“Hay boxes,” thermal cookers, or retained heat cookers have been around just about forever. Legend has it this was used by the early pioneers as well as during WWII to help make the most of limited fuel. It is still used regularly in many developing countries.
The food is brought to a good strong boil in the morning and then placed in an insulated box to continue simmering all day. The basic principle is to insulate the pot well against outside temperatures in order to retain the heat in the pot. Regardless of your choice of insulation, make sure you have at least 4 inches on each side. It takes about 4 times as long to cook, but uses significantly less fuel.
Good candidates for cooking in a thermal cooker include soups, stews, chili, beans, rice, wheat berries, or other items which contain a lot of liquid. Large pieces of meat will not work well.
Always make sure that the food stays above 140 degrees. Bacteria will thrive in a warm environment, but can’t survive high temperatures. If the food is below 140 degrees when you open the cooker, it may be dangerous to consume. Bring it back up to a strong boil before eating. It is better to throw food away than to risk making your family sick.
This method absolutely works! If a problem occurs, evaluate your cooking technique. Do you have enough insulation? Was the food brought up to a strong boil? Were the pieces of food too large? Did the food completely fill the cooking pot? Experiment while food is cheap and available.
Understanding how cook using retained heat is a great skill to master. Cindy Miller has written a great book Let’s Make Sense of Thermal Cooking Cookbook: Yesterday’s Methods Using Today’s Tools that you might want to check out.
Ice Chest Method – Line an ice chest with towels or blankets. Place the hot pot on the towels/blankets and cover with additional fabric. Do not allow the hot pot to touch the sides of the chest.
After many uses our ice chest began to come apart at the seams due to the heat. However, it works really well and is easy to move and transport. Tuck the pot in and cover with the blankets, making sure that all sides are well-insulated. Close the lid and forget about it.
Wonder Box – This homemade thermal cooker is made from soft 
cotton or broadcloth (any washable cloth will work) and filled with Polystyrene beads (dried corn husks, feathers, scrap nylon materials, sawdust, wood shavings, straw, hay, dry grasses or any other non-toxic insulating material may be used). The hot pot is set in the bottom of the insulated fabric box and cover with the attached insulated fabric lid.
It is important to use materials which are washable because after a while the bag will start to stink. If using materials such as hay or wood shavings you may develop mold inside the insulating material over time and will need to replace the insulation. Make sure you allow the bag to dry and air out well.
The photo above is a Wonder Box which is stuffed with Polystryrene beads that can be thrown in the washer to clean. The pot fits snugly into the bottom pillow and the smaller pillow fits over the top. It works amazingly well.
Cardboard Hay Box– We made this as an experiment and loved it. It did a fantastic job of holding temperature. Once we put the boiling pot of beans in this box in the early morning and 12 hours later it was still piping hot. Have fun and experiment!
There are a hundred different ways to make a hay box. The high moisture content made this one stink and we ended up throwing it away after a few years because it could not be cleaned.
Be creative and use whatever resources you have. One woman told me that as a child her mother would line the bathtub with blankets, put the hot pot on top, and cover it with more blankets. Just make sure that you have at least 4″ of insulation on all sides. The more the better.
Don’t be tempted to open your retained heat cooker to check on the food as you will lose too much heat. My experience has been that the food is piping hot when I take it out 8 hours later. If for some reason yours is not, bring it back up to a boil before serving.
Modern Thermal Cookers – I absolutely love this Thermos thermal cooker! It works like a hay box using modern technology which makes it super simple to use. You bring your dinner up to a boil in the pot, put it in the carrier, and it continues to cook using no additional energy. I put mine back into the pantry and let it work it’s magic or pack it with us on family outings.
The manufacturer guarantees heat or cold retention for 6-8 hours. I found that it just did not perform quite as well as the more primitive methods. I love the convenience, so I increase the insulation by wrapping it in a towel or baby blanket. The thermal cooker is wonderful for soups, chili, beans, and stews. I use it to keep potato or fruit salads cold. You just won’t believe how incredible thermal cooking is until you try it.
The concept of commercial thermal cookers has taken off and there are several other brands available now. Tamaya offers a 7 quart thermal cooker, my sister-in-law loves her Saratoga Jacks thermal cooker and Tiger makes high quality thermal cookers in several different sizes.
The various sizes are a great benefit because you need to completely fill the pot for optimal performance. A small thermal cooker will work when feeding just a few people, while you may need a larger one when you are cooking for a crowd.
When investing in a commercial thermal cooker, be sure that you buy quality and it will be a valuable tool that you will use for many years to come.
Retained heat, or thermal cooking, is a convenient way to conserve energy every day, but it may be a life saver when fuel is limited during a crisis. I challenge you to experiment with retained heat cooking and discover what a wonderful tool it can be.
Thanks for being part of the solution!
