How To Clean A Coffee Thermos? (Helpful Tips)

Last Updated on July 19, 2023 by Barry Gray

I love my thermos. It’s my go-to companion for long days out and about. I admit I am a high-energy person and am only happy when I am out and about doing ‘stuff.’ 

Whether hiking, driving across town, or camping, I am always on the go. 

Using a thermos can call for some serious cleaning, and further on in this article, I will mention a few you are bound to love. I keep things as simple as possible, so if these work for me, they will work for you. 

The best way to clean a coffee thermos is to clean it as soon as you are finished. Use warm soapy water, a denture table, or a vinegar/baking soda combo. Any of those options will not only get your thermos clean, but it will also be free of any old coffee that could taint your next brew.

I know some people may have other cleaning methods that are their favorite, but those three options are the ones I’ve found to get the best results.

Plus, I will be giving you a tip on how to remove stale smells from a thermos. Nothing is worse than having soup in your flask and then switching to coffee only to notice that the thermos smells strongly of chicken noodles!

But here’s the cool thing.

Care for your thermos, and I promise it will last for years.

how to clean a coffee thermos

Caring for Your Coffee Thermos

One of the easiest ways to keep on top of your flask, which means better performance, is to clean it after each use. 

Only leave liquids in there briefly if you can help it. I have my own favorite trusty hand-washing devices for this. 

Like many people, my coffee thermos is my trusty companion and has sometimes been a lifesaver for me, like the day I went camping with the promise of sunshine, and it snowed the whole day. 

I’d pitched my tent, sat down just after 7 am, and looked forward to a long hike and hot meal made over the coals I had packed away for later, but the weather suddenly changed drastically within the hour. 

The wind started howling through the trees, and the temperature dropped to around -5 degrees.

I was in the woods, alone and freezing, so I began to make a fire. I planned to get warm but remembered my coffee thermos in the car.

I cracked open the lid, poured the golden hot liquid into the cup, and had what could have been the best sip of coffee I had ever tasted. It was like a hug from the inside out. I’m sure you know the feeling. 

It began snowing and warmed a little from the coffee. I decided to go for my short hike anyway.

 It turned out to be a great day, and by the afternoon, the snow had begun falling consistently and had created a soft white blanket over the woods I was walking in. Fresh snow certainly has a certain magic about it.

From that day on, I decided I’d only go somewhere with a warm drink handy. Never mind which weather I was facing, to this day, I was happy with that choice.

Why Should You Carry a Coffee Thermos?

I always have my thermos, whether hiking, camping, or commuting to work. It’s the perfect way to keep my coffee or soup hot, no matter how long I’m away from home.

I’ve had my thermos for years, and it’s still strong. 

It’s been dropped, bumped, and knocked around but never once leaked. The insulation is top-notch, and my drinks stay hot for hours.

Over the years, I’ve purchased real duds for flasks and travel cups. I was at a point where I’d pick one up if I saw it at the checkout! 

That is probably not the best practice. 

Not all thermos flasks or mugs are the same. Like everything, it’s a learning curve.

The thing is, once you have an excellent flask, you have to know how to look after it. Keeping it clean and checking for scratches and bumps is essential. If you don’t, you won’t be rewarded with that golden hearty liquid whenever you feel like it. 

How Do You Clean Your Coffee Thermos Effectively? 

Let me tell you one thing I simply cannot stand. Marks in cups or on crockery. 

Honestly, it drives me insane, and I’m not the biggest clean freak out there.

Seeing stains left behind long after I’ve polished off the last mouthful of my coffee and washed my thermos makes me feel I didn’t do a good enough job. I know it’s just marks, but it gives me the impression that things are not as clean as they should be.

I’ve tried a few methods over the years to remove those stains and to feel my coffee thermos is indeed as clean as possible. Some have worked better than others, but here are the cleaning methods that did deliver the best results.

The salt and ice method

I use store-bought ice; I place it in a dishcloth and hammer it with a food tenderizer, making it a little smaller than it already is. 

I pour the ice into the flask, add some coarse salt (like kosher salt), and shake like crazy. The salt acts as an exfoliator for the inside of the flask, removing stains and built-up residue. 

Once you have shaken enough, pour the ice and salt out, rinse well, and leave it to dry.

I picked up this method via a friend some years ago and admit I doubted it would work. However, it does a pretty good job, and it’s a method I use often.

The baking soda and vinegar method 

There is this crazy cleaning chemical reaction when adding vinegar and baking soda. It’s pretty freaky the first time you see it happening.

For the scientist in you – here is why vinegar and baking soda works. If you are not interested, then skip this paragraph. 

This process is a double displacement reaction, which means that the ions of the two reactants are exchanged to form two new products. 

In this case, the sodium ion from the baking soda (NaHCO3) is exchanged with the hydrogen ion from the vinegar (CH3COOH) to form sodium acetate (NaCH3COO) and water (H2O). The carbon dioxide gas (CO2) is produced as a byproduct of the reaction.

This reaction often produces many foamy bubbles in science experiments and demonstrations.

It can also be used to clean surfaces, as the carbon dioxide gas helps to loosen dirt and grime.

I have used this method to unblock drains, which will tell you how good the technique is. Plus, it is safe as you are using non-toxic ingredients. 

How To Use The Vinegar and Baking Soda Mixture

All you do is pour the vinegar and baking soda into your flask; use 1 part vinegar to 2 parts baking soda. 

Once the fizzing has stopped, fill the thermos with hot water and place the cap back on. Give the flask a gentle shake, then leave to soak. 

After about fifteen minutes:

  1. Pour the mixture out and rinse well; use a special flask cleaner brush to hook out the last stains if required.
  2. Leave to dry.
  3. Rinse well will get any leftover vinegar smell or taste.

However, when I make a new flask of coffee, I usually pour hot water into it before adding liquid. It gives it an extra rinse to ensure no remnants of the mixture are left behind.

The Denture Cleaning Method 

This is a genius way to clean your flask and is non-toxic. 

Fill your flask with warm water, then toss a denture tablet inside. Once it has stopped fizzing, get a bottle washer and swish around inside. 

Empty the dirty water and rinse. If you feel it is not clean enough, repeat until all the stains are gone.  

Warm Soapy Water 

Whenever I use my thermos travel cup or flask, I wash it well when I empty the last dregs of coffee down the sink. I rinse well, then wash with a cloth and soapy water. 

This helps to keep the stale tastes of old coffee coming through to my next drink. 

I also use a few bottle washers to help with the task. 

Some have soft bristles, and some are just made of sponges with a long handle attached. If you are cleaning a cup, you can use a small sponge. 

Also, check if your thermos is dishwasher safe. For those that are, I cannot recommend using a dishwasher enough. A thermos does get a strange taste over time if not cleaned properly. It hangs on to old flavors and tastes; a good wash will eliminate this. 

How to Remove Smells From Your Coffee Thermos

baking soda to remove smells from coffee thermos

If you feel that there is still a strange smell after washing your thermos, add baking soda to the water, leave it to soak for half an hour, then rinse and clean. Baking soda is an excellent deodorizer. 

Also, it contains no toxins, so you have no reason to worry about any strange tastes or what you are consuming.

My Recap on Cleaning a Coffee Thermos

Keeping your coffee thermos clean is easy, so here’s a quick recap of the main points I’ve covered.

  • Wash after every use to keep your thermos clean
  • Use salt and ice and shake to help remove stubborn stains
  • Baking soda and vinegar together works well for cleaning
  • You can use a denture tablet to clean your thermos
  • Warm soapy water is best
  • Check if it’s dishwasher-safe before throwing it in

Cleaning your coffee thermos should not be difficult at all. It takes minutes, but the enjoyment and pleasure you get from your coffee will last substantially longer. 

My Conclusion

Getting into the habit of cleaning your thermos after every use is important. It stops those stains and general grime from building up and potentially ruining your coffee.

The best thing to do is try a few methods and see your results. It would help if you settled on one that works for you. 

I often use the vinegar and baking soda method, and if the thermos is smelly, I do the baking soda deodorizer trick. Sometimes I make robust coffee and need this little extra step. 

If you use one of the methods listed above, I promise your coffee thermos will be as good as new, allowing you to enjoy your coffee for years to come.