Retained heat cooking is a very old fuel saving cooking method that dates back to medieval times.

You’ll find reference to this type of slow cooking in many vintage cook books. This technique was commonly used by farmers while working the fields. They would simply nestle a pot inside a hay bale to keep it warm. Some households has special wooden boxes designed especially for this method of cooking.

The process is similar to that of a modern slow cooker. You start cooking your food in a pot, then you transfer the pot to an insulated box for long, slow cooking. Its a great way to reduce your energy consumption & save money and works well when you are worried about fuel conservation/emergency cooking during power outages.

Wartime Farm

My desire to try this came from watching wartime farm (episode 2) where Ruth cooked a stew using a hay box. You can watch the scene here - skip to 27:00 if you want to get right to the cooker.

Do It Yourself Retained Heat Cookers

Here is a selection of retained heat / hay-box inspired cookers for you to browse through.

Hay Box

With a sturdy box, crate or basket and some fine straw, hay or wool, you can quickly make a hay box cooker. Choose an insulating material such as hay, straw or wool to pack the box with. You can stuff a pillowcase with material for the top and then cover the whole thing with a heavy lid. You can find a tutorial on making a hay box cooker here.

DIY Wonderbag

If you’ve got sewing skills you can make your own wonderbag style of retained heat cooker. This is a fabric bag (sort of like a bean bag, that you nestle your pot into. You can find detailed instructions to make one here!

Cooler with Sleeping Bags

This is a really easy and economical way to try thermal cooking since most of us have an insulated cooler and sleeping bag kicking around in our garage or storage shed. Here is one great example

Plastic Storage Tote with Insulated Cushions

Here’s a method that uses a plastic storage tote with insulated cushions. You could easily make your cushions using old pillow cases if you aren’t much of a sewer. They include the directions as well as some real use examples.

Walkerland’s DIY Retained Heat Cooker

If you want to make one as shown in the main photo, here’s how we did it. Take a wicker basket and line it with a double folded heavy wool blanket. Line this with an old towel. When the contents of your pot have been brought to a complete boil, place the pot in the basket, tuck the towel all around it, then tuck the wool blanket around that. I used another basket as the lid but you could add another blanket or a piece of wood (maybe a big cutting board) instead.

Pre-Made Thermal Cookers

If making your own thermal cooker isn’t of interest you can find several styles on-line.

Wonderbag

Wonderbag is a simple yet revolutionary non-electric, portable slow cooker. The Wonderbag’s insulation allows food that has been brought to the boil to continue slow cooking or warm while in the bag. You can find it here(Amazon Link)

Modern thermal cooker

There are quite a few choices for modern thermal cookers including this one that has really good reviews: Thermos Nissan CC-4500P Thermal Cookware and Carry, 4.5 Liters. Find it here(Amazon Link)

Important Tips

Food safety is essential so be sure to understand the essentials when using a slow/thermal cooker

• Boil First: Make sure the food is brought to a full boil before placing it into the hay box.

• Safe Temperatures: Be careful. Do not allow the food to cool too much so that it becomes a health hazard. Food should be kept above 60°C.

• Always soak Your beans. You should not use dried (unsoaked) pulse vegetables because they may not cook thoroughly.

• Suggested cooking times: You should avoid opening the hay box cooker. Opening it will lower the temperature. This means that you might have to reheat the pot and start again. Here’s a link that provides cooking times for a variety of recipes.

Recipes

Thermal Cooking Recipes – A website dedicated to thermal cooking recipes

Thermal Cooker – A website dedicated to thermal cooking
Resources

The Fireless Cookbook (1913) Details how to use a fireless cooker along with recipes.

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