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Pans with Fins by Clive Savill et al.
When a pan is placed over a gas hob or fire, the gases move slower the closer they are to the pan. As combustion products and air are poor conductors, a slow moving cool layer of gas insulates the pan from the faster moving hotter gas. As metal pans, especially if filled with liquids, are good conductors, they will cool this insulating layer quickly. According to the author's invention, fins on the bottom of the pan are used to create turbulence and extract more heat from the hot gases. This should reduce the time and fuel needed to bring things to the boll and reduce the amount of fuel needed to maintain the temperature necessary to cook the food or heat the water. The fins should be of an acceptable strength so excessive care is not needed to avoid damage in use and should be of low volume so as to minimize additional weight and cost. Hence, a compromise is called for as a lot of thin fins would be the lightest and most efficient. Increasing fin height would bring Increasing efficiency with diminishing returns. The fins will probably be about a centimetre or two on an average size pan.
[top] [end]Haybox Cookers in RwandaBy Penelope Vincent-Sweet, B.P. 691, Butare, RwandaRwanda, a country the size of Wales in the mountains of Central-Eastern Africa, has a population of about six million, making it the most densely-populated country in Africa. A sustained programme of erosion control on its ubiquitous hills, together with tree planting (there is a Tree Day each year when every person should plant at least one tree), has helped halt and even redress the damage that the cutting- down of trees and the cultivation of Increasingly marginal (sloping) areas was doing to the fragile ecological balance. Nevertheless, the population continues to Increase, and one study has estimated the annual shortfall of wood (consumption minus production) at 4 million cubic metres (1). One result of wood's increasing scarcity Is the increasing use of agricultural residues for cooking fires, a practice which deprives the soil of organic matter and causes a decrease in yields. Since at least 95% of the population uses wood, either directly or as charcoal, as a cooking fuel, any reduction In the fuel needed for cooking has potentially a large Impact on wood consumption. The staple food In Rwanda Is the common bean, which, from the dry state, usually takes between 3 and 4 hours to cook - longer for old beans. Programmes seeking to encourage soaking of beans to reduce cooking time have had very little success, due to people's dislike of the resulting change in taste and colour. The impact of improved cookstove projects has so far been limited, and the vast majority of Rwandan women still use the three- stone fire. In the large towns charcoal Is more common, but less than 5% of the population live in the towns. There is by no means a universal awareness in rural areas that the supply of wood might be a problem, but in some areas people are realising that wood is becoming more difficult to find, and that there may be some point to saving wood. In the area I surveyed, nearly all the participants agreed it would be useful to save wood in the rainy season, as it is not always possible to go out to fetch wood, and the wood collected is wet. (None of the families questioned had a stock of wood to enable wet or green wood to be dried out for several days before use). [top] [end]The Haybox CookerIt is in this context that I have been introducing a "new" technique: the haybox cooker, used in Europe at times of energy scarcity. The principal is simple: the food is partially cooked in the normal way, then the pan is taken off the fire and placed on a heated stone in a large box containing hay or other insulating material. This retains the heat in the saucepan, allowing the food to continue cooking at a slightly lower temperature than on the fire. The total cooking time is slightly longer than normal, but once the pot is in the haybox there is no need to watch the fire or stir the pot, so the housewife is free to do other things. The food can even be prepared In the evening and left overnight In the haybox.[top] [end]The Rwandan HaybasketSince baskets are very common in Rwanda, we used these rather than boxes; any large container would be appropriate, even a hole in the ground. We use a strong basket plastered with cow-dung, dimensions about 50cm × 50cm.Cooking of beans begins as usual, with the addition of a flat stone (or several small ones) set to heat in the fire. The beans are boiled 45 to 60 minutes (80 to 100 minutes from the start of cooking), In the case of beans which normally take 3 or 4 hours to cook. After this time the cook tests the texture to check the grains are well swollen and partially cooked. Salt and further water are added to the cooking beans, as may be an accompaniment such as sweet potatoes or cassava. The basket is partially filled with Insulating material: straw, dried leaves or wood shavings. The heated stone is put into the basket on a layer of sand, held by a piece of broken pot or cardboard, or a banana leaf. The cooking pot, well covered with a lid or a banana leaf, is placed on the stone, and held in place by a cylinder of plaited rushes. A cushion of straw covers the whole, and it is left to cook for at least four hours. The temperature of the food after this time is usually between 70 degrees Centigrade and 80 degrees Centigrade, compared to a boiling point of 94 degrees Centigrade at 1800m above sea level. The larger the quantity of food, the better it holds the heat.
The haybasket is made with very simple materials: only the basket Itself and possibly the sack to make a cushion need to be bought. The stone can be an ordinary one picked up nearby, a brick, or a clay 'stone' specially made by a potter - which gives better results. A good weight is 1.5 to 2 kg. It is necessary, since water boils at 94 degrees Centigrade, to boil the beans for about 45 minutes before putting them in the haybasket, to be sure that the toxins found in raw beans, notably lectins (phytohaemoglutenin), are in-activated. [top] [end]On-Farm Trials[top] [end]ResultsThese trials were included in a programme of research on firewood economy with different varieties of beans and cooking methods, organised by Krista Dessert of the bean programme of C.I.A.T. (Centro Internacional de Agricultura Tropical) at the 'Institut des Sciences Agronomiques au Rwanda'. Here we will consider only the trials concerning cooking methods.[top] [end]ProcedureThe ten rural housewives selected at random in the area had to cook, in their own homes with a technician present, 3 kilogrammes of beans (a mixture of local varieties) according to three different methods: traditionally, with soaking, and with the haybasket. Only the basic elements of the haybasket were provided, and the housewife assembled It herself. The weight of wood used for each method was noted, as were the cooking time and the activities of the housewife. The latter evaluated the taste, colour, swelling properties, cooking time, wood consumption and general preference for each treatment. When all treatments were finished, we called a meeting of participating housewives to discuss the trials together.[top] [end]Summary of results: 40% Economy of woodThe housewives used on average 6.9 kg of wood for a traditional cooking, but only 4.2 kg using the haybasket: an economy of about 40%. The beans cooked in the basket tasted as good or better than those cooked traditionally. Most of the women wanted to continue using the haybasket. The advantages cited were: time saved (one can leave the house during cooking, instead of tending the fire), wood saved, and a good flavour. The only disadvantage mentioned was the extra time needed for the beans to finish cooking, a nuisance if one was hungry!Soaking, on the other hand, was very unpopular, due particularly to changes in taste and colour of the beans. [top] [end]Follow-up SurveyEleven families (8 out of the 10 in this trial, plus 3 from a previous trial) agreed to continue using the haybaskets. They were visited each week for two months to find out whether they were still using the basket, and if there were any problems. The main problem soon became lack of beans due to a poor harvest! Six months after the first trials they were visited again. Only one had definitely abandoned the method. Of the remaining nine questioned, 4 said that, given a normal supply of beans, they would use the basket all the time; and 3 that they would use it most of the time.The urban housewives using the haybasket are similarly enthusiastic. One household which spent 1800 FRW* per month on charcoal before using a basket, now spends 1200 FRW per month. Another woman has a neighbour who borrows the basket to cook beans overnight, while she uses it in the daytime. * 130 FRW = £1 [top] [end]What next?The technology, simple and cheap, is ready to diffuse on a wider scale. We hope to use existing channels and programmes as much as possible. The Ministry of Energy and several projects are interested. Once a comprehensive instruction booklet is printed, nutrition centres, women's groups and various other missions and projects will be able to propose this technique to a wider public.
[top] [end]Reference(1) 'Elements de Politique d'Economie du Combustible au Rwanda', J.J. Bellamy Association Bois de Feu/GRET, Paris June 1984[top] [end]Contents: Boiling Point 14: Kitchens, Pots and Cooking Practices
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12 September 2008; Last edited:
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