|Boiling Point No. 43 - Fuel Options for Household Energy (ITDG - ITDG, 1999, 44 p.)|
by Dean Still, Aprovecho Research Center, Center, 80574 Hazelton Road, Cottage Grove, Oregon 92424 USA
Une bo a isolation pour la conservation d'rgie
Le principe des boites solation est de conserver la chaleur dans la marmite une fois que la nourriture a chauff Cet article examine quelques designs et donne des instructions sur la durafin que la cuisson soit effectudans des conditions saines.
Hayboxes (sometimes called fire-less cookers) work by keeping as much heat as possible inside the cooking pot once the food has been heated up. The heat held within the food, water, and pot is used to continue the cooking process.
Using a haybox can save a lot of energy. After boiling food for a few minutes, the hot pot is placed inside an insulated box, where it finishes cooking. The retained heat is enough to finish cooking the food to completion; a haybox does all of the simmering for us, saving not only energy but effort as well.
A haybox also makes cooking much easier. The cooking pot does not have to be guarded against boiling over or scorching. Foods such as rice, beans, pulses, stews, or vegetables, are boiled up in the usual way and put into the haybox for several hours, from where they come out hot and ready to eat.
Hayboxes have been used for centuries in different countries. They work by insulating the pot, thereby keeping food hot enough for cooking to continue.
The design is simple:
· Make sure there is plenty of insulation around the pot, especially at the bottom and top
· The pot should fit into the box as snugly as possible
· The lid on the haybox should make a good airtight seal
· If possible, separate the insulation from the moisture given out by the pot by using a waterproof membrane wrapped around the pot.
A wide variety of materials, besides hay, can be used for insulation. Examples of good insulators are: straw, rushes, hay, chaff, popped grain, wood shavings, sawdust, newspaper, fibreglass, feathers, cotton, sponge, fur, wood ash, charcoal, ground nut shells etc. Allow about four inches (10 cm) of wall thickness. If cork, laminated cardboard, crumpled aluminium foil or rigid foam (such as that used in buildings) is used, only two inches (5 cm) is needed.
One of the most efficient hay-boxes is made by filling the air space around the pot with cushions, held in place inside a box.
Another simple method is to use two boxes, one inside the other. The space between the boxes is filled with insulation. An insulated lid fits over the top. This works even better if the pot sits on a pot-rest, such as a piece of plywood or rigid plastic packaging foam.
Another type of haybox is made from a double bag of fabric lined with insulation. A drawstring closes the top. The neck of the bag should open wide so that the pot can enter and be taken out easily.
A haybox can be something very simple like a hole in the ground. The pot is placed inside the hole on a bed of insulation. It is wrapped in a skin or plastic or oiled cotton bag. The bag keeps moisture from wetting the insulation. The space around the bag is filled with hay, straw, small pieces of foam plastic used in packaging etc. and is covered by a closely-fitting cover that keeps the air out. The hole can also be made in a block of sand/clay on a raised platform so as to be more accessible.
Remember that earth is not good insulation. It does not contain little pockets of air. It is the air in the straw, for example, that slows down the passage of heated air and allows the pot to remain hot, and finish cooking. Wet straw loses a lot of its insulating qualities.
Simmering food in a haybox will take one and a half to three times longer to cook than on a cooking stove. Cooking a large amount of food works better than a small amount, as it holds the heat better. A tight lid on the pot helps as well. Using one quarter less water with grains is necessary, since less water is evaporated during cooking. It is helpful to wrap the pot in a towel before putting it in the haybox.
Cooking gets rid of dangerous bacteria in food, and to ensure that the same thing is true for haybox cooking, two things are very important:
· Make sure that the food is boiled for at least five minutes on the stove before putting it in the haybox
· Do not take the lid off the pot between boiling the food and putting it in the haybox as this could introduce bacteria. If the meal contains meat, then reboil it on the stove before eating, just to be sure.
Hayboxes save energy, reduce smoke and make life simpler, all at once.
Figure 1 Fill space around cooking pot with cushions
Figure 2 Two boxes with insulation between them
Figure 3 An insulated box resting on an insulated platform
Figure 4 A double bag lined with insulation