Cleaning a Thermos

By Carolyn Shearlock © 2011 • all rights reserved


It would be truly wonderful if both ends of a Thermos bottle would screw off, so you could really clean it.  (I got this idea from the Clean Bottle, a water bottle that unscrews on both ends so long distance bike racers can scrub out their sugary sports drinks).  But alas, the folks at Thermos haven’t done this.  So how to clean a Thermos?

For simple stuff, like just everyday coffee in the Thermos, it’s pretty simple:  a bottle brush (look for them in the baby department, not kitchen or housewares), dish soap and water.  Scrub some, add some more water and shake it up.  Pour it out and rinse.

OK, you probably knew how to do that.  But if you do any Thermos Cooking . . . or make yogurt in your Thermos . . . or use it to keep soup hot on watch . . . or just have been putting coffee in there every day for the last month, there’s going to come a day when you need more cleaning power.

So here are six techniques that you can use to clean that gunk out of the Thermos.  Choose whichever one you have the supplies for (I know, some aren’t items we normally have on board).  All of these work well on stainless, glass-lined and plastic “vacuum bottles.”  And yes, it’s easier to clean wide-mouth bottles — but sometimes that’s not what we have.

1.  Denture cleaning tablets. Use roughly 1 tablet for every two cups the Thermos holds.  Drop them in and add water (hot is best, but regular will work) — it will foam up, so do this with the Thermos in the sink and don’t put the cap on.  Let it sit for several hours — or overnight.  Pour some of the solution out, then use the bottle brush to scrub inside to make sure that all the loosened bits come out.  Pour the solution out and rinse several times.

Denture cleaner is designed to get bits of food and scum off dentures, and is the best cleaner I’ve ever found for a Thermos.

2 .  Dishwasher powder. Not your regular hand dishwashing liquid, or dishwasher liquid (although that is a second choice), but dishwasher powder.  Not something you normally have on board, and it can be hard to find (and expensive) in less developed countries.

Use about 1 tablespoon per quart (4 cups, 1 liter) that the Thermos holds, and add hot water.  Depending on the brand used, you may have to briefly put the cap on and shake it up — if this is the case, remove the cap carefully as pressure can build up as the detergent foams.  Leave the stopper off and put it in the sink for several hours to overnight.  Follow the rest of the instructions for using denture cleaner.

I find the denture tablets are easier to use and do a little better job of bubbling stuck on bits off, plus they’re much easier to store and use.

3.  Baking soda and vinegar. Put about 1″ of vinegar into the bottom of the Thermos (cider vinegar works best as it’s the most acidic) and add 1 tablespoon baking soda for every 2 cups that the Thermos holds.  Quickly fill the Thermos with boiling water.  It’ll foam a little but not as much as the denture tablets or dishwashing powder; the rest of the directions are the same as above — don’t cap, let sit, scrub and rinse.

This is a great fall-back method, as almost everyone has the supplies on hand.  It takes more scrubbing than the methods above, but it’s significantly better than just dishwashing soap.

4.  Baking soda and hydrogen peroxide. If you don’t have vinegar, you can use hydrogen peroxide in its place; same instructions.  Do not use lemon juice as a substitute for vinegar in a stainless Thermos, I’ve read that it can damage the welds (but I don’t know from personal experience).

5.  Baking soda. You can also use baking soda on its own as a scrubbing powder.  Pour some into the Thermos and use a bottle brush to scrub, then rinse well.  It’s much less likely to leave microscopic scratches on the liner than cleansing powder (such as Comet) — and scratches can result in cracks or corrosion.

This works better at getting stuff off the sides of the Thermos than right at the bottom — the bottle brush just doesn’t like to get at the bottom to scrub anything.

6.  Ice and salt. Fill the Thermos about 1/4 full of ice (smaller cubes work best — if your cubes are large, put a few in a plastic bag and hit with a hammer, but don’t make them too small) and add 2 to 3 tablespoons salt.  Cap and shake.  And shake.  And shake.  The ice and salt are scrubbing away at the side walls as you shake, so by twisting and turning the Thermos, you’ll gradually wear away all the gunk.  Discard and rinse.

This works, but it takes a fair amount of effort . . . and ice.

Any other techniques that work for you??

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  1. Bruce Bibee says:

    Likely only useful on glass because it will probably cause the microscopic scratches you warned against – ‘clean’ sand and seawater. Free and plentiful in our environment. A handful of sand and 3/4 full of sea water. Shake and rinse – then wash.

    • Carolyn Shearlock says:

      I think this would work well on a glass-lined Thermos, but as you suggested, I wouldn’t want to try it on a stainless one!

      Thanks, Bruce!


  2. At work we are supposed to clean the thermos-style airpots with regular dishwashing liquid (Ajax, Palmolive, etc) and we have no scrub brush. I have asked for one, but so far no luck. I have used automatic dishwasher detergent on my husband’s thermos for years when it gets too stained from regular coffee use, but I would have to buy that to use it at work. However, I recently figured out that with a clean rag, hot water and dish soap, I can achieve good enough results. I put a little dish soap in, fill about half full of hot water, get the rag wet and slide it in the thermos. Then I cap and shake, turning it over and around to make sure that gravity makes the rag “scrub” on all sides and the bottom. I can even stick the long metal pump pipe(?) into the thermos on top of the rag and use it to scrub the bottom with the rag. It is a lot of work and I only recommend it if you have good wrists. I have carpal tunnel symptoms and won’t do it this way any more because of that.

  3. Why don’t they make a scrub brush with a long strong handle that will fit down to the bottom of these things???

  4. I use C-Brite, a commercial cleaner easy to find

  5. Chilton Grose Chilton Grose says:

    I had very black greasy coffee build up in my stainless vacuum bottle. I had tried baking soda, dish washer powder, poly dent, truck bed cleaning acid nothing seemed to work. Until I tried E-Z Off oven cleaner. Soak the inside of the bottle with oven cleaner wait two hours and rinse it thoroughly. Then wash as you normally would.

  6. Tom Barrella says:

    Thanks for your article. I have what Chilton Grose has, a tall stainless steel Thermos that is staining from my wife’s Brazilian rocket fuel coffee. I did see on Bed Bath and Beyond’s web site there’s a brush that’s supposedly 14″ long. It might work. I will order it and see if it fit with enough room to hold it.

    I will also try the E-Z off oven cleaner recommendation. Thanks.

    • Michael says:

      I bought a toilet brush. New of course. It is long enough for my big thermos. Hard to get through opening first time but it softens after you get it in

  7. When I was a kid working in the fast-food industry, we used to clean out coffee pots by putting Comet and crushed ice in and swirling that round till the dirt was scrubbed out, and then washing that out with soap and water

  8. It’s probably already in your book (which I will buy soon), but could you do a write-up on cleaning out aluminum water tanks?

  9. “B-Brite” Avail. at Home Brew shops and Mail order is great for Water tanks and Thermos Bottles. Dose it at 1-2 Tbl. per Gal. (pre dissolve in warm water), then “Fill” the tanks w/ fresh water to stir it up and let it sit for 24-48 hrs.. Drain and Flush all the crap out a few times and your tanks etc. are like new inside. This is a commercial Wine/Beer Bottle, Glass, Cooking equip. or whatever else cleaner for Restaurants/Bars etc..

  10. I sailed tugs,crewboats& supply boats for 30 years! Drank lots of coffee and cleaned to pots with ice cubes! Place them inside and swirle it cleans all the stuck on oils and bits of ground coffee.

  11. I just cleaned an old Aladdin Thermos that was starting to rust around the bottom. I put in a handful of raw long grain rice, a handful of rock salt and poured in about a cup of white vinegar. I corked it up tight and slowly rotating the bottle just rocked it back & forth sloshing the mixture around for about 20-30 minutes. I know, seems like a long time but did it watching TV & it looks like new inside again. No idea how long it’ll last but dang if it’s not useable right now and it wasn’t before I started.

  12. Stainless steel Aladin thermos full of coffee stains. I cleaned it out using bleach about 4oz and the rest water. shook it up to mix and let sit over night. The next day poured some out and shook up the rest and then poured it out. bright and shiny. rinse several times until you cannot smell the bleach.

  13. I came across a product that works so well on steel thermos bottles and steel coffee makers, it makes them look brand new. It’s called “Dip-it.” A box of the powder cost about $4.00, but it’s usually hard to find in stores and must be ordered. But, a 5 ounce box lasts a long time. You boil enough water to completely fill the thermos, then, while it’s boiling, add 2 tablespoons of “Dip-it” and stir to disolve the powder. Then, using a funnel, pour into the bottle; and let it stand for 15 minutes without the stopper on the bottle. (No brush required.) Next, pour it out and rinse several times, and look inside. It will be as shiney as when it was new. And, I “always” have strong coffee in my thermos, and it gets gunky! I usually clean it 2 – 4 times per year, and the “Dit-it water” that gets poured out after 15 minutes looks like coffee itself because it’s so brown. Lol, I had spent years with a brush, ice, salt, and all those methods; and none really worked. And “Dip-it” works so well, they should market it exclusively for thermos bottles, instead of as a general “food and beverage stain remover.” The only down side is it’s hard to find in stores. there are drugstores on line that sell it for exactly, $3.99 (I just checked).

    • The best price I can find — including shipping — is on Amazon: Dip-It on Amazon. I looked at several drugstore sites (don’t know if they’re the same ones you saw) and with shipping, they’re all more.

      • Try “drugstore dot com.” It’s $3.99. They could sell it for 20 and it’d still be worth it. The only way I’ve found to really get a thermos sparkling inside (no scrubbing or even wiping — just rinse after). Bought an old Stanley for 2 bucks at a yardsale, and had it like new in 15 minutes. Shined a flashlight into the hole and it was as silver as a new one in the store. I usually get 2 boxes since it’s hard to find. Was in a small town a few hours away a few years back. Their small Grocery carried it (I couldn’t believe it). They also had the automatic drip coffee maker cleaner (a different, liquid product). I bought one of those, too, but it didn’t seem to work any better than vinagar. But the powdered Dip-it for metal sure does. It even cleans the pot that you boil the water in, even though it’s only in there for a minute while you’re stirring it as it desolves.. You’d think Walmart would carry it.

  14. Barbara Lowell says:

    I buy $1 baby bottle brushes at Dollar Tree; be sure to look for rounded bottom brushes, not flat bottom so the bristles can clean the bottom instead of the wire scraping the bottom. They also sell $1 denture cleaning tablets which work fine esp with the brush. Also have pour bleach in the bottom, poured it out into a small bowl and soaked the rim of my thermos and coffee cup in that.

    • Barbara,
      You sound like an old girlfriend I had (the one with the great legs) who used to clean my thermos (and hers) pretty much the same way you mention. And, it did work okay. The main problem was there were steaks left inside, and areas she couldn’t reach with the brush, like just under the rim, inside the bottle. And, for the same price as those materials, you can just buy “Dip-it” which works like a miracle (which I discovered later)..

      Once, when I ran out of Dip-it, I tried doing the same thing with baking soda, only about 4-5 tablespoons (instead of 2).. I waited for the water to boil, then stirred in the baking soda for about a minute. Then, poured it into the bottle and let it set overnight. (instead of 15 minutes like Dip-it). In the morning a lot came out, but not all. It would have taken another time ot two to get it “like new” but, I think it would have worked. Using your brush and denture tab method first, then, the boiled baking soda afterwards might work good.

  15. I use efferdent denture tabs and boiling water. I have four stainless steel double walled thermos containers. Boiling water in, one tablet per container (16-18oz volume), and three for the extra large 48oz. Works on the inside of our stainless steel carafe as well. I prefer not to use abrasives but I will use a dish brush inside if I notice staining inbetween three month cleanings. Doesn’t seem to do anything compared to the denture cleaner.

  16. I had some retainer cleaning tabs handy and tried those. Amazing results after a 3hr soak in hot water from the tap. Less than a minute scrubbing with a bottle brush and it’s sparkling. Coffee stains just flaked off. From what I understand the retainer tabs are a milder formula than denture tabs so I’ll definitely get those next time. Thanks for the tips!

    • Barbara Lowell says:

      Hi … I’m not sure but I think I read that dip-it was a noxious cleaning agent, so doublecheck that. No need to inhale if that is the case. In addition, for me with small storage area tiny house, I need to have products double up for various applications, not another box or bottle in my small bin. Its already overladen with “stuff” that might take years to use up. ;D

  17. Such a helpful and informative article! Thanks Carolyn .

  18. An old restaurant trick for coffee carafes… Throw some pennies in with a little water and swish around (soap optional). Gets the crud off the bottom very well. We use that to get the sludge out of the bottom of jerry cans, too (minus the soap).

  19. miatapaul says:

    I have used dish detergent powder for a long time. Works on lasagna pans, and any pan with cooked on stuff. Even works wonders on grill grates, in a bucket just let soak. Dish powder also works in the bilge but is not very environmentally friendly so use it sparingly, and rinse very well. I have recently started using a bit of Clorox cleaner at work, but you do have to rewash after it soaks for a while. If you can’t find a bottle brush Dollar Store toilet brushes work also, just mark it for kitchen use only!

  20. Any suggestions for cleaning just the pour spout of a thermos? Mine seems clogged because it is pouring slowly; no bottle brush or sponge can reach those tight spots and soaking doesn’t help. I would prefer not to buy a new one as I am quite fond of this one…

    • I use a pipe cleaner for getting into small spaces like bottle spouts, electric chopper parts, and other places where using an old toothbrush won’t reach. I have enough old toothbrushes around to clean several hotels! I have gunk in the bottom of my thermos from using liquid creamer in with my coffee. The thermos is soaking right now with denture tablets.
      I have 2 sets of bottle cleaners, and both big brushes are plenty long but have no bristles on the bottoms. One set came with a pipe cleaner type thing. You can get a set of just pipe cleaners at any tobacco place very cheaply and even reuse them.
      Thanks, all, for the Dip-It reminder and the other tips. I’ve used the ice trick for cleaning carafes for years. Ice is good for sharpening garbage disposal blades, too.

      • FYI:
        The Manufacturer of Dip-it has taken it off the market. I had used it for years on coffee pots and vacuum bottles.

        • Rush,

          Dip-it hasn’t been removed from the market, Some stores no longer carry it; but you can order it from numerous sources,

        • Barbara Lowell says:

          OH THIS IS SO GREAT. I have pipe cleaners in my drawer bugging me because I can’t remember what I bought them for … what a great idea for my juicer cleaning, and other odd areas you can’t get into. I am single and I too have an abundance of toothbrushes, and every time I go to the dentist they give me more!!! Thanks huge!

  21. My word! I just did my first cleaning with 4 denture tablets and water from the hot water dispenser. I let it soak for an hour. You should have seen all the crud that came out. It was rather gross. I had been cleaning the thermos weekly with soap, water, and the bottle brush, and thought it was clean. I noticed a stain in the bottom this past weekend, so I went searching for a solution to get that out. We have a winner.

    It looks like new, now. I think I need to figure out how to clean around and under the plastic seal on the lid. Now that the rest of the inside is shining, I can tell there is a barely perceptible stain around the white seal.

    Thank you all so much.

  22. Barbara Lowell says:

    Don’t forget the Dollar Tree for denture tabs … $1.00 for anything you find there, not like Dollar General and Family Dollar and probably lots of others across the U.S.

  23. FedoraMGTOW says:

    You want to be very careful if you’re cleaning your thermos with vinegar and baking soda. If the solution explodes, it will ruin your thermos. Now my thermos leaks, so I suppose it’s going to the trash. Should have just gone to CVS and bought denture tablets.

  24. I have a stainless steel thermos and had always cleaned it with Crystal dish soap and had no problem. I was always using tea, however this time I used liquid dish soap. The man used coffee with the cream in it and the coffee came out tasting sour. What happened?

    • I would guess that not all the cream got scrubbed out or it wasn’t rinsed thoroughly and there was a bit of soap, which can also give a sour taste — not necessarily a soapy taste.

  25. Judith C says:

    You can get REALLY long handled bottle brushes at home brew stores.

  26. I’ve gotten excellent results with this brush: for US $8.13 at this time. It is a tight squeeze into my small Thermos brand 2 cup bottle but the handle is sturdy and the bristles are squared off and downward pointing for reaching the bottom of the bottle.

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