A large number of the world’s poorest people spend a third of their income on fuels such as kerosene or paraffin. Others, invariably women, have to trudge for hours each day – often risking attack or rape – to fetch firewood or dung, which increases deforestation and denudes the soil. Burning the fuel in their inefficient stoves produces toxic smoke that kills more than two million people – mainly women and children – a year, and emits carbon dioxide and black carbon, the two main causes of global warming. Attempts to introduce solar cookers have failed because people cook at night, after the sun has gone down.Unfortunately, the bag is too expensive for the people that need it to actually buy it. The makers are hoping to get a government subsidy. (Interestingly, this design is obviously based on a device called a "Wonderbox," also developed in South Africa, but several decades earlier--clearly, the idea mentioned in The Telegraph article above is not original, not even as to the name or the type of insulating material used).
The idea first came to Sarah Collins, a Durban “social entrepreneur”, during power cuts in 2008. She remembered how her grandmother had surrounded her pans with cushions to keep them cooking when taken off the stove. She tried it, found that it worked, and wondered if it could help the poor.
She later mentioned the idea to Moshy Mathe, a formidable, “traditionally built” social activist while sitting with her on an aeroplane. Moshy suggested replacing the cushions with a padded bag and together they went on to develop the lidded Wonderbag, covered in African textiles and insulated with recycled polystyrene.
Its users can heat cassava on a stove in just half an hour, instead of eight, placing it in the bag to finish off, and there are big reductions in cooking times for rice, stews, beans and root vegetables (each bag comes with recipes for such delicacies as tripe, “supper pap”, and chicken feet). It works on the same principle as the old hay box, or the Bushman practice of burying food to continue cooking.
All of the bogus PC, "caring about people" comments aside (how caring can they be when they copy other people's ideas and pass it off as their own), the article raises an important issue, which is during a grid-down situation, you may have limited access to fuel. One way to conserve fuel is to get a cooking pot and its contents up to cooking temperature, and then move the pot to an insulated container to simmer and continue cooking.
As noted in the article, the idea is similar to the old-time "hay box." Constructing and using a "hay box" is discussed in some detail in Cody Lundin's book, When All Hell Breaks Loose. (Amazon link here). Mr. Lundin notes that using a hay box, "[i]ts fuel savings, depending on the type of food and how much cook time it requires, can be from 20 to 80 percent!" Id., pp. 330-331. He explains:
The concept behind insulated cookers is simple. When food in a container is put near a heat source, the food climbs to the boiling temperature and then stabilizes. The food within the stabilized temperature then "cooks" for a given period of time. Any heat beyond the boiling temperature is merely replacing heat lost to the surroundign environment by the pot. When the container reaches it top temperature and then is removed from the heat source and placed in a super insulated box, the food inside continues to cook. In heat-retained cooking, food is brought to a boil, simmered for a few minutes depending on the particle size of the food, and then put into the hay box to continue cooking.Id., p. 331. Lundin recommends simmering (i.e., over the fire or stove) small grained foods, such as rice, for 5-6 minutes; dried beans (preferably presoaked and drained) and whole potatoes for 15-18 minutes; and red meats for 20-30 minutes. He cautions that meats should be reheated over the stove or fire prior to serving. He also advises that you practice and experiment with this method since it obviously will vary according to the insulation you use, how tightly it fits around the containers, the type and size of containers, and so on.
Plans for building an insulated cooking box similar to the Wonderbox can be found here. Cooking ideas here.
There was also a discussion on the Zombie Squad forum about using a Thermos for insulated cooking. (See here and here). Apparently, specific vacuum flask systems are available for insulated cooking. (Wikipedia article here).
Update (11/4/2014): The Approaching Day Prepper takes a look at the Wonderbag.