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Bread Ovens by E Shirey et al.
The first article starts from ancient Egyptian, Greek and Roman designs, through the middle ages up to modern, continuous process, steam heated ovens which produce the unpleasant and unwholesome food which most people in developed countries now eat. Retained heat type ovens predominated until quite recent times when the more efficient ovens with separate fire boxes were developed. The article illustrates the basic designs of ovens (Fig. 1) and the traditional English types of loaves but it should be recognised that in many Third World countries, 'loaves' are not the traditional forms of bread and may not be preferred. Many of the traditional forms, particularly unleavened and flat bread, need special oven designs. In Iran, which has perhaps the best bread in the world, small bakers specialise in one or two of the 7 or 8 common varieties and have appropriate ovens baking 3 times per 24 hours. By promoting an 'improved' and more fuel efficient oven design, we may be influencing a basic item of diet. Loaves are more convenient but are they better food, better tasting, more suited to the normal diet or do they need imported cereals or flour?
The second paper starts from the statement that traditional ovens make good bread but are inconvenient and use too much fuel for small communal baking. It explains the esentials of the complex chemical processes of baking by which dough is converted into bread. It then looks at three types of stoves: 1) the hole in the ground amd tandouri ovens for flat bread 2) retained heat or "beehive" type, ideal for crusty loaves because baking is mainly by radiant heat. The geometric form of this oven is important for good circulation of the hot air as well for even radiation. The walls should be thick with a high thermal capacity and an outer, insulating layer using suitable local materials. The low thermal efficiency is indicated by the fact that 200 Kg of wall material has to be heated to 300 ºC to bake 50 Kg of bread which only needs a baking temperature of 170 °C. The article goes on to describe a double oil drum oven which has insulated outer walls and a space between the 2 walls for hot gas circulation from the separate firebox. The third paper is a 16 page manual for the construction of such an oven. It lists the materials and quantities needed-and shows the tools and techniques involved in the cutting and jointing. It is the scrap metal and hammer and chisel method used throughout the Third World and shows the construction of the chimney and how it should be passed through the roof of the hut.
The last paper deals with oven testing and evaluation emphasising fuel efficiency but also looking at convenience factors. It recommends the use of "controlled cooking tests" which measure the amount of fuel required to bake a measured amount of bread etc. rather than PHU tests. Oven temperature and efficiency is related to batches of cooking throughout the daily baking cycle. The wide variation in fuel efficiency between different types of ovens (see table) is shown from a Somalia example - a retained heat oven used 6 tonnes of wood to bake 2000 Kg of flour in 30 days (efficiency 0.33 Kg flour per Kg of wood), compared with a large, steam tube oven which used 6 tonnes of wood to bake 37,500 Kg of flour in 3 days (efficiency 6.25), i.e. 20 tonnes more efficient. Details of the test procedure are given so that results could be used for international comparisons see table.
The convenience factors considered are:
The 4 articles provide a very useful introduction for anyone starting to tackle the problems of saving wood or other fuels used in ovens for baking or similar processes. The potential savings are of national significance for most Third World countries and should not be overlooked by their stove projects. ITDG plans to intensify its work in this field and will shortly be making the 4 articles available in a combined form.
[top] [end]Contents: Boiling Point 10: Institutional and Community Stoves
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Page created:
30 September 2008; Last edited:
30 September 2008; Version: 0 | |||||||||||||||||||||||||||||||||||||||
Pagename: BP10:BreadOvens @HEDON: TWNA | |||||||||||||||||||||||||||||||||||||||
