Here are the basic steps for cooking food with a thermos:

Purchase a Quality Thermos

Your plastic Hello Kitty lunch thermos will not enough, I’m sorry to say. You need a quality metal thermos in order to retain enough heat to cook food. That doesn’t mean that a thermos will be expensive however. I use a quart size stainless steel Thermos brand thermos I bought at Walmart for around $25. It works great.

Pre-Heat Your Thermos

Before you start putting food into your thermos you need to preheat it with boiling water. This will heat up the metal in the thermos before you put your food in. This way, the water you put in with your food won’t be cooled down by having to heat up the thermos first (First Law of Thermodynamics, I think).

I like an electric kettle for quickly boiling water for this kind of work. It will boil water faster, safer, and easier than using your stove or the microwave.

Measure and Boil More Water

Most recipes will require boiling water to be added to the food for cooking. As soon as you start pre-heating the thermos, measure and start boiling the next amount of water that will be added to the food.

Prepare Food

While your water is set to boil start gathering the food you’re going to cook. Measure the grains or other ingredients and have them ready to dump into the thermos.

Combine and Wait

You don’t have to get crazy, but you want to empty the hot water out of the thermos, put your ingredients in, and then pour the boiling water in as quickly as you can. I use a canning funnel to help pour the ingredients into the thermos. You might even need a more narrow funnel if your thermos has a narrow opening.

Once you’ve poured all your ingredients into the thermos, close it up (don’t screw it down so tight it’s hard to open later), give it a nice shake to combine, and lay it down on its side on a counter.

Why not stand it up, you ask?

Well, you want the ingredients to stay in contact with the hot water as evenly as possible. If you stand the thermos up, the heavier food will sink to the bottom and will not cook as evenly.

For backpackers and campers:

When I’m out on the trail I try to insulate the thermos as best I can overnight. I either wrap it in some clothes or a jacket or I’ve even put it in my sleeping bag on colder nights.

When Is It Done?

It depends…

Oat groats take a lot longer to cook than steel cut oats. Wheat berries take longer to cook than cracked wheat.

The nice thing about thermos cooking is you can often tell if the food is done by the way it sounds when you give the thermos a shake. A few examples:

  • Quinoa – when you first put in the quinoa, salt, and water, it will slosh all around when you shake the thermos. In time it will thicken and then near the end it will barely move at all. When it barely moves it’s done!
  • Oats –  will slowly thicken during cooking and you can tell when they’re ready based on sound. They won’t ever thicken like the quinoa (not if you add the right amount of water!), but you’ll quickly learn when they’re done.

Don’t worry. You can always open up the thermos and take a look and we also give suggested cooking times. The nice thing about a thermos is that it’s very difficult to overcook anything and taking a quick peek once or twice isn’t going to release enough heat to cause a problem.


Once your food is done you can pour (or spoon) some onto your plate and then just leave the thermos with the rest of the food on the counter. It’ll sit there at the perfect temperature for hours! So you could prepare some oatmeal to enjoy early in the morning and then leave it on the counter for your kids or spouse to eat once they’re ready for breakfast.

It’s the perfect way to fix fast food that’s actually good for you.

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