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  • Writer's pictureCindy Miller

The Basic Definition of Thermal Cooking

Updated: Nov 14, 2020

Let’s Make Sense of Thermal Cooking. Technically, a thermal cooker is a device used to cook with heat. Thermal cooking, cooking with heat. Thermal cookers facilitate retained heat cooking and work like a “slow cooker” cooking food slowly over time. Utilizing retained heat cooking can be as uncomplicated as boiling water and as seemingly complicated as making bread. You will be amazed at how easy it is, armed with a little basic knowledge, to make great meals with retained heat cooking.

Like so many other traditional skills, the art of retained heat cooking has been virtually lost to our society. For most of my life, I had no idea that such a wonderful device as a thermal cooker existed. After discovering the thermal cooker and researching it, imagine my surprise to learn that thermal cooking is not a new concept. In fact, thermal cooking, or retained heat cooking, has been around for hundreds, if not thousands, of years.

What is all the hype about trapping heat to cook your food? The benefits include; energy efficiency, easy to clean, portable, quick and convenient, simple to use, “green”, keeps hot things hot & cold things cold, and traps nutrients and flavor inside. Just to name a few.

The first step in retained heat cooking is to bring food to a boil in a pot. Then place that pot of boiling food inside of an insulated thermal unit. Food continues to cook as the temperature of the food slowly drops over time. The result, when done correctly, is food which will maintain safe serving temperatures for up to eight hours. Thermal cookers can be purchased or assembled using boxes, coolers, blankets, pillows and a heavy pot, making thermal cooking accessible to everyone.

The basics of how thermal cooking works is very simple, the possible variables make it a bit more complicated: quality, temperature, volume, timing efficiency and liquid. The quality of the thermal cooker determines how long the food stays hot inside. Whether using a stainless steel portable thermal cooker or a laundry basket full of blankets, insulation is vital. Air is the enemy in retained heat cooking, both inside the pot and the insulation outside, so pack insulation around the pot nice and tight when making your own. For the cooker to work at maximum efficiency, it needs to be full. The more food in the cooker, the more heat is retained and the longer the food stays hot. Thermal cookers must be 75-80% full and boiling to retain the heat for the full 8 hours. Temperature is key to food safety and convenience. If you own a thermal cooker, own a thermometer. When you know at what temperature your food is going into the thermal unit, you can calculate how long it can stay in the cooker before it needs to be eaten, reheated, or cooled down and put into the refrigerator. Because of the considerable time flexibility in thermal cooking, it is possible to choose when you want to eat the meal. Choose a recipe and preparation method which fits into the general time frame you would like to eat.

I have learned many things while writing the book Let’s Make Sense of Thermal Cooking Cookbook, one which may seem obvious to most, was not to me. I guess I had never thought about it before, but did you know there are 4 basic categories of side dishes? Grains, Legumes, Pasta and Vegetables. With retained heat cooking, two of these categories love this technique and the other two do not. For instance, have you ever boiled pasta and forgotten about it, only to come back later to find your pasta huge, slimy and possibly burnt? Well, it is worse after leaving it for 3 hours or more in the thermal cooker, unfortunately I had to learn that lesson more than once. I would have thought I would have remembered after the first disaster, nope not me, I had to experience it twice. The food was inedible and I threw it away. Needless to say with both pasta and vegetables, sitting in water and heat for an extended period of time is devastating. But, there is no reason to give up hope, with a little education and manipulation of time, both vegetables and pasta can be successfully prepared using this method of cooking. An example for each of these would be to use baggies for precooked pasta and a steamer insert for the vegetables.

Now, let’s take a minute to look at grains and legumes (beans), they are doing a happy dance inside of a thermal cooker. In fact, sitting in a nice hot bath is exactly where they want to be. It is when preparing beans that I see one of the biggest savings of fuel with thermal cooking. For instance, after soaking the beans for at least 6 hours to break down the phytic acid, I put them into a pot of fresh water, add a bit of salt (yes, I know - salt, really? read the book to find out why), and boil for 10 minutes. When was the last time you boiled your beans for only 10 minutes? They do spend the next 5 to 6 hours in the thermal cooker, but at least they are not consuming more fuel. If you are using really old beans it is going to take more creativity to prepare the beans, but so far I have had great success with the 10 minute boil. Prepping beans or grains for a future meal is also a great way to help maximize the efficiency of the thermal cooker. When your plan is to cook less food, only enough for one pot consider precooking a grain for a delicious salad in the second pot.

Up until now we have discussed, bringing the food to a boil when using a thermal cooker. This requires the food to be liquid. Let’s discuss food which cannot be boiled. How can it be prepared in a thermal cooker? Using containers, of course! With container cooking, the options with thermal cooking literally become endless. The process is accomplished by simply putting food, such as bread dough, into a container, covering, and then putting the container into the pot. Next, surround the container with water and bring the water to a boil. After boiling the water for a period of time which is determined by the size of the container, the pot is put into the thermal unit which continues to cook the food, in two hours I have a wonderful loaf of bread. It is possible to use this technique to prepare almost anything, meatloaf, lasagna, shepherd’s pie, even quiche. There are many types of containers which can be used in the thermal cooker. Look for glass, stainless steel and oven bags. I have already thought through possible accessories available for the thermal cooker and have put together a couple of kits which make sense to me, you can find them on my website at under the thermal cooking/kits tab.

The increased variety of food possible to prepare by using containers is great, but there is something I think is even more beneficial. Many people see the thermal cooker only as a preparedness item to be used in times of emergency, mostly because it is seen as something which will feed a lot of people. Many of the people I talk to have small families and the thermal cooker makes too much food for them to utilize on a regular basis. With containers, it is now possible to prepare the amount of food needed in containers without having to worry about eating leftovers for several days.

As if what I have mentioned so far is not enough, I would really like to get your creative juices flowing. So far everything seems relatively logical. Now let me go over a couple of meals which can be prepared in the thermal cooker which are a bit more creative. Let’s say I would like to make soup in the thermal cooker, something with a broth base, like onion soup. I also would like bread to go with the onion soup. I fill half pint wide-mouth mason jars 1/3 full of bread dough, cover with the lid and ring and place down into the soup. When the soup cooks, so will the bread. Remember, put the mason jars into the soup when adding the liquid, not to the boiling soup. Mason jars will break when they are cold and the water is hot, yes I learned that from experience also.

Next, let’s prepare a whole meal in the thermal cooker. Place 5-6 small to medium potatoes into the bottom of the 7 L pot. In an oven bag place 1 ½ # - 2 # chicken tenders or ribs and add your favorite seasoning or BBQ sauce. Now comes the fun part, mix the meat and seasoning together from the outside of the bag by mushing the bag until the sauce is covering the meat. Flatten out the bag as much as possible and lay it over the potatoes in the pot. Add water to cover the meat and bring to a boil. Boil for 10 minutes. In the upper pot prepare another dish baked beans, green beans or corn are good options. Place the top boiling pot of vegetables over the bottom boiling pot of meat and potatoes and place into the thermal unit. Leave for at least 2 hours. Just before eating add ultra jel or some other instant thickener to the oven bag of meat, gravy for the liquid around the meat will thicken in about 5 minutes. There you are, a full meal; meat, potatoes, gravy, and vegetables all in one pot, to eat wherever and whenever you would like.

As you can see, a thermal cooker is ideally suited for the needs of practically everyone. For a busy family, an elderly couple, or a young business professional, the thermal cooker works great. In all cases, simply using the thermal cooker creates savings in time, economics, nutrition and the environment. The options are endless and rewarding. For more information or to watch a video on thermal cooking visit


Facebook page - Let's Make Sense of Thermal Cooking Cookbook

YouTube Channel - Let's Make Sense of Thermal Cooking Cookbook


Thermal cookers are like a big crock pot, cooking food slowly over time. While slow cookers require constant electricity, thermal cooker utilizes heated (boiling) food to complete the cooking process.

Purchase Retained Heat Containers, Cookbooks and More here!

Learn to make your own HopeSac for thermal cooking: https://thermalcooking.vipmembervault...

OTHER VIDEOS YOU MAY LIKE: Ideas to Use your Thermal Cooker for a Whole Week:

Join us HERE for the Thermal Cooking Online Course!!! https://thermalcooking.vipmembervault...

Live Digital Cookbook: https://thermalcooking.vipmembervault...




DISCLAIMER: Links included in this description might be affiliate links. If you purchase a product or service with the links that I provide I may receive a small commission. There is no additional charge to you! Thank you for supporting The HopeSaC Project so we can continue to provide service to those in need!

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