How long is it safe to keep food hot in a thermos

Are you wondering how long is it safe to keep food hot in a thermos? Don’t worry, you are not alone.

how to keep food hot in a thermos safely for school lunches or office lunches via

I mean, you heat it up in the morning… and the food is cold by lunch! How does that happen!?

Each week, I receive dozens of emails from MOMables subscribers wondering the same thing.

Since the invention of a thermos, people want to know how long will the food last hot, how long should the food be heated, and of course if it’s safe to eat.

Is your child’s lunch going to make him or her sick? Probably not, so relax a little. Most common food poisonings result from eating foods that contain large numbers of harmful bacteria.

The likelihood of the lunch you pack for your child in the morning growing serious amounts of bacteria in 4-5 hours, when packed properly in a lunchbox, inside an insulated lunch bag and with an ice-pack is slim (but sure, it could happen).

Today, we are talking hot foods. Hot foods you want to pack for lunch in a thermos.

After a lot of testing in the kitchen and purchasing different thermos containers I believe I have a pretty good guide for you to follow.

How long is it safe to eat? It depends on the container and how you heat up the food.

  • Bacteria grows quicker between 40-140degrees F. Perishable foods should not stay at that temperature range longer than 3 hours.
  • Food packed inside any lunch container should be cooked throughly at a safe temperature (no raw eggs, avoid  raw onions, undercooked meats or fish).
  • Soups, pastas, and any other hot foods should be heated on a stove to a boiling point (212F, 100C) and microwaved piping hot prior to packing.
  • Thermoses must be preheated prior to filling.

The problem is that most parents heat up foods as hot as they would normally serve it for dinner. Remember, you are not heating up the food to eat now, you are heating it so that it can be safely eaten 3-5hours later. When you heat food like this the  lunch will be cold, regardless of the container you use. 

I purchased my containers on Amazon – all listed in the MOMables store- although most are available at many stores near you.

I tested the thermos containers three times by preheating the thermoses before adding the food each time. Food was filled at 7:30am and the lid came off at noon.

Here are the 5 results.

  1. Thermos Brand 10oz capacity Funtainer stainless. The temperature of the soup began at 210 degrees F and after 4.5 hours it was 138. Would I recommend this container? Yes.  It’s great for younger kids, easy to open and fits a good portion of food.
  2. Thermos Brand 10oz capacity Foogo stainless. This one is similar to the Funtainer. Temperature began at 208 degrees F and after 4.5 hours was 134. Would I recommend this container? Yes. I own one. Like the one above, it’s great for younger kids.
  3. Aladdin 12oz BPA-free plastic. The temperature began at 210 degrees and after 4.5 hours it was 110. Would I recommend it? yes and no. Yes, if you are an adult and have access to a microwave and can reheat the food. It’s difficult for younger kids to open since the lid is wide (my 7yo could not open it).
  4. Lunchbots 16oz capacity stainless container. The temperature began at 210 degrees F and after 4.5 hours it was 130. Would I recommend? Yes. I own one. It has a wider mouth so it can be difficult for the younger ones to open. It has a larger capacity so it’s perfect for bigger appetites.
  5. Stanley 17oz stainless. The temperature began at 210 degrees F and after 4.5 hours it was 165 degrees! It was nearly too hot to eat. Would I recommend? Yes. I bought it for this test and will be using it for my husband’s lunches since he typically leaves at 7am and doesn’t eat until 1 or 2pm sometimes. It’s a great option for older kids with bigger appetites. It wasn’t difficult to open since the mouth isn’t as wide as #3 and #4. The only con is that it is bigger and bulkier.

To prove the test, I heated up a bowl of soup to a temperature my kids would eat 150 degrees (and even this was a bit hot for my son). I filled the thermos with the hot soup and after 4.5 hours in containers 1-4 was cold (barely warm at best) and in #5, the Stanley it was warm and edible.

My advice is for you to make sure you preheat your thermos, heat up the food to a boiling point or piping hot and purchase a thermos that suits your needs. 

Ask yourself: will the thermos fit in my child’s lunchbox? how much food will I filling it with? will my kindergardener be able to open it? Remember, that with any new container you purchase for your child, you must teach him/her how to use it first at home.  

If you are pretty new at lunch packing, need school lunch ideas, or need a little direction to make sure your child eats a varied diet, you are not alone. You can always subscribe to our school lunch plan for $6 per month.

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  1. Rebecca says


    I struggle with keeping foods (other than soup) above 140 degrees from 7:15am to 12:15pm which is the time between when my sons lunch is packed and eaten. Any further advice? I’ve reheated spaghetti and marinara on the stove. I can only heat it to about a maximum of 180 degrees without burning it before putting it in a thermos preheated with boiling water. I’ve tested the temperature and after 2 hours using the funtainer thermos you recommended and it is in the neighborhood of 130 degrees which concerns me because for the remaining 3 hours it would be in the danger zone. I’m still so puzzled as to how to tackle a safe hot lunch. Thanks so much for your thoughts.

    • says

      Rebecca, the foods we tested in our tests were heated in a microwave (sorry!) stirring often to prevent hot spots. As a mother of 3, I am less concerned with “safe temperature issues” in winter than summer. My biggest concern is where my kids’ hands have been (school bathroom… gross) rather than food that I’ve prepared at home and cooked it thoroughly the first time. Of course, you have to do what’s best for your family and I am glad you are testing this for your own precautions.

      • Rebecca says

        Thanks so much for your additional thoughts on keeping hot lunches hot and safe Laura. I too am most concerned about clean hands at lunch time. I actually pack a mini alcohol based hand sanitizer in my son’s lunch !

  2. Connie says

    To keep lunches hot I heat food really hot, like said above. I also put boiling water in the canister to heat the container. And remove it, just before adding the food. That’s way your food doesn’t start cooling down right away from putting the food into a cold canister.

  3. says

    I just want to say Thank You for your suggestion about keeping my child’s food hot in a thermos. I wouldn’t have thought about it. My son is so happy that he can have other foods besides PB & J or bagels.
    Thank you again. Can’t wait to see what other ideas you have.

  4. Rosa says

    Do you know of any rectangular container that can keep food warm? Something that the kids can open up and eat in like a small plate? I currently use a Thermos too but the mouth of the container is small. Short of using 2 Thermoses, is there one that can keep 2 different foods warm while keeping them separate? My son does not like the sauce or meats mixed with the pasta or rice.

  5. C says

    Do you keep foods besides soups warm? Weird question but my daughter loves sauteed shrimp and asked if I could pack her some in her stainless thermos. Do you think it would remain warm and safe even though it won’t be completely full? My husband is convinced that this is a horrible idea.

    • says

      I use a thermos more often for other leftovers than just soup! A thermos is a wonderful idea. If your food was cooked to a safe temperature for dinner, reheating it and placing it in a thermos will be no problem.

    • Laurie says

      Hey, C! Since shrimp take almost no time at all to cook completely, I’d recommend actually starting with raw shrimp in the morning. It might take an extra minute or two in the morning, but if you’ve prepped them for dinner, then they’re ready to cook.

      Just make sure to hold boiling water in the thermos until ready to place the freshly cooked shrimp into it. I’ve done this myself for shrimp and seafood dishes, and haven’t had a cold. or otherwise unappetizing dish yet.

  6. Anna says

    What if my child’s lunch time isn’t until 6-7 hours after? I leave for work in the morning at 6:15 AM, dropping him off at the extended hours program. (He eats breakfast there). Lunch isn’t until after noon.

  7. Erica munden says

    I would like to know if any one has any suggestions on a food box or something to keep food hot, I,m going to do a food service driving round before I buy a jiffy van,

      • Kelly says

        The catering company my daughter worked for used regular coolers like igloo. They heated the food in foil serving dishes and stacked them in the coolers.

  8. Ann Marie says

    This may be a silly question, but his do you heat up the thermos? Is it microwave safe? The one I own has a metal interior.


  9. Nikki says

    I am looking for a good container for my husband that will hold plenty of food for him and keep it warm for quite a while. I was checking out the Stanley you shared about above and while reading reviews some people was saying that this was great at first and then lost its seal and wasn’t keeping the food hot for long, after only a month or so. I was wondering if you have experienced this at all? Thanks soo much, just found your site today (from 100 days of real food) and already love it!

    • says

      Hi Nikki! Thanks for visiting us! I love that Stanley thermos. That’s the one my husband takes to work. The seal might of come off for other people if they wash and dry the lid in the dishwasher. I only wash the bottom of it, the top by hand. The “seal” is a rubber gasket/band and can come loose with high temperatures. I’ve had mine for over a year with 2-3x week use and no issues. :)

  10. Amie says

    You have mentioned heating up the thermos but most are stainless steel so can’t go in the microwave. How do you recommend heating them up properly?

  11. Kimberly says

    Thank you for this informative post! I love your site, and your newsletters. It is nice to follow you on Pinterest, as well, to see specific articles like this one on mornings when it seems like I need the advice the most! Your efforts for this experiment will help many, many Moms out there to pack great hot lunches! I do have one question – when I pack a Thermos with hot lunch for my kids I often don’t know what else to include with the entree. I am so used to packing items with a cold pack that I don’t know what accoutrements I can send with a hot Thermos full of, for example, ravioli with sauce. What items do you suggest?

        • MaryB says

          I use a Packit for my kid’s lunches and we put the Thermos inside with the rest of the food. The food inside the Thermos stays hot just fine. We use the Funtainers.

  12. Debbie W says

    Excellent advice. I have the 10 oz. Thermos brand stainless containers plus another bigger stainless container that I don’t remember the name of. I always preheated the container by pouring boiling water in it. After dumping the hot water, I then added the hot soup. My daughter had no problems at all when she was young with this. Especially since she’s my soup kid. From when she was tiny to today, at 21, she will still eat soup before most other things.

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