Thermoses allow us to switch things up and enjoy a nice hot lunch, whether it’s your favorite leftovers or homemade soup or even keep items like smoothies or yogurt parfaits chilled!
The questions “how long is it safe to keep my food hot in a thermos?” and “how long will food last in a thermos?”, or “what thermos containers are best?” are notable concerns for many parents packing school lunches.
Properly packing hot and cold food into a thermos container is essential in ensuring that your food will be safe to eat by the time lunch rolls around so let’s go over both methods. Since packing cold foods is super simple, we’ll start there.
When it comes to packing milk, smoothies, or a yogurt parfait as long as the food does not sit at a temperature above 40F you are good to go. Before packing cold food, you do need to chill the thermos, which can is done by placing the thermos container in the freezer overnight, once your food is packed and sealed place it in the lunch bag along with a freezer pack. Ta-da!
Now onto the hot meals! Ever heated your food in the morning, packed it in a thermos and by lunch it’s was cold? Yup, me too but before you throw away that thermos container watch the video below to see if you are correctly packing hot lunches.
As you saw in the video, before packing hot food into a thermos, it needs to be HOT! Remember that hot lunch we talked about earlier? Yes that one, well it’s likely that your food wasn’t properly heated before being packed into the thermos. The good news is that there is nothing wrong with your thermos, hoorah!
How long can food last in a thermos and still be safe to eat?
Given that you cooked the food to a safe temperature and then warmed it up to a piping hot temperature, the food inside the thermos container is not likely to go bad.
But because I love you guys, I’ve researched proper food preparation and storage so that you can safely pack hot lunches for your family! Here’s what I’ve learned:
- Bacteria grows quicker between 40F and 140F, so perishable foods should NOT stay at that temperature range longer than 3 hours (therefore, hot foods should be heated to 212F a.k.a “too hot to handle” before packing in a thermos).
- Thermoses must be preheated before filling. This step often skipped, but it’s easy to do and worth it on cold winter ways when you want to pack leftover homemade Mac and Cheese or Chicken Alfredo.
How to Warm a Thermos
If your food isn’t keeping warm as long as you thought, you need to pre-heat your thermos container. Here’s how:
1. Boil water
2. Fill thermos container with boiled water, cover.
3. Wait 5 minutes and warm food in the microwave while waiting.
4. Empty the thermos
5. Place piping hot food into thermos, close.
6. Pack and enjoy!
Food packed inside any lunch container should be thoroughly cooked through, so no raw eggs, onions or undercooked meats or raw fish.
How to Keep Food Cold in a Thermos
Now that we know what to do with our thermos soups, pastas and leftovers, the question remains – how can you keep food cold in a thermos? If you are packing smoothies or yogurt, you’ll want to make sure those things stay chilled to temperature as well. Here’s how to make sure your cold food stays cold in a thermos lunch.
1. Place thermos in the fridge with some ice water inside it to chill
2. After thermos has chilled, put your smoothie, drink or other cold food items into the thermos and pack it in the lunchbox
3. Place the thermos near an ice pack in the lunchbox to make sure it stays nice and fresh until lunchtime.
How to Pack Hot and Cold Items in the Same Lunchbox
One question I get asked all the time, is if hot and cold items can be packed in the same lunchbox. The answer is, absolutely they can! This is one reason I love using large, square lunchboxes, it helps make sure I can get everything my kids need for lunch, in one simple carrying case.
Watch how easy it is to pack hot and cold lunch items together in the same box:
Now for the thermos testing.
Below are my four thermos container recommendations. Each container was tested three times with the same method: Heating soup to 210F, packing it into the thermos and waiting 5 hours before checking the soup’s temperature. The results:
Great for kids, easy to open and fits a good portion of food – 1 ½ cups! The temperature of the soup was 210F when placed into the thermos, and after 5 hours, it was 138F –perfectly warm and good enough to eat.
Buy the Thermos Funtainer here.
Similar to the Funtainer (with the exception of a rubberized grip) and great for kids. Totally worth purchasing! The temperature of the soup was 210F when placed into the thermos, and after 5 hours, it was 134F.
Buy the Thermos Foogo here.
I love and own this one merely for the size. It has a wide opening which makes it more like a bowl and easier to eat out of. However, it can be a little more difficult for younger kids to open because of the wide lid. It also holds a lot of food, 2 cups!
The temperature of the soup was 210F when placed into the thermos, and after 5 hours, it was 130F.
Buy the Lunchbots Food Jar here.
This one WORKS! The temperature of the soup was 210F when placed into the thermos, and after 5 hours, it was 165F!
It was almost too hot to eat, but after a few minutes of being open, the soup was perfect! It’s also great for both kids and adults, easy to open and since it’s 17 ounces that means more room for food, about 2 cups.
Buy the Stanley Insulated Jar here.
You can’t go wrong with any of the options above for packing lunches. A thermos is a terrific vessel for repurposing leftovers and sending hot and cold foods for lunch!
If you need ideas to fill the thermos containers, check out our meal plans. Our real food dinners can yield leftovers, and our lunches will add variety to any lunchbox, guaranteed.
Plus, you get a shopping list, a meal-prep sheet with a breakdown of what to prep when… it’s practically a kitchen assistant at pennies per day. Want to try it out first before you commit? Get a free week of our meal plans here!
One thing to consider prior to sending food in a thermos for the first time is to let your child try it at home first, so they are comfortable opening and closing the container own their own. A great place to start is with these delicious thermos soup recipes.
What are some of your favorite things to pack inside a thermos?