Be Better Prepared with a Fireless Cooker

1 / 2
One of the major drawbacks of using fire to cook food is that much of the energy isn't trapped to heat the food and is wasted.
2 / 2
“Green Wizardry,” by John Michael Greer, is a valuable resource for anyone concerned about decreasing our dependence on an overloaded industrial system and making life a great deal less traumatic and more livable.

Green Wizardry (New Society Publishers, 2013), by John Michael Greer, proposes a modern mage for uncertain times, one who possesses a vast array of practical skills gleaned from the appropriate tech and organic gardening movements forged in the energy crisis of the 1970s. From the basic concepts of ecology to a plethora of practical techniques such as composting, green manure, low-tech food preservation and storage and more, Greer provides a comprehensive manual for today’s wizard-in-training. The following excerpt from Lesson 24, “Hayboxes and Sunboxes,” addresses the problem of using non-renewable fuel to cook our food and introduces us to fireless cookers.

You can purchase this book from the MOTHER EARTH NEWS store:Green Wizardry.

The principle of conserving differences is central to the appropriate tech toolkit, and it can be applied in a dizzying variety of ways. One good example is a simple, resilient technology that helps solve one of the most serious problems that poor people face now and the rest of us will be facing shortly. The technology was common all over the industrial world a century ago, and you’ve probably never heard of it.

Let’s start with the problem: cooking fuel. Most foodstuffs are safer to eat and easier to digest when they’ve been subjected to heat, which is why every human culture everywhere on Earth has the habit of cooking most meals. The one drawback is that the heat has to come from somewhere, and usually that requires burning some kind of fuel. Anywhere outside today’s industrial world, fuel doesn’t come cheap, and in most poor countries the struggle to find enough fuel to cook with is a major economic burden, not to mention a driving force behind deforestation and other ecological crises.

The obvious response, if you happen to think the way people in the modern industrial world think, is to deal with fuel shortages by finding and burning more fuel. That’s exactly the thinking that got us into our current predicament, though, so it’s worth looking at other options. To do that, we need to start with the thermodynamics of cooking.

Imagine, then, a saucepan on the stove cooking rice. It’s a metal container with a heat source under it, and inside it are two cups of water and a cup of grass seeds — that’s “rice” to you and me; the goal of the operation is to get enough heat and moisture into the grass seeds that will allow your digestive system to get at the starches, sugars, B vitamins, and other nutritious things inside the seed. So far, so good, but this is where a familiarity with the laws of thermodynamics comes in handy, because there’s a prodigious waste of energy going on.

Trace the energy flow and you can watch the waste happen. The energy at the heat source is highly concentrated; it flows, with some losses, into the metal saucepan; some of it flows through the pan to the water and rice, where it does the job of cooking, but a great deal of the heat gets into the sides and lid of the pan, and radiates away into the air, so that a great deal of the energy in your cooking fuel is being used to warm the surrounding air. This is all the more wasteful in that your rice doesn’t need a huge amount of heat once the water’s been brought to a boil; a very gentle simmer is more than enough, but to produce that gentle simmer a lot of fuel gets burnt and a lot of heat wasted.

Here’s an experiment for you to try. Get a cork mat larger than the bottom of the saucepan you use to cook rice, and a tea cozy. What’s a tea cozy? An insulated cover for a teapot, designed to keep the tea in the pot good and hot while you work your way down from the first relatively pallid cups off the top to the good stuff, roughly the color and consistency of road tar, down at the very bottom. The kind of tea cozy you want has a slit in one side for the handle of the teapot, and one opposite it for the spout, and it needs to be large enough to pop over the saucepan with the saucepan’s handle sticking out through one of the slits; the more insulation it has, the better.

Got it? Okay, get your pot of rice started; when the water has reached a good, fierce boil and you’ve put the rice in, cover the saucepan tightly, take it off the heat, put it on the cork mat and pop the tea cozy over it. Leave it for a little longer than you would normally keep it on the stove, and then serve; if you’ve followed the instructions, you should have perfectly cooked rice with a fraction of the fuel consumption you’d otherwise have had.

Hayboxes and Solar Box Cookers

If you’ve done the experiment, you’ve just learned the principle behind the fireless cooker. In America, they were often called “hayboxes,” because that’s what the old-fashioned version was: a wooden box stuffed full of hay in such a way that there was a space for a pot in the middle, and a pillow of cotton ticking, stuffed with more hay, that went over the top. A hundred years ago, you could get elegant models from department stores that had porcelain-coated steel cases, rock wool insulation, and easy-to-clean metal liners with pots sized to fit; the best models had soapstone disks you could stick in the oven during the day’s baking, then drop into the fireless cooker, put a pot of soup or stew on top, and have it piping hot for dinner six hours later.

I’ve never seen an old-fashioned fireless cooker. Here in America, most of them were turned in during the big scrap metal drives in the Second World War, though they were still in use in some corners of Europe in the 1940s and 1950s. Still, the technology is simple enough that even the least capable home craftsperson can put one together in an hour or two. My spouse and I have two of them, a portable version in a wooden box and a rather less portable version built into a piece of furniture; both of them were built using a slightly improved version of the basic haybox design, with polyester quilt batting for the insulation and cotton ticking covering the batting to keep it clean. Both of them work extremely well; the technology could probably be improved by skillful engineering, but they were cheap to make, cost nothing to use or maintain, and allow us to cook with a small fraction of the fuel that has to be used for stovetop cooking.

Those of my readers who have been paying attention may be wondering by this point if there’s some way to get diffuse heat from sunlight to power a haybox. There is, and the result is called a solar box cooker. This is one of the triumphs of the appropriate tech movement: an insulated box, equipped with a window through which sunlight falls, which is entirely capable of cooking your dinner on a sunny afternoon. You can find plans for solar box cookers online or in a dozen easily accessible books, and you can make one out of cardboard, newspaper, aluminum foil, glue and a piece of discarded window glass. Placed in direct sunlight, it will easily get up to oven temperatures and cook your meals for free. It can also be used to purify tainted water, sterilize bandages, or do anything else that 300 degrees to 400 degrees Fahrenheit of steady heat will do for you.

The solar box cooker also has the not inconsiderable advantage of teaching three of the basic rules of working with solar energy in a way that most people find easy and intuitive to grasp. Rule #1 is the greenhouse effect: energy from sunlight that passes through glass and is absorbed by something inside the glass tends to get trapped there because glass is transparent to visible light but opaque to the infrared wavelengths that radiate out from warm objects. Rule #2 is the thermal mass effect: some materials absorb heat better than others, and if you put something with a high capacity for heat absorption in the presence of a heat source — say, a pot of beef stew in direct sunlight — it will soak up heat that can then be put to work. Rule #3 is the insulation effect: some materials resist the flow of heat better than others, and if you surround your thermal mass with a bunch of insulation, the heat absorbed by the thermal mass will stick around longer and do more work. Keep these three rules in mind, and most of what we’ll be covering in the lessons ahead will be much easier to follow.

There are several standard designs of solar box cooker. The simplest looks exactly like what the term suggests, a square or rectangular haybox with a pane of glass on top. A hinged lid covers the glass when the box cooker isn’t in use; it has tinfoil on the underside, so that when you’re ready to use the box, the lid can be propped up at an angle to reflect more sunlight into the box. Yes, you can make one out of cardboard and newspaper in about an hour, and yes, you can then set it out in the sun and cook your dinner with it.

The more complex designs put the glass pane at an angle, to increase the amount of sunlight that gets in, and they have more reflecting surfaces for the same reason. The fanciest look like metal flowers or props from 1970s science fiction movies. These, you don’t want to make out of cardboard because they generally get hot enough inside to set cardboard on fire. I’ve seen some very impressive solar box cookers on the fancy end of things, with mirrors that would do justice to a telescope and elegant arrangements to track the sun, I’m by no means certain that all the additional complexity provides enough improvement in performance to make the effort worthwhile, but the experiment is worth making.

Two other developments of the same basic approach are also worth mentioning. The first was invented by one of the patron saints of green wizardry, the redoubtable 19th-century French solar energy pioneer Augustin Mouchot. Tasked by the French government with coming up with solar technologies for the French colony in Algeria — which had a surplus of sun and, at least in Mouchot’s time, a shortage of most other energy sources — Mouchot invented, among other things, a solar cooker for units of the French Foreign Legion stationed there. The device was simplicity itself — a cone of metal, reflective on the inside; a cylindrical steel cooking chamber that went up the centerline of the cone; and a tripod stand. Mouchot’s solar cooker was collapsible, weighed less than forty pounds, and cooked a pot roast to a nice medium rare in under half an hour. It remained standard issue for French troops in North Africa for decades. I have no idea if any examples survive, but it’s 19th century technology, so an enterprising metalworker ought to be able to knock one together fairly easily.

The other device I have in mind comes from the other end of the solar cooking spectrum, but it’s as elegant as the Mouchot cooker and even more portable. The Umbroiler was invented by American solar pioneer George Löf and marketed for a while in the 1960s and 1970s. It’s exactly what the name suggests: a sturdy umbrella frame with silver metalized cloth in place of the usual fabric, a grill in place of the handle, and a tripod on what’s normally the top of the umbrella and is the underside of the Umbroiler. It folds up like any other umbrella, but when you open it and point it toward the sun, you can cook anything from eggs to coffee on the grill. The original version was too expensive to be commercially viable, due mostly to the high cost of metalized fabric back in the 1960s; these days, that has changed, and since the patents have long since expired, a revival of the Umbroiler could make somebody with a sewing machine and basic metalworking skills quite a viable small business.

By now, I suspect, some of my more skeptical readers will doubtless be jumping up and down, eager to point out that solar cookers only work when the sun’s shining. This is, of course, true, but it’s also beside the point. Nothing in the appropriate tech toolkit is suited to every context — that’s one of the implications of that word “appropriate,” after all — and nothing ever again in human history will provide our species with the kind of instant, context-free torrent of energy we now get from fossil fuels. Once those are gone, the entire approach to technology that’s built on the assumption of abundant, highly concentrated, highly portable energy supplies goes away forever, and the approaches that will replace it are going to be less convenient, less portable, and less capable of ignoring the rest of the cosmos than what we’re used to.

What that means in practical terms is that a well-equipped kitchen in the deindustrial future will likely have a solar box cooker, which can be used on sunny days, and a small, efficient stove and fireless cooker, which can be used on cloudy days. It really isn’t that complicated, once you grasp the crucial point that a technology that relies on diffuse renewable energy sources doesn’t work the same way as a technology that relies on concentrated fossil fuels. Each form of diffuse renewable energy is well suited for some purposes and poorly suited for others; an effective application of renewables requires a locally appropriate (there’s that word again) mix of technologies to do what needs to be done to make human life viable and comfortable.

Read More from Green Wizardry:

Start a Compost Pile to Help Your Garden Grow
Bring Beneficial Organisms into Your Garden

Exercise for Lesson 24

As already mentioned, there are scores of books and web pages that explain how you can build a solar box cooker out of cheap or free materials. Your exercise for this lesson is to find a set of plans that suits the resources and skills you have, build a solar box cooker using those plans, and use it at least once to cook something. This isn’t just an introduction to an energy-efficient method of cooking food, though it is that; more important is the practical education you’ll get in learning how diffuse heat from the sun can be concentrated and put to work.

Reprinted with permission from Green Wizardry: Conservation, Solar Power, Organic Gardening, and Other Hands-on Skills from the Appropriate Tech Toolkit by John Michael Greer and published by New Society Publishers, 2013. Buy this book from our store:Green Wizardry.

Need Help? Call 1-800-234-3368