| Boiling Point No. 10 - August 1986 |
By: Frans Sulilatu
A contribution of the Woodburning Stove Group, The Netherlands
Ouagadougou with about 600 breweries and an annual beer production of 35 million litres, is one of the largest beer consumers in Burkina Faso. The consumption of this popular so-called Dolo beer is estimated to be 250 litres per head of the population annually (whilst in the Netherlands it stands at 85 litres of factory beer per head annually in total). It has also been estimated that about 20% of the total annual wood consumption in Ouagadougou is used to provide energy for the production of this locally brewed beer.
In the light of the foregoing, the German organisation - GTZ, (Deutsche Gesellschaft fur Technische Zusammenarbeit) requested the Woodburning Stove Group to carry out a mission of two months duration in Burkina Faso in order to investigate the possibility of reducing wood consumption of dolo beer cookers. The mission was carried out in co-operation with L'Institut Burkinabe de L'Energie, Ouagadougou.
The Dolo Process
Dolo beer is an aerated alcoholic beverage, prepared from Sorghum grain, water and yeast. Sorghum is used because of its high starch content.
Dolo beer brewing is a domestic affair and just as with all food preparation or processing tasks in Burkina Faso, it is a matter for the women, the so-called Dolotieres.
The process can be divided into three phases:
Malting is conversion of sorghum into malt through germination of the grains. During germination, liberation of the starch in the Sorghum grain is initiated and starch fission products (enzymes) are formed.
First of all, the germinated sorghum is ground into a coarse flour followed by the preparation of the mash by adding water and a gelatinous substance (sap of the yolgha or gombo bark) to the flour. The latter is done in order to avoid curdling. After some hours, the top layer, already containing soluble sugars, is skimmed off to separate it from the mash.
Next the remaining part of the mash, mainly containing starch, is heated. During this process the starch is converted into dextrine and a part of the dextrine into maltose.
Following hereon, the liquid is mixed with the earlier decanted liquid. The mixture is now cooled down during a certain period of time (continuation of saccharification).
After filtrat on of the liquid so produced, the second cooking period starts with the object of concentrating the unfermented dolo by evaporating the surplus water. In consequence, the sugar content, finally determining the alcohol percentage of the Dolo beer, increases.
After a cooling period, yeast is added and the conversion of the sugar into alcohol starts. From now the dolo beer is ready for consumption. Dependent on the customer's alcoholic needs, the beer can be consumed right away or at the end of the fermentation process. Generally in Burkina Faso, the alcohol percentage of Dolo beer will not exceed 6%.
The characteristic features of the brewing process are the two cooking periods. Average cooking periods of 4 and 12 hours respectively were observed at the Dolotieres visited in Ouagadougou. The duration of the total brewing process is about 44 hours.
At the present time Dolo beer has to compete on the market with beer brewed in factories such as those of SO.B.BRA and BRIKANA in Ouagadougou and Bobo Diolaso.
However it is expected that the Dolo beer will stand the competition because of its immense popularity arising mainly from its social significance for the Burkinabe.
The most common of the traditional dolo cookers in Ouagadougou are the regrouped cookers (77%) and the line cookers (22.7 %).
* The regrouped-cooker comprises a number of earthenware jars each of which is supported in the centre and all of which are arranged to form a square (see fig. 1).
The combustion chamber is located in the centre of the square so formed. Each jar contains 80 litres of dolo beer in preparation, thus 320 litres of the brew can be cooked at a time.
The total production however may well be in the order of 700 litres, which implies that preparation is then carried out in two batches. The cooking efficiency of this type of dolo cooker is 17%, with a power output of 80 Kw.
* The line cooker comprises number of earthenware jars or aluminium pots which are generally lined up against a wall in such. a manner that each can be fired separately (fig. 2). The particular one visited was equipped with nine No. 40 aluminium jars, the price of each one of which is about 10 times that of the earthenware jar.
The total production from one dolo preparation at this particular brewery was 900 litres at a time.
The cooking efficiency of the line-cooker is 15% with a power output of about 35 Kw.
The low efficiencies of the regrouped-cookers can be attributed to the poor heat transfer to the jars due to the unfavourable position of the jar-supports.
The low efficiencies of the line-cooker on the other hand can be attributed to the enormous heat losses due to radiation and convection at the wood-fuel entrances.
The foregoing comments apply to the breweries visited in Ouagadougou only.
The price of each of the stoves is mainly determined by the type of brewing-pot used rather than by constructional material costs (generally banco and rock waste).
Improved Dolo Cookers
The designs of the-improved dolo cookers were: based on-the resuIts of several visits to the breweries and on interviews with some of the Dolotieres. An important consideration was the cost of the new designs. It has been stated that these should not exceed the costs of the traditional cookers.
It is conceivable that a Dolotiere has no motivation to buy an expensive cooker of improved design with a long pay-back time for her investment when she already makes high profits with her traditional cooker.
Other important matters taken into consideration were:
* improvement of the heat transfer to the jars
* extension of the working-life of the earthenware jars
* the possibility of continuing brewing in the event of one of the earthenware jars being cracked.
* the attractiveness of improved cookers
Although it had been expected that cookers equipped with aluminium jars would save more wood, considerable attention was given to cookers equipped with earthenware jars. The reason for this was the fact that many Dolo consumers had an aversion to Dolo brewed in aluminium jars. A probable explanation for this is that the taste of Dolo is affected by brewing in aluminium pots.
Three improved cookers have been designed constructed and tested. They are the so-called BURKIDO 1, the BURKIDO 2 and the FOYER SEUL. The designs of the Burkido land 2 are based on that of the traditional regrouped cooker.- The two models are the same in principle, however the jars of the Burkido 2 are sunk deeper into the cooker. This particularly applies when aluminium jars are used becaused they need not be replaced as often as earthenware jars.
As opposed to the design of the traditional regrouped-cookers the Burkidos are provided with two combustion chambers (see fig. 3). The construction materials used are banco and rock waste. -
A considerable improvement in the heat transfer is obtained by providing better supporting means for the jars. The working-life of earthenware jars will also be extended through a better distribution of the thermal load.
The advantage of having two combustion chambers lies in the fact that Dolo brewing can continue during maintenance of a part of the cooker or during relacement of broken jars. Yet another advantage is that better control of the fire can be achieved.
The improved Foyer Seul type of cooker is made for preparing small quantities of Dolo beer and is constructed to accommodate a No. 20 aluminium pot. The cooking efficiency is 40%.
The foregoing quoted cookers were designed in accordance with the design rules generally in use with the Woodburning Stove Group.
Neither the Burkido l and 2 nor the improved Foyer Seal are provided with a chimney or a grate.
The efficiencies for both the traditional cookers and the improved cookers are in figure 3.
The efficiency of the earthenware jar equipped Burkido 1 is 34% and the efficiency of the aluminium-pot equipped Burkido 2 is 53%. When compared with the traditional cookers, theoretical fuel savings of 50% and 65% respectively could be achieved.
The costs involved in purchasing an improved dolo cooker mainly depend on the choice of, or preference for, either an earthenware jar or an aluminium pot. Assuming now that a dolotiere prefers to use her old earthenware jars, then the labour costs involved in building the cooker will be the only expense. The pay-back time is estimated to be in the order of one week.
A changeover to aluminium pots means a considerable investment for the Dolotiere and in such a case the pay-back time is estimated to be in the order of 3.5 weeks. The calculations were based on the assumption that the Dolotiere is willing to spend her total profit in buying one of the Burkidos. Furthermore, an assumption was also made that theoretical fuel savings of 50% and 65% respectively could be achieved.
Supposing now that this is not the case and that the fuel savings amount only to 25% and 32% respectively, the pay-back time is expected to be in the order of 6.5 weeks and from this it can be concluded that the price is not the stumbling-block!