for approx. 10 minutes, then rinse the flask out with clean water.

Extra tip: Don't forget to clean the lid of the thermos flask. Simply soak it in lukewarm water with one of the recommended cleaners or some washing-up liquid. If possible, remove any sealing rings and clean them separately. An old toothbrush is great for getting into the grooves.

Cleaning a thermos flask with household remedies: What works and what doesn't?

Salt:
Fill the flask to the brim with hot water and add 2 tbsp of salt. Close the flask and shake vigorously. Leave the thermos flask to stand overnight.
Rice:
Fill the flask halfway with warm water, then add a drop of washing-up liquid and a handful of rice grains. With the lid on, give it a good shake – the rice will help remove any residue.
Potatoes:
Add a handful of potato pieces or peelings to the flask, fill with water, close it and shake vigorously. After approx. 15 minutes, you can empty the flask and rinse with clean water.
Lemon:
Fill the jug to the brim with boiling water, add the juice of half a lemon and leave it to soak for 15 minutes. Then, pour the water out and rinse.
Vinegar:
Add 1 tbsp of vinegar to the jug, fill with warm water and leave the mixture to soak for at least a few hours, or overnight. Afterwards, rinse with clean water.

	Stainless steel vacuum flask	Coated vacuum flask	Glass-lined vacuum flask
Baking powder/Bicarbonate of soda	✓	X	X
Dishwasher tablet	✓	✓	X
Denture cleaner tablet	✓	✓	✓
Salt	✓	X	X
Rice	✓	✓	✓
Potatoes	✓	✓	✓
Lemon	✓	✓	X
Vinegar	✓	X	X

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