“Hay boxes,” or thermal 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. Regardless of your choice of insulation, make sure you have at least 4 inches on each side. It takes about four 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 cooker. Do you have enough insulation? Was the food brought up to a strong boil? Were the pieces of food too large? Experiment while food is cheap and available. Understanding how to use thermal cooking is a great skill.
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 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 will do). 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 awhile it will start to stink. If using materials such as hay or wood shavings you may develop mold inside the insulating material over time. Make sure you allow the bag to dry and air out well. The photo to the left is of a version made stuffed with Polystryrene beads that can be thrown in the washer to clean.
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 it and 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 8-12 hours later. If for some reason yours is not, bring it back up to a boil before serving.
Modern Hay Box – I absolutely love this! 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 just throw a towel or blanket over it to increase insulation when I know it will be a long time before we plan to eat. It has TherMax double wall vacuum insulation for maximum temperature retention. Unbreakable stainless steel interior and exterior. This is wonderful for soups, chili, beans, and stews. You just won’t believe how incredible thermal cooking is until you try it.