February 24, 2017

More Thermal Cookery

The old stove on left features a "thermodome" that lowered over the cooking pot after the heat was turned off.


OK, after our recent experiment, I admit I am obsessed with thermal cookery. Or to be more exact, I have always been obsessed with energy efficiency.

The efficiency of a modern electric cook stove has a thermal efficiency of about 15%, meaning that 85% of the energy is wasted. This is partly because converting fossil fuels to electricity produces an energy efficiency of 20-45%, depending on the power plant.

There is much room for improvement, since this is about the same efficiency of an open fire, a truly ancient technology.

One way we can improve on the efficiency of the cooking process is by using thermal retention which prevents heat loss to the point that food continues cooking without additional energy.

Using thermal retention to cook foods can save up to 80% of the energy required for normal cooking, depending on the thermal cooker and heat source used, and on how long it takes to get the hot pot into the cooker.

An electric stove, when used with a thermal cooker, doubles its efficiency to about 26%, which still is not that good, but much better than the electric stove alone.

This old stove shows a "thermowell", a built-in thermal cooker. With the pot shown, one could cook three different foods in one pot. 

Around the early 1900s, kitchen stoves were designed with heat retention features, and were called "fireless cookers". Some old stoves had insulated bells that lowered over cooking pots to retain heat (marketed as "thermodomes"). Others had thermal cookers or insulated "wells" built right into the cooktop that pots could be lowered into for thermal cooking.

One such stove boasts of a "New and Improved Thermowell" that does one hour of cooking with only 10 minutes of energy use. Another was sold as the stove "that cooks with the gas turned off".


A 1950s era electric stove that still featured a built-in thermal cooker.

As power became more abundant, such efficiencies were lost. The good news is that we can re-introduce this energy saving technology quite easily in our modern kitchens with materials we may already possess.

Sample Cooking Times In A Thermal Cooker

White rice: 5 min on heat, 1-2 hours in cooker
Brown rice: 10-15 min heat, 2 hours in cooker
Potatoes: 5-10 min heat, 1-2 hours in cooker
Creamed soups: 2 min heat, 1 hour in cooker
Dried beans (soaked): 10-15 min, 3-4 hours in cooker


It is hard to imagine a more cost-effective technique to lower energy use than a homemade, DIY thermal cooker. See our post about trying out our first DIY thermal cooker HERE.

February 22, 2017

DIY Thermal Cooker

Camping cooler? No. DIY Thermal Cooker in action.


When it is easy to use a seemingly endless supply of energy, we tend to use more than we need. When using energy efficiently is more difficult or time consuming, the tendency is to use it more thoughtfully and frugally. That is what thermal cookery is all about.

Also known as "retained heat" cooking, this ageless method has been around since humans discovered that insulating a pot of hot food with banana leaves, or buried in the ground, is a great way to use energy more efficiently.

A thermal cooker is essentially a slow cooker without a power cord. Of course one can buy all manner of fancy thermal cookers, but this method hasn't been used for thousands of years because it is complicated or expensive.

The thermal cooker is a perfect DIY experiment in simple living, and one that Linda and I investigated this week in the NBA Simple Cooking Research Laboratory, or, our "kitchen". Armed with white lab coats and oversized magnifying glasses, we started with sorting/rinsing 3 cups of pinto beans, destined to become one of our staples, refried beans.


Bringing dried pinto beans to a boil and 10 minute simmer on the electric cooker.

On the stove top we brought the water-covered beans to a boil, then simmered covered on medium heat for 10 minutes.

After 10 minutes we took the bean pot off the stove and immediately put it into our DIY Thermal Cooker, a camping cooler stuffed with a large blanket. You can also use straw, sawdust (shouldn't that be "treedust"?), balled up newspaper, old pillows, an old sleeping bag, or any other insulating materials.











The blanket was stuffed firmly around the pot, lid closed, then left to continue cooking overnight. The next morning the still warm beans were done and ready for flavouring and mashing to make refried beans.

The vessel used for the cooker can be about anything as well. It can be built in a cardboard box, laundry basket, hole in the ground, or a heat retention bag sewn specifically for this purpose.


Example of heat retention bag for thermal cooking.


Why waste energy when there is an easy way to use it more efficiently? Perhaps because that more efficient method may not be as convenient. Unfortunately, convenience always entails unintended consequences, like excessive waste. But the worst of it is that convenience-at-all-costs leads to a less beautiful, self-sufficient, mindful life.

Rather than convenience, I like to think about what the most efficient and life-affirming way of doing things might be, even if that means something I do is "harder" or more difficult. Imagine life if we never did things that are hard to do. Just because something is harder, doesn't mean it isn't beneficial.

Conducting experiments in living more simply, and trying out new things, is not inconvenient, it is challenging, rewarding and a great deal of fun. The DIY thermal cooker was a good example of that principle. We are adopting this energy efficient method of cookery in our kitchen. I mean, laboratory.

See more on thermal cookers HERE.
"Cooking, ultimately, is about heat, how heat enters the food and what happens to the food when it enters." 
- Cooking For Engineers




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