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Cooking

There are a few basic concepts involved in cooking, and in designing cookers that will cook as rapidly, efficiently and conveniently as possible. These include heat gain, heat loss, and heat storage.

Heat gain is the heat that actually enters the cooker from solar energy, either by direct sunlight, or through the solar energy released by burning wood and other potential fuels. Heat loss is heat that escapes through the means of heat movement discussed above.

For wood cooking, remember that smoke is uncombusted fuel. A very efficient fire is almost smokeless, which means that fuel and trees are being conserved, and that air pollution is minimized. To make a fire efficient, you want to keep the temperature of the fire as high as possible, above 600°C (1100°F). This means regulating and warming the supply of air, if possible. It may also mean insulating the combustion chamber, and using low-mass materials for building the stove so that the heat is contained and concentrated.

For cooking in general, you can save a lot of fuel (and cooking time) by cutting food into small pieces, grinding up grains, pre-soaking dried beans overnight, and using minimal water. The food will cook more quickly if steamed rather than boiled, because the water will absorb a lot of the heat. Always use a lid when cooking.

Hayboxes

A haybox is an insulated container which can make significant fuel savings - up to 70%! Just bring the food to a boil, place the pot inside the haybox, and cover. The haybox will contain the heat in the food so that it will continue cooking without using extra fuel. In terms of our three heat concepts, a haybox works by maximizing heat storage and minimizing heat loss. A haybox is ideal for foods with a high water content like soups, stews, rice, boiled eggs and more. Foods which lose a lot of steam on the stove can be cooked with less water using a haybox.

You can precook the beans and legumes in some recipes, such as chili, in the haybox before adding other ingredients, since some beans must be boiled for at least 10 to 15 minutes to make them safe to eat.

Hayboxes can also be used to raise bread or incubate yogurt or tempeh. Place a container of hot water in the haybox to keep the temperature up.

You can use a cooler as part of a haybox, but you will probably want to add more insulation. You can make a haybox from all sorts of local materials, such as a basket filled with dried grass and covered with a bag or pillowcase of dried grass on top.

Cooking times:

Haybox Notes:
Aprovecho’s Guide to Hayboxes and Fireless Cooking, by Peter Scott, et al. Aprovecho Research Centre. (Brochure)
Fireless Cooking, by Heidi Kirschner, Madrona Publishers. 1981.

Efficient Wood-Burning

We can save fuel, trees, time spent gathering wood, and also reduce air pollution by using fuel efficient stoves.

Stove efficiency is based on two main factors. One, an efficient stove converts as much of the energy in the wood as possible into heat. Two, an efficient stove transfers as much of the heat as possible into the food being cooked. If we say that a given stove is 10% efficient, that means 10% of the energy in the burning wood goes into the food.

Not all woodstoves are very efficient. Some lose enormous amounts of heat by heating up large metal bodies, which then lose more heat to the ground and air around them. If you want to boil a 2 kg pot of beans, there is no need to heat up 300 kilograms of steel as well.

We will look at open fires, which can be between 8% and 18% efficient, or better, depending on the skill of the fire builder, the type of fire, and the windiness. We will also look at the Winiarski Rocket Stove, which can be more than 24% efficient, and the Dona Justa Stove, which can be more than 40% efficient. Please exercise caution and be safe when building fires or stoves.

Open Fires

Building an open fire

To build a fire, you want to start with very fine, dry pieces of flammable materials, called “tinder”. This could include moss, shredded paper, birch or cedar bark, or wood shavings. This material is the easiest to light. On top of that you loosely stack larger materials, “kindling”, such as pencil-diameter sticks and twigs or rolled-up newspaper. Then on top of that you put the largest pieces of wood, the “fuel”. You can also make a “fuzz-stick” with your knife by making wood shavings from a stick, and leaving them attached. In very wet weather, you can split open a log which is dry inside, and make “fuzz” from the interior.

There are two easy ways to stack the materials when starting a fire, “log cabin” or “tipi” style. A log cabin pile has the tinder at the bottom inside, and the kindling stacking criss-crossed, as shown. A tipi style has the sticks leaning into each other, or some with their ends stuck into the ground for stability. One advantage is that the sticks will fall into the fire as it burns. For both types you need to leave spaces for air flow. Firemaking is a skill that takes practice, and you’ll get better and better at it as you do it more.

Three stone fire

If you have long logs for fuel, don’t waste time and energy sawing or chopping them. Just put three large stones around the fire to reflect and retain heat, and then stick the ends of the logs in. As they burn, push them in further and further, until they are gone.

There are a lot of ways to cook on an open fire. You can place a grill on top, and cook meat or some vegetables. You can place pots or pans on the grill. You can hang pots from a “crane” or “spit”. Just drive two forked sticks into the ground, and place another stick between them.

If you are more of an expert at building up a coal bed, you can rake the coals out of the fire, and cook meat or vegetables right on top of them.

In very improvised circumstances, you can make a hole in the ground and line it with some waterproof membrane. Put in water (and food). Then heat rocks in the fire and drop them into the water or “stew” so that it boils.

You can also wrap food (such as potatoes) in aluminum foil, and place them near the fire, in the coals, or even bury them in the coals of the fire and cook them overnight. If you don’t have foil, you can cut the ends off of two aluminum cans, place the food in one, and then jam the other over as a cover.

Another improvised way of cooking is to make a fire in a pit, and burn it down to a coal bed. You may want to place rocks inside as well. Cover the coals with a thick layer of non-poisonous leaves. Then put on a layer of the food you want to cook, then another layer of leaves, and then dirt or sands as a cover. The heat and steam will be trapped inside, cooking your food.

Remember, never use rocks from a riverbed or other wet place to put in or near your fire. They may have water trapped inside, which could boil and cause the rocks to explode.

Hearth variations

The efficiency of the open fire drops a lot when it is windy. There are a number of ways to deal with this. You can lay two logs down on either side of the fire, or make a “U” shaped hearth with rocks. Wind blowing into the hearth will feed the fire with air. You can also dig a shallow trench a few feet long, about a foot deep, and wide enough for your pots to straddle the opening.

Fire hole

A bit more elaborate, and probably the best style of fire for high winds, is this fire hole. Dig a U-shaped hole, as shown, and start a fire in one end. You can feed in fuel through the other. Place your pot, elevated on sticks to allow air flow, over the side with the fire.

Efficient Woodstoves

There are a lot of different designs for improvised stoves out there, some better than others.

You can make a very simple improvised stove with a metal paint can. Remove the lid, and punch several large holes at the bottom of one side and the top of the other. Turn the side with the holes on the bottom into the wind, and place your pot on top.

However, there are more efficient stoves to use. We will look at two stoves designed by the Aprovecho Research Center, in Oregon.

Winiarski Rocket Stove

The brilliant Rocket Stove was developed by Dr. Larry Winiarski and the Aprovecho Research Center.

This excellent design is a combination of a number of design principles:

·Insulation around the fire keeps the fire burning hot (above 600°C or 1100°F), which is more efficient.
·Insulation around the chimney increases the draft, which provides a constant supply of air.
·Low mass materials are used, so that the heat produced is absorbed by the food cooking instead of the stove.
·Wood burns at the tip, and wood is shoved into the fire, controlling the burn rate and reducing smoke.
·The air/fuel mixture is controlled, since too much air will only cool the fire.
·A skirt around the pot maximizes heat contact and transfer into the food.
·Cooking occurs directly on top of the chimney for efficient heat transfer. This is possible because the stove burns at high temperatures and is nearly smokeless.

The Rocket stove design is a very versatile design which can be improvised with a variety of different materials.

The heart of the stove is an elbow-shaped, insulated combustion chamber. The fuel, in the form of sticks or narrow pieces of wood (or even tightly rolled-up paper, if that’s all you have), is fed into the fire on the shelf, as shown. The air enters into the fire underneath the shelf. Because the combustion chamber is insulated, the fire can get very hot, and burn very efficiently.

To build a rocket stove, you will need a larger housing container, such as a coffee can. Make a hole to put the fuel in through.

For the elbow-shaped chamber you can use stove-pipe, scrap metal, or a pair of cans put one into the other. An improvised can chamber will last for about 3 months. Plastering the inside with castable firebrick will improve the lifespan. A taller chimney will be more smokeless. However, a shorter chimney will let the flame touch the bottom of the pot, and transfer heat more efficiently to the food.

Place the elbow joint inside of the larger container. You may need to place a brick or other material underneath to help keep the placement. Then fill the space between the elbow and the housing with fireproof insulation. This insulation could include wood ash, vermiculite, perlite, pumice rock, dead coral or air-trapping layers of aluminum foil.

You will need to make a shelf for the fuel wood to put in the elbow joint. You can pound a can flat, and cut it to fit.

You may want to make a wire grill to place on top of the housing, to rest the pot on.

Adding a metal skirt will also help the heat transfer tremendously, because it will force the hot gases to rub against more of the pot, as shown. The skirt should be about 1 cm from the pot.

Starting a Rocket stove is a little bit different from starting an open fire. Try putting your tinder on the shelf, igniting it, and then pushing the fuel in.

Dona Justa Stove

The Dona Justa stove is an extension of the rocket stove concept, and is another Aprovecho design. It is designed to be used inside, so there is a long chimney which vents the (minimal) smoke outside. The hot gases from the combustion chamber move up and across the bottom of a metal cooking surface. The underside of this passage is insulated to retain heat. The smoke then goes up the chimney and outside.

The downside for efficiency of this stove is that the metal cooking surface will release heat into the air wherever it is not touching a pot. You can improve the efficiency of this stove by making holes in the surface so that the pots can be put into the channel where the hot gases travel. This contact improves heat transfer. You can build a form-fitting channel, as shown, so that the gases are forced to go as tightly as possible against the pots.

See the following page for an illustration.

Solar cooking

Heat gain in solar cooking comes from a few main sources:
•The Greenhouse effect, where light travels though the glass or transparent plastic and hits objects inside, but the heat is unable to get back out through the glass.
•Glass orientation (glazing) is another consideration. More light will travel though the glass if it is at a right angle to the light coming in. Otherwise, part of the light will reflect away.
•Reflectors direct more light towards the pot or oven.

There is a wide variety of creative solar collectors for use in cooking, and I encourage you to check out different varieties to see what might work best for you.

Tips for solar cooking:
•Use dark pots with lids.
•Don’t open the pot while cooking. The temperature is lower than other types of cooking, so you don’t need to stir because sticking and burning is rare.
•Put the food on early, because solar cooking takes longer than other sorts of cooking.
•Adjust the solar cooker regularly to follow the sun.

If you double the scale of a solar cooker design, you increase the amount of light captured by a factor of four.

For solar reflectors, you can use whatever materials you have available to you. You can paste aluminum foil onto corrugated cardboard. Make sure that the foil is on smoothly because wrinkles will impair the focus. Contact cement seems to work well as an adhesive, though other improvised glues will be covered in future writings. You can also use polished sheet aluminum or other polished sheet metals, or aluminized mylar.

Simple folding solar cooker

This is the simplest, most portable, and lowest temperature cooker of the solar cooker designs here. However, it can be built quickly and easily out of basic materials, and will still work well on brighter days or in brighter latitudes.

If you place a black pot in a clear plastic bag as shown, you will have better heat-retention. A simple wire frame can prevent the bag from touching (and melting) on the pot. It will also keep the pot off of the ground, reducing heat losses from conduction.

This solar design (as well as the others) can be used to boil or disinfect water for safety (see Treating Water, p.9)

If you have time and access to materials it might be a good idea to build a larger and more effective model.

Solar Oven

This is the next simplest design. It requires a small glass pane, which can be salvaged from any number of sources. This design is derived from the work of Dr. Maria Telkes, a 1950’s solar pioneer and appropriate technologist.

You’ll need to make an insulated box like the one in this illustration. For improvised insulation, you can use alternating layers of aluminum foil and corrugated cardboard. You can also use wood ash, charcoal, etc. The top of the box is an angled window, and the back has a door to access the food. You can use plywood for the main structure of the box, or any other improvised material.

To decide the ideal angle of the glass for this cooker (and the solar still in the section on water) take your latitude and subtract it from the number 90. This is the noontime average annual angle of the sun in the sky. Add 23.5 to get the sun’s noontime angle on the summer solstice, and subtract 23.5 to get the sun’s noontime angle at winter solstice. Pick the best angle, considering that the glass would ideally be at an angle of 90 degrees to the sun. If you mostly cook in the summer, then you will want to use an angle between your average and summer solstice noon-time angles.

Ideally, the interior of the oven is lined with black-painted metal, to absorb as much light as possible and turn it into heat. Use water-based paint. (Before using your oven, let it “bake” empty in the sun for a couple of days to get rid of harmful gases from the paint.)

Then mount reflective panels as shown to reflect the sunlight into the oven. An angle of about 30 degrees from the sun (or 120 degrees from the glass), as shown, works best.

You’ll want to have a relatively easy way to adjust the position of the collector to follow the sun. The oven illustrated is simply mounted on skids. You’ll probably want to adjust it about every 15 minutes or so. Experiment to see what works for you.

Parabolic cooker

The parabolic cooker is a bit more complicated, but works quite effectively if you can manage it. You can fry on a parabolic cooker. Here we will look at a few variations on the basic idea.

The basis of the parabolic cooker is the parabola, a curve which, as illustrated, will reflect incoming parallel rays (such as from the sun) onto a small point. This permits very high temperatures to be created. For this reason, there is an important warning: Do not look directly into the reflected sunlight. This could cause severe eye damage. For safety, make sure to put the focal point inside the cup of the reflector.

You can draw a parabola using a right-angle as shown at right, without any knowledge of mathematics. (Geometrically, a parabola is defined as a curve on which any point is the same distance from the focal point as it is from a base line, the “directrix”.) Place the nail where you would like the focal point to be. Always keep one arm of the right-angle against the nail, and the corner against the baseline. Start with the corner directly below the nail. Move the corner a little bit away from the centre each time, and draw a line from the baseline out towards the edge of the cardboard. Eventually you will have many lines which intersect along a curve. This thick composite curve is your parabola.

If you want, you can use the concave (cave-shaped) section of the parabola as a frame template for a collector like the one shown in the top right corner of the illustration on the following page. This is appropriate for heating water, or for cooking hot-dogs or shiskabobs. However, you may get a lot of heat loss from the food being cooked, since it is exposed, and has a lot of surface area. This loss can be reduced by sheltering the collector from the wind, and insulating the side of the food facing away from the collector.

If you use the convex section of the parabola, you can rotate it in clay to produce a mold, or make a framework like a spider’s web, with radial, parabolic arms, and then curved struts connecting them.

Once you’ve built your reflector, you will need to build a base which you can mount it on to rotate the reflector to follow the sun. You will also need some kind of pot holder, like the grille shown. Also, an alignment indicator (which can be as simple as the circle with a post shown) will help you to line up your parabolic cooker with the sun. Just mount the post at 90° to the cooker. When the post casts no shadow, the collector is properly aligned.

If you make a template out of corrugated cardboard, you can fold it in the middle, as shown in the centre of the illustration, to make a template for a folding parabolic collector. This will not be as accurate as a true parabola, but it will probably be good enough for cooking. Lay a piece of aluminized mylar, or other shiny, relatively stiff material (even thin, polished sheet metal) over the template. Cut off the excess and leave tabs for attaching the other segments, as shown. You can copy the other segments from this original. Make the angle that you fold the template appropriate to the size of material you have available to you, but make sure that it will divide evenly in a circle. For instance, if you want to make a folding collector with six segments, divide 360° by six (to get 60°) and angle the two halves of the template 60° apart. For eight segments, use 45°, and so on.

It’s worth noting that satellite dishes are also parabolic reflectors (for radio waves.) So if you can find one of the appropriate size (and especially one which can be adjusted for tracking) you may be able to cover it in reflective material and use the existing structure.

You can make the parabolic reflector out of a number of materials. They don’t have to be aluminum foil - polished metal will do, and mirror pieces are even better.

In general, collectors larger than 2 metres (6.6 feet) across are considered unwieldy, but you can manage it if you have a sturdy mounting and avoid high winds.

If a parabola is too difficult, for boiling water you can also make a simple conical cooker. Cut a shape out of sheet-metal, or cardboard to glue aluminum foil on to. Remove 105.5° of the circle. Bring the edges together, as shown, to form a cone. The focus of the collector is a line along the center of the cone. You can use a black pipe of water as the container, or make a long black metal sleeve, and put the kettle in the top.

Solar Cooking References:
www.solarcooking.org
Capturing Heat booklets One and Two, by Dean Still et al, Aprovecho Research Center. (www.aprovecho.net)

Biodigested Methane

Methane produced by decomposition in a chamber may be a suitable source of cooking fuel for some people. Essentially, manure, straw, and other organic materials with a high energy content are allowed to decompose under controlled circumstances. It’s like composting, but without air.

This may be a good option for people who have limited access to firewood, but plenty of biomass.

The subject is too extensive to cover in this excerpt booklet, although it will eventually be covered in the full book.

Cooking Notes
There are a number of improvised cooking measures that aren’t covered here, largely because of their dependence on petroleum-derived fuels. However, those options can be excellent temporary or emergency measures. Semi-solid fuels like paraffin, gelled alcohol or “Sterno” cans are safe and easy to use, although they don’t generally burn as hot as other sources. You can find gelled, spill-proof fuels in camping or hardware stores, sometimes sold as “Canned Heat,” or “Warming Gel,” and some “environmentally friendly” products are made from sugar cane by-products. Liquid fuels like denatured alcohols or methyl hydrate can be used relatively safely in improvised stoves of a different type than here. You can use a simple shallow cup with a small amount of alcohol for quick burns, or a “plumber’s stove,” a can filled with cotton balls and alcohol. Liquid fuels like kerosene and gasoline can be used for fuel, but are volatile and difficult to use safely, since they can explode, and produce dangerous gases in an enclosed area. For more info on alcohol burning improvised stoves, look at:
http://home.comcast.net/~agmann/stove/Stoves.htm

It is also possible to prepare most grains and seeds without cooking them by soaking and sprouting them. Once the grains sprout they can be eaten raw. All you need is dried seeds, clean water, and a place to sprout the seeds. You put the seeds in a screen bag, a jar with a cloth over the mouth, or even a simple tray. Rinse the seeds in fresh water several times a day to keep them wet, and let the excess water drain off. In a few days the seeds will grow into sprouts. You can find out more about raw foods on the internet at websites like www.living-foods.com.

Please remember that many beans can not be eaten safely without cooking, and that sprouting is only safe if clean drinking water is used.

Capturing Heat booklets One and Two, by Dean Still et al, Aprovecho Research Center.
The Aprovecho “Fish Camp” Stove book, by Dean Still.
The Aprovecho Research Center website is www.aprovecho.net. Check out their stove page at http://aprovecho.net/at/atindex.htm.
Fieldbook for Canadian Scouting, Boy Scouts of Canada, 1986
The Journey to Forever Woodstove page:
http://journeytoforever.org/at_woodfire.html
The Home-Made Stove Archives, at:
http://wings.interfree.it/html/main.html
The extensive Renewable Energy Policy Project’s Biomass Cooking Stoves page:
http://www.repp.org/discussiongroups/resources/stoves/

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