A Homemade Thermos Cooker, by M.P.

A thermos cooker is an energy saving cooking device. Earlier versions were a vacuum thermos that you placed uncooked food and boiling water into and then sealed it up, and in a few hours you had cooked food. Later versions have a pot that you put your ingredients into and place on your stove; you then bring the contents to a boil and place the pot into an insulated outer pot to hold the heat in and cook the food. Thermos cookers do not speed up cooking times; they only save energy, and in fact cooking times can be significantly longer than other methods. To cook food in the shortest amount of time, use a pressure cooker. Any serious prepper should already have and use a pressure cooker. The theory behind the thermos cooker is to limit the amount of heat that escapes from the cooker and hold that heat inside for a long period of time, therefore cooking the food inside with very little energy expended. Depending on the amount of food and liquid that is inside, a thermos cooker can also keep food warm for a very long time. Thermos cookers can be purchased at many online stores, such as Amazon. I liked the concept of the original thermos cookers but was disappointed with the size limitation, since it could only cook small to medium quantities. Current versions of the thermos cookers are available in sizes up to eight quarts or so, but they are quite expensive. I did some thinking and came up with an alternative that suits my needs very well and cost considerably less. I created my own thermos cooker using an 8-quart pressure cooker, three cardboard boxes that nest together, some foil-lined bubble wrap, and some contact cement. Two cardboard boxes would probably be sufficient, but according to my IR thermometer, with three boxes, the outside temperature is only a few degrees above room temperature. The pressure cooker that I have is an 8-quart Presto model 01370, which has small handles on opposite sides at the top. This style works much better than smaller pressure cookers that have one long handle coming off the side of the pot due to the large amount of space below the handle that has to be heated, thus wasting heat. Pressure cookers can be purchased at most stores that carry cookware and many online stores, such as Amazon. The pressure cooker that I use measures 10 inches in diameter not counting the handles, 15 inches in diameter with the handles, and is 9 inches tall with the lid locked.

Making Your Thermos Cooker

The inner box measures 12 inches wide, 15 inches long, 10 inches tall, and 20 inches diagonally. The pressure cooker fits in diagonally with a little room to spare. The middle box measures 12.75 inches wide, 18 inches long, and 11.75 inches tall. The outer box measures 17 inches wide, 20.5 inches long and 15 inches tall.

Boxes can be scrounged from stores or bought at one-stop stores, such as Wal-Mart, big box hardware stores, as well as moving and storage facilities. Foil lined bubble wrap can be found at any big box hardware store in the insulation isle. Spray contact cement can be found at any big box hardware store in the adhesive isle.

Inner Box

First, I cut the top flaps off of the inner box. I then cut one piece of bubble wrap to fit in the bottom of the inner box and I glued it in with contact cement. Next, I cut one piece of bubble wrap for each of the inside walls of the inner box and glued them in. Next, I cut bubble wrap for each of the outside walls and the bottom of the inner box and glued them on. The inner box now fit loosely inside the middle box. I centered the inner box inside the middle box and filled the gaps with bubble wrap; these don’t need to be glued. Finally, I cut a piece of scrap cardboard to the size of the opening of the inner box and cut and glued one piece of bubble wrap to it. This is used as a lid to seal up the inner box, once the cooker is inside.

Middle Box

First, I cut the top flaps off of the middle box. I then cut and glued bubble wrap on the outside sides and bottom of the middle box, just like the outside of the inner box. The middle box now fit inside the outer box with some room to spare. I centered the middle box inside the outer box and filled the gaps with bubble wrap. (These don’t need to be glued.) Next, I cut a piece of scrap cardboard to the size of the opening of the middle box and cut and glued two pieces of bubble wrap to it. This is used as a lid to seal up the middle box once the cooker is inside.

Outer Box

First, I cut the top flaps off of the outer box. Next I cut a piece of scrap cardboard to the size of the opening of the outer box and cut and glued two pieces of bubble wrap to it. This is used as a lid to seal up the outer box once the cooker is inside.

Thermos Cooker Operation

You will find some sample recipes at the end of this article. Place the food to be cooked along with any spices and cooking liquid into the pressure cooker and lock the lid in place. Bring the pressure cooker up to high pressure under medium-high heat. As soon and the cooker is up to high pressure, cover the steam vent with a hot pad or small kitchen towel to prevent steam burns. Place the pressure cooker into the inner box, carefully remove the hot pad from the vent, and put all of the lids in place. Start the cook timer.

There are two notes to pay attention to:

  1. Depending on the amount of ingredients and the cooking time, the pressure cooker may be very hot even after setting for many hours. Once the time has elapsed, open the boxes and using hot pads remove the cooker. If the pressure cooker still has pressure, release the pressure using the method called for in the recipe.
  2. If the volume of food and liquid is increased, the additional thermal mass will require that the cooking time be shortened or the food will be overcooked. If the volume of food and liquid is decreased, the reduced thermal mass will require the cooking time be lengthened or the food will be undercooked. Reducing the thermal mass significantly will at some point, cause there to not be enough heat stored to cook the food.

The thermos cooker works best using either electric or gas stoves because of the constant heat provided. Wood stoves can be used, but cooking times will vary due to temperature variations, which will lengthen the time to get to high pressure, which in turn will probably shorten the cooking time.

Recipes

These recipes are based on an elevation of 4,000 feet. The cooking times of the recipes may need to be adjusted slightly based on your elevation and the desired doneness of the food. Higher elevations require longer cooking times because the boiling point of water decreases 1.8 degrees F for every 1000 feet increase in elevation above sea level.

White Rice

Total time about 45 minutes – Makes about 6 cups

Note: white rice cooks so fast that a thermos cooker is not required.

Ingredients:

  • 3 cups long grain white rice
  • 3 1/2 cups cold water
  • 2 1/4 tsp salt or other seasonings

Instructions:

  1. Place rice, water, and seasonings into the pressure cooker; bring up to pressure under medium-high heat.
  2. Remove from heat and place on a trivet or hot pad.
  3. Cook 30 minutes. When the time is up, if there is any pressure left, drop the pressure using the quick release method. Crack the lid and let stand for a few minutes.

Brown Rice

Total time: 1:30 – Makes about 6 cups

Ingredients:

  • 3 cups long grain brown rice or rice blend
  • 5 1/2 cups cold water
  • 2 1/4 tsp salt or other seasonings

Instructions:

  1. Place rice, water, and seasonings into the pressure cooker.
  2. Bring up to pressure under medium-high heat; place a cloth over the relief valve and immediately place into the insulated box.
  3. Close up the box; cook 1:15.
  4. Remove from the insulated box; if there is any pressure left, drop the pressure using the quick release method.
  5. Immediately remove the pressure cooker lid. Leave the lid cracked if not serving immediately.

Beans

Total time: 1 hour – Makes about 10 cups

Ingredients:

  • 4 cups dry beans, soaked 8-24 hours
  • Water

Instructions:

  1. Place beans into the pressure cooker; add enough water to cover the top of the beans by 1”.
  2. Bring up to pressure under medium high heat; place a cloth over the relief valve and immediately place into the insulated box.
  3. Close up the box; cook 18 minutes.
  4. Remove from the insulated box. Let the pressure drop naturally. Drain any excess liquid if desired.

Chicken Stock

Total time: about 2 hours – Makes 3-4 quarts

This recipe can be used without the vegetables and seasonings to cook a chicken for shredding.

Ingredients:

  • 1 whole chicken rinsed, giblets discarded, excess fat removed
  • 2 carrots, cut in large chunks
  • 3 celery stalks, cut in large chunks
  • 1 large onion, quartered
  • 1 head of garlic, halved horizontally
  • 1 turnip, quartered
  • 1/4 bunch fresh thyme or 1 tsp dried thyme
  • 2 bay leaves
  • 1 teaspoon whole black peppercorns
  • Water

Instructions:

  1. Place all ingredients in the pressure cooker; Add enough cold water to just come to the top of the chicken and vegetables. (Too much will make the broth taste weak.)
  2. Bring up to pressure under high heat; Place a cloth over the relief valve and immediately place into the insulated box.
  3. Close up the box; cook for 1:30.
  4. Remove from the insulated box; let the pressure drop naturally.
  5. Carefully remove the chicken to a cutting board.
  6. When it’s cool enough to handle, discard the skin and bones and shred the meat.
  7. Carefully strain the stock through a fine sieve into another pot to remove the vegetables.

Pork Roast For Shredding

Total time: about 2:25.

Ingredients:

  • 3 pounds of pork loin, pork roast, or pork sirloin, cut into 2 to 3-inch chunks
  • 2 cups cold water
  • salt, pepper or any other desired spices

Instructions:

  1. Put the trivet or basket in the bottom of the pressure cooker.
  2. Add the pork, water, and spices; put the lid on the pressure cooker and bring up to pressure under medium-high heat.
  3. Reduce heat and cook for 20 minutes, maintaining high pressure. Place a cloth over the relief valve and immediately place into the insulated box. Close up the box; cook for 2 hours.
  4. Remove from the insulated box, letting the pressure drop naturally.
  5. Remove pork to a cutting board and allow it to cool until it is cool enough to handle. Shred the pork while warm.
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One Response to A Homemade Thermos Cooker, by M.P.

  1. Michelle from canada says:

    Hello James, and Hugh

    Thank you James, for this text on these special cooking devices. These are ingenious
    invention. I am already shopping. I am reading everything you and Hugh are posting about being prepared and equipment, country living.

    You two probably don’t realise it is hard to do this transition for most people.. But it is. I am talking about relocation. I am considering relocation in my country. But even basic prepping is hard for most people because they have been conditioned to gravitate around the shopping mall. It is a new way of thinking for them. I don’t have that problem. For me relocating is the big one. I will keep talking to both of you James and Hugh.
    This blog is a good support for all the people who are trying to follow in your foot steps.

    I did a print out of the information you found on thermal cooker . I like it that much.

    And Hugh , you are doing a lot of work on this blog. Thank you.

    Michelle from Canada

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