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The Development of an Energy Efficient Electric Mitad for Baking Injeras in

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 75 2017 Proceedings of the 25th Domestic Use of Energy Conference

The Development of an Energy Efficient Electric Mitad for

Baking Injeras in Ethiopia
Robin Jones, Jan Carel Diehl, Leon Simons and Martin Verwaal

e    
Abstract— Preparation of Injera, the cultural staple bread food
item in Ethiopia, is known for its intensive energy consuming
cooking. Baking this food item in the traditional three stone stoves,
with an efficiency of 5-15%, consumes huge amounts of firewood
and causes consequent problems like deforestation, global warming
and household air pollution. Electrical injera stoves (mitads) are a
sound alternative in Ethiopia because of the relatively wide Fig. 1. Injeras and their peculiar texture.
availability of electricity (hydropower). However, these electrical
Mitad have designs dating back to the 1960’s and are highly
inefficient as well and are overloading the electricity grid.
Preparation of injera is known for its intensive energy
Consequently, a research and design project called ‘Magic Mitad’ and time consuming cooking. Baking this food item in the
was initiated to develop an energy-efficient electric injera mitad. traditional three stone stoves consumes huge amounts of
Starting with the introduction of a new type of fuel-efficient baking firewood (95% of the population of Ethiopia still relies on
plate a range of research and design experiments were initiated to traditional biomass fuels for cooking) and this leads in
further optimize the energy-efficiency as well as the baking quality different localities to alarming deforestation of trees, and
of the Magic Mitad. In the first experiment the ‘start-up energy’ of
different baking plates was tested in order to identify and select the
exposing the environment to global warming due to its
most energy efficient one. During the next experiment, the chosen inefficiency [3-5]. In addition, the kitchen environment is
type of baking plate was used for baking injeras to study the heat highly polluted with soot and smoke that affect the health of
distribution. A uniform heat distribution is key to produce high household inhabitants [6].
quality injeras. From the result obtained it was concluded that a Over 90% of energy consumed in household level in
different type of heating element was needed. Ten types of Ethiopia is for cooking and from this injera baking accounts
alternative heating elements were selected of which four were
for 50-75% [3, 7]. Both traditional and newly developed
tested in a lab-setting. Ribbon wire heating element was selected,
and optimized in its lay-out. Finally, the prototypes were tested in biomass injera stoves are energy inefficient [6]. Some
Addis Ababa on quality performance and energy-efficiency researchers indicated that the traditional clay stoves have an
compared to electrical clay mitads. The outcomes were successful estimated efficiency of 5-15% [2, 8-10]. Others show that
in the sense of quality and increased efficiency by 30%. improved biomass stoves, have registered efficiencies in the
range of 25-35% [2, 11].
Index Terms— Clean Cooking, Ethiopia, Heat Distribution,
Energy Efficiency, Injera, Kitchen Environment To mitigate the above challenges, different scholars have
attempted to design and develop injera baking alternatives
1 INTRODUCTION like for example stoves based on biogas, solar power, and
electricity [2, 4, 7, 12]. Because of the relative wide
Injera is the cultural staple bread food item in Ethiopia
availability of electricity in Ethiopia (hydropower),
and made from indigenous grain called ‘teff’. Traditionally,
electricity based mitads are a sound alternative and have
this 60 cm diameter sourdough pancake is baked on a 20–30
become a popular alternative especially in the urban areas.
mm thick clay griddle, called ‘mitad’, placed on three stones
There are currently an estimated 530.000 injera electric
above open fire [1, 2]. Fermented dough is poured on a hot
baking stoves, or alternatively called ‘electric mitads’ in use
clay pan and stays until the boiling temperature is reached;
in Ethiopia [13]. It is estimated that the power consumed by
consequently bubbles from the boiling water escape forming
existing electric mitads (3.5-6 kW per cooker) consume
thousands of tiny craters (eyes) that give the peculiar injera
approximately 60–70% of the Ethiopian hydro-based grid-
texture (see Fig. 1) [2].
power. The daily baking’s power load becomes coincident
with peak load requirements, thereby overloading the
electricity distribution system [13, 14]. The impact is
especially severe on week days, given the timing of Mitad
use—mid morning and mid noon-[14]. Consequently, the
This work was supported in part by the Climate KIC.
R. Jones, Delft University of Technology, Landbergstraat 15, Delft, The current electric mitads in use solve part of the problem, but
Netherlands (robinjones01@gmail.com). meanwhile create new ones as well.
J.C. Diehl, Delft University of Technology, Landbergstraat 15, Delft, The mitad design, in current use, dates back to 1960’s
The Netherlands (j.c.diehl@tudelft.nl).
L. Simons, Magic Ventures, Meentweg 115, 3755 PD Eemnes, The when electric baking of Injera started with high-income
Netheralnds (leon.simons@magicmitad.org). groups in cities[13]. However, since then, almost no design
M. Verwaal, Delft University of Technology, Landbergstraat 15, Delft, improvements have taken place and are highly energy
The Netherlands (m.verwaal@tudelft.nl).
inefficient, given poor design and use practices [14].
 2017 Proceedings of the 25th Domestic Use of Energy Conference 76

Fig. 3. Electrical mitad with clay plate (left) and electric mitad
with MM-plate (right).

Fig. 2. Schematic overview of the components of an electric mitad Typical positive characteristics of the first prototypes
[15]. were shorter heating time, reduction of the required baking
temperature while retaining the baking time of 3 minutes
Sood [14] summarizes the main shortfalls of existing (and shorter reheat time). There were however problems
designs of electric mitads as: with (consistently) baking high quality injeras on the magic
i. The high resistance, inadequately sized electric wiring, mitad plate: slight differences were formed on the eyes
and incorrectly adjusted heating element; (holes) on the injera’s surface. This was due to a non-
ii. Use of poor construction materials; uniform distribution of heat throughout the baking pan.
iii. Poor insulation: dissipation of energy during the baking 2.2 Research and Design Brief
session is said to roughly range 
from 40 to 50 percent;
Hence this project aimed to design, optimize and
iv. Lack of temperature control device such as a thermostat, configure an electrical injera backing stove to enhance its
encouraging loss of heat; and performance. The gap observed in the previous designs was;
v. Overall, sub-optimal/poor and inefficient design and heat transfer and uniform heat distribution through the stove,
workmanship. as well as quality performance. At the start both the energy
All facts mentioned above in this introduction have been efficiency of an electric mitad as well as the quality
motivations to start our research by design project initiated parameters of an injera were defined.
by the start-up company Magic Ventures with the aim to 2.3 Energy Efficiency
develop a more energy efficient electric mitad.
The efficiency of an electric mitad is measured by the
2 RESEARCH & DESIGN CHALLENGE energy [kWh] used per injera in a baking session. This has
2.1 Magic Mitad been defined with the following formula:
𝐸𝐸!"#$"%&
Magic Ventures is a Dutch Start-up which develops 𝐸𝐸!"#$%& = 𝑃𝑃 ∗ 𝑡𝑡 +
𝑁𝑁
products and services that utilise (western) developed
technology to create energy-efficient products with high 𝐸𝐸!"#$%& = 𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸  𝑝𝑝𝑝𝑝𝑝𝑝  𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖   𝑘𝑘𝑘𝑘ℎ
quality and performance for developing areas. At the start of
𝑃𝑃 = 𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀  𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃   𝑘𝑘𝑘𝑘
this research project, the company was working on a proof
𝑡𝑡 = 𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏  𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐  𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡  𝑝𝑝𝑝𝑝𝑝𝑝  𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖   ℎ
of concept of a new electric mitad to reduce energy needs of
𝐸𝐸!"#$"%& = 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆  𝑢𝑢𝑢𝑢  𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒   𝑘𝑘𝑊𝑊ℎ
baking injera, by introducing a fuel-efficient baking plate.
This was done under the project name “Magic Mitad”. The 𝑁𝑁 = 𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴  𝑜𝑜𝑜𝑜  𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖  𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏  𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑  𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠
aim was to further improve the energy-efficiency of this new 2.4 Quality of injera
type of electric mitads while keeping the quality of the It is essential for the user acceptance of a new energy
baked injeras equal to traditional biomass fuelled stoves. efficient electric mitad that the injeras are of the same
Current electric mitads use a traditional clay baking quality as those baked on the traditional clay mitads. Based
plate, but with grooves cut in the underside, in which the on literature and observations in the field, it was determined
heating element is embedded. As heating element, a coil- that the following characteristics define a good quality
shaped resistance wire in a lay-out consisting of concentric injera:
rings is used. The first prototype at the start of the Magic Subjective:
Mitad project used the same type of heating element but -­‐ “Eyes” on top side
placed a few centimetres underneath a glass sheet (instead of -­‐ Smooth underside
embedded in a clay plate) (See Fig. 3). Prior research and -­‐ Thin, crispy edges
field tests by the company showed the energy saving Objective: (averages, as baked in Addis Ababa)
potential of glass compared to the traditional clay mitads. -­‐ Diameter: 56 cm
Within this paper we further refer to this new type of baking -­‐ Thickness: 3-5 mm
plate as ‘MM-plate’ (referring to Magic Mitad). -­‐ Weight: 330 g
2.5 Research & Design Experiment Cycles
Since the project did have technical challenges (energy
efficiency) as well as user acceptance challenges (injera
 77 2017 Proceedings of the 25th Domestic Use of Energy Conference

quality) it was decided to combine technical lab experiments Results

with design experiments in the field (Ethiopia). The project The horizontal axis in Fig 5 shows the time while the
existed of in total six sequential experiment cycles which vertical axis shows the temperature. The X marks the time at
will be described the following sections. which the power was switched off for each test. The MM
3 RESEARCH & DESIGN EXPERIMENTS baking plate reaches 250°C after eight and a half minutes,
while the clay baking plate takes 35 and a half minutes.
3.1 Experiment 1 Efficiency: Start-up Energy
The start-up energy is one part of the efficiency formula
(see 2.3) which could already be tested in a lab stetting at
Delft University of Technology. Start-up energy is used to
heat up the mitad, as a preparation for baking the injera. The
heat contained by the mitad is usually lost to the
surroundings at the end of the baking session. The start-up
time is also an indicator for the reheat time in between the
baking of each injera (especially relevant in bakeries).
To quantify the start-up energy a heating-up test was
conducted, the expected results were temperature curves
Fig. 5. Mitad heat up characterization: Temperature [°C] over time
(over time) of MM baking plates and clay baking plates. The [h:mm:ss]
results of this experiment indicated to what extent the start-
up energy of a mitad has an influence on the overall baking The power for both tests was the same (2,55 kW). As
efficiency. such the ‘start-up energy’ indicated in kWh is determined by
𝐸𝐸!"#$"%& the heating up time. The start-up energy for the MM plate
𝐸𝐸!"#$%& = 𝑃𝑃 ∗ 𝑡𝑡 +
𝑁𝑁 was 0,35 kWh versus 1,48 kWh for the clay plate.
The start-up energy is divided over the total amount of
injeras baked in a session. If proven to be significant, the Conclusions
start-up energy is especially important when few injeras are The MM plate has a significantly shorter start-up time
baked in a session, as is the case for households. Since the and therefore requires less start-up energy compared to the
start-up energy is also an indicator for the reheat energy (in traditional clay baking plate. This indicates that the reheat
between baking each injera), it is also an indicator for the time in between the baking of each injera will also be
overall efficiency of large sessions, as is the case for B2B shorter for MM compared to clay. The results of this
scenarios (i.e. injera bakeries). experiment support the earlier findings which indicated that
the MM plate may have a significantly higher energy
Methods efficiency than clay. This led to the decision to continue the
To quantify the ‘start-up energy’ of a mitad with MM further development with the MM plate.
plate compared to one with a clay plate, a heating-up test
was conducted. This test consisted of measuring the required 3.2 Experiment 2 Quality: Baking tests
amounts of time and energy to heat up the clay and MM Even though the MM plate proved to be a promising
baking plates to baking temperature (250°C). A MM baking direction for energy efficiency compared to the clay plate, it
plate and a traditional clay baking plate were mounted on was not yet possible to bake injeras with consistent quality
the same heating element and heated up. Temperature was on the MM plate. It was suspected that a non-uniform heat
measured with both a thermal imaging camera and an IR distribution might be the cause of the baking quality
thermometer. Power and energy consumption were problems. In order to investigate the non-uniformity of heat
measured with a power and energy meter, which also distribution baking tests were performed to validate this
functioned as a timer (see Fig. 4). assumption as well as to discover other potential causes of
baking problems.
Some of the thermal properties of glass (MM plate), like
specific heat capacity, are similar to those of Ethiopian clay
(See Table 1). Other properties like thermal conductivity are
different, which have an influence on the heat distribution.
The low thermal conductivity and thickness of the clay plate
make it in fact an insulator, allowing the heat to evenly
spread across the baking surface. The MM plate is thinner
and transfers the heat faster, causing an unevenly heated
baking surface.

Fig. 4. Schematic overview of the experiment setup.

 2017 Proceedings of the 25th Domestic Use of Energy Conference 78

Table I: Specific material characteristics of Ethiopian presumed cause of the injera burning and sticking to the
clay and glass. mitad. A different type of heating element is required to
Property Ethiopian Glass achieve a satisfactory heat distribution.
Clay The Magic Mitad V1 prototype has a power rating of
Thermal Conductivity [W/mK] 0,34 1-1,4 about 2,55 kW. The baking test showed that this is too
Specific Heat Capacity [KJ/kgK] 0,83 0,84 much, the baking plate often became too hot, causing the
injera to burn. To gain more control over temperature and
Methods heat transfer, a power control unit was installed, allowing
Two professional Eritrean chefs prepared teff-based any power level between 0 and full power. By baking at
injera dough (as used in Ethiopia). Six injeras were baked on various temperatures and power settings, ideal values can be
the Magic Mitad V1 prototype. The test consisted of the determined for baking on the MM baking plate.
following quality evaluation steps: 3.3 Experiment 3 Efficiency: Heating element
i. Subjective evaluation of baking quality (by professional In order to overcome the non-uniform heat distribution,
chefs); alternative heating elements were being explored. After an
ii. Measurement of the heat distribution on the mm baking initial exploration ten types of heating elements were further
plate (without injera). evaluated and a selection was made based on criteria such as
power per area, energy efficiency and price (see Fig. 8).
The heat distribution was measured with a SP These heating element were evaluated on a number of
Thermoview 8300+ infrared thermal imaging camera with a criteria, which are based on the preliminary requirements.
480 x 640 resolution micro-bolometer. For the first set of criteria the alternatives were evaluated on
a pass or fail basis:
Results • Able to reach and maintain a temperature of at least
The tests led to the following two main results: 220°C.
i. It was not possible to achieve satisfactory baking quality. • Acceptable heat distribution (less than 20°C
The injeras did not have a smooth underside since they temperature differences across the baking area).
kept sticking or burning to the mitad. The professional • The output power should be close to 1,2W/cm2.
chefs evaluated the baking quality as being
unsatisfactory. For a second set of criteria the alternatives were judged
ii. Heat distribution measurements: the Magic Mitad on their performance relative to the other alternatives:
prototype recorded temperature differences of over • Price.
40°C (see Fig. 7). The heat distribution was non- • Efficiency (also: conduction versus radiation and
uniform. convection).
• Possibility of local production.

This resulted in four remaining types of heating

elements, which could be suitable for the Magic Mitad. This
included the original coil wire, which might still give
satisfactory results when placed in a different layout or
when installed in an altered way. In addition the ribbon
wire, silicon heater, and micanite heater were selected.

Fig. 7. MM mitad with coil wire element: temperature differences

>40°C. The graph shows temperature (vertical axis) along section
line L1 (horizontal axis).

Conclusions
It was determined that the unsatisfactory baking results
of the Magic Mitad are strongly related to:
• Uneven heat distribution;
• Incorrect baking temperature / heat transfer.

To form a smooth under layer, it is essential that the

mitad reaches the right temperatures and that the proper
amount of energy is transferred throughout the baking
process. The heat distribution is directly related to this. A
Fig. 8. Exploration, evaluation and selection of alternative heating
non-uniform heat distribution means that some places of the
elements [15].
baking surface will have an incorrect temperature and
energy supply. The temperature differences of >40°C are the
 79 2017 Proceedings of the 25th Domestic Use of Energy Conference

Methods Table III. The coil and ribbon wire and their respective heat
The test setup for Experiment 3 was the same as for distribution as recorded by the IR camera.
Experiment 1. For each test one of the four selected heating Wire type Wire Heat distribution
elements was mounted underneath the MM plate of the with MM plate
Magic Mitad prototype. The measurements during each test Coil wire
include heat distribution and start-up time.
The first two tests were done with ready-made heating
elements:
• Silicon heater (resistance wires insulated by silicon);
• Micanite heater (resistance wires insulated by
micanite). Ribbon wire
The last two tests were with two resistance wires,
without a layout, only a single wire:
• Coil wire (as used in current electrical mitads and in the
Magic Mitad V1 prototype);
• Ribbon wire (as used in modern electrical cooking stove
tops).
The graph below in Fig. 9 shows the heat distribution
Results
across Line 1 for both the coil wire (blue) and ribbon wire
The silicone heating element provides a relatively even
(red) after ten minutes of heating. The graph shows that
heat distribution on the MM baking plate (see Table II). It
across the same distance, the ribbon wire has a more
does have a relative long start-up time: 12 minutes to reach
distributed curve. Also, within the same time it heats faster,
162°C. The element has a relatively high efficiency because
and it has a higher power density.
of direct conduction to the mm plate (instead of radiation
and convection), however the power per area remains too
low.
During heating up, the micanite heating element
deformed significantly and started to touch the MM plate at
some places, which caused local hotspots (see Table II).
Besides these hotspots, the element caused a major cold spot
above the hole in the centre of the element. The micanite
heating element did have a fast start-up time: 1 minute to
reach 173°C.

Table II: The silicon and micanite heating elements and their
respective heat distribution as recorded by the IR camera.
Heat element Element Heat distribution Fig. 9. Thermal image Graph with heat distribution across Line 1:
type with MM plate coil wire (blue) and ribbon wire (red).
Silicon
Conclusions
The start-up time of the silicon heating element is too
long and its power per area too low. Perceived advantages
such as more direct energy transfer trough conduction
proved to be insufficient.
After contacting several manufacturers, it became clear
that the micanite element will always have unheated parts on
its surface. This will cause major temperature differences
Micanite which also makes it unsuitable for the Magic Mitad.
The ribbon wire showed better results compared to the
coil wire in terms of heat distribution and start-up time and
was therefore selected for further development. The better
heat distribution can probably be explained by the more
vertical geometry of the ribbon wire compared to the coil
wire. The surface area of the coil wire is at a 90° angle with
the surface of the mm plate, therefore it is likely to spread
the heat further than the coil wire.
In terms of production, the ribbon wire can be placed
Isolated sections of the ribbon and coil wire were
compared to each other as well. The ribbon wire shows a much more precisely on the element bed than a coil wire.
More accurate wire placement will be beneficial to the
faster start-up time and a greater and more even heat
overall uniformity of the heat distribution.
distribution compared to the coil wire (see Table III).
 2017 Proceedings of the 25th Domestic Use of Energy Conference 80

The next step is to develop a wire layout which provides The third concept (right) has the lowest amount and size
a satisfactory heat distribution. of hot-and coldspots (and consequently the most uniform
heat distribution) and was therefore selected.
3.4 Experiment 4 Quality: Wire layout optimization
As an alternative for the coil wire, the more suitable Method 2:
ribbon wire was identified with a more uniform heat To validate and improve the spiral layout concept, in
distribution and faster start-up time. Part of the problem iterations, nine prototypes were made using a ribbon wire
with the old element was the wire layout. The new ribbon from a kitchen stove element. First a prototype was made
wire allows more accurate placement, by which it should be without the use of any template. In case the results proved
possible to achieve a uniform heat distribution with an unsatisfactory, first a hand-cut cardboard template was used
optimized layout. Several layout concepts have been to position the wire. For even more accurate wire placement
evaluated with quick simulations. The best layout concept a laser-cut MDF template was used for the 7th iteration. A
has been further developed by prototyping and further double spiral design was implemented so that the wire
optimization with computer simulations. would start and end at the edge of the element (instead of
ending in the centre), a requirement for production (see Fig.
Methods 11).
Several wire layouts were explored. They were evaluated
using three methods:
i. Simulation with Adobe Photoshop “glow effect”
function;
ii. Making a physical prototype and measuring heat
distribution with thermal camera;
iii. Simulation with SolidWorks thermal simulation. Fig. 11. Several prototype iterations of the chosen spiral concept.

Method 3:
The first method was used to quickly evaluate different
The double spiral prototype still had two cold spots in
layout concepts. The second method was used to more
the centre. Another prototype was made (8th iteration) with
accurately evaluate different iterations of the chosen layout.
less space between the wires in the centre, but the problems
The third method was used as an optimization step to
remained. A SolidWorks simulation was performed to
eliminate hot and cold spots in the centre.
optimize the centre of the layout without having to prototype
each iteration (see Fig. 12).
Results
Method 1:
A line was drawn in Photoshop, to which the “Outer
Glow” effect was applied (see Fig. 10). The contour of the
glow was chosen to match the heat distribution graph of the
ribbon wire in Experiment 3. Three layout concepts were
made in this way. Whenever a line has a sharp bend, a
hotspot appears.

Fig. 12. A SolidWorks simulation result of the 8th layout iteration

(left) compared to a thermal image of the physical prototype of the
8th layout iteration (right).

After optimization in SolidWorks, a 9th and last

prototype iteration was made. This prototype provided
Fig. 10. Three layout concepts: the spiral concept shows the most satisfactory results in terms of heat distribution. Apart from
uniform heat distribution without hotspots. the edges, temperature differences are <20°C (see Fig. 13).

The spiral shape layout (right) was selected from three

different concepts. The selection was made based on the
amount and size of hotspots:
• The first concept (left) has 8 hotspots and several
coldspots along the side.
• The second concept (middle) has 6 hotspots and 4
coldspots.
• The third concept (right) has no hotspots, only two
coldspots. It is suspected that the layout in the center
can be optimized to remove the coldspot in the center. Fig. 13. Temperature distribution of the Magic Mitad prototype
with enhanced ribbon wire heating element with optimized layout.
The graph shows temperature (vertical axis) along section line L1
(horizontal axis).
 81 2017 Proceedings of the 25th Domestic Use of Energy Conference

Conclusions
After exploring three different layout concepts, the spiral Table IV: Baking time, energy consumption, and energy savings.
layout was selected and further optimized. Challenges with Mitad type Baking Energy per Energy
the spiral layout include the edges and the centre. After nine cycle time kg injera savings
iterations, a layout was conceived with an acceptable (m:ss)
uniform heat distribution. The new heating element was Traditional clay 4:15 658 Wh -
evaluated with another baking test, which showed very mitad
promising results. The next step was to validate the Improved Magic 3:00 460 Wh 30%
improved design with field tests. Mitad
3.5 Experiment 5 Quality: Baking test in the field.
After selecting the proper heating element as well as Concerning injera quality: both the objective and
optimizing the layout of the heating element it was time to subjective evaluations were mostly positive, the Magic
go to Ethiopia to test in the field the energy efficiency and Mitad injeras were almost indistinguishable from clay mitad
baking performance of the improved Magic Mitad. injeras in terms of thickness, “eyes” on the top side and a
smooth under layer. The main point of improvement
Methods concerned the edges, which were not thin and crispy like on
Based on the Controlled Cooking Test [16], the mitad the clay mitad injeras.
efficiencies were evaluated by measuring the energy
consumption per kilogram of cooked food. At the test site, Conclusions
Addis Ababa University Bakery, about 150 injeras are baked The combination of the new heating element with the
each day, seven days per week. Baking in such large MM baking plate can result into 30% energy savings.
quantities made it possible to more accurately evaluate Injera quality was positively evaluated by experts, except
efficiency and other aspects such as usability. for the edges. It is assumed that the edge problem can be
solved by changing the geometry of the MM baking plate.
i. First the quality of the injeras baked on the Magic Mitad
were evaluated in two ways. First by comparing them to 3.6 Experiment 6 Quality: Power settings
the injeras baked on clay mitads and evaluating the The currently used electrical clay mitads only have two
desired injera properties as stated in section 2.4. power setting: on and off. During baking the power is
Secondly the injeras were subjectively evaluated by
always on, the power level is chosen in a way that enough
interviews with professional injera bakers (working at
energy is supplied during the baking process. The power
bakeries), chefs and other locals. The injeras, which
level is also one of the determinants of the baking cycle
were baked that same day were shown to the
interviewees. Questions asked included: “What is your time: how long it takes to reheat between baking of injeras.
opinion of the quality of these injeras?”. The purpose of this experiment is to determine this power
level for the Magic Mitad, to allow continuous baking
ii. Next the energy efficiency of current electrical clay
mitads as well as of the new improved Magic Mitad was without having to adjust the power.
measured. The efficiency was calculated using the
formula as presented in 2.3. For this purpose the Methods
following measurements were made: During baking, the power level was adjusted to several
different levels with a power control unit, ranging from
• Power was recorded with a power- and energy meter.
2000-2600W, in order to compare baking quality.
This device measures the amount of power [kW] drawn
The baking temperature was determined by the
by the mitad, this amount is relatively stable over the
experienced professional chef. When the chef deemed the
duration of the baking session.
temperature to be correct, she poured the dough onto the
• Baking cycle time was recorded with a timer / stopwatch
mitad. Methods for evaluating temperature (by the chefs)
device.
include:
• Startup energy was recorded with a power- and energy
• Spreading ground up oily seeds (mushit) on the baking
meter. This device measures the energy consumption
area and evaluating the colour change (from brown-
[kWh] during the heating up process.
yellowish to dark brown) and smoke;
• (amount of injera’s baked during a session)
• Pouring a few drops of dough onto the baking area and
judging by visual and audible feedback.
Results
The results show that the Magic Mitad configuration has
Results
a higher efficiency than the clay mitads. The ‘magic mitad’
The highest quality baking results were achieved with a
showed the highest efficiency: up to 30% energy savings
continuous power level of 2000W on a 48,5cm diameter
compared to the current electrical clay mitads.
baking area (1,09W/cm2).

Conclusions
After further optimization the baking area was increased
to 54cm diameter, which corresponds to a power setting of
2500W (1,09W/cm2).
 2017 Proceedings of the 25th Domestic Use of Energy Conference 82

4 CONCLUSIONS AND DISCUSSION [12] Tafere, A.T., Experimental inverstugation on performace

characteristics and efficiency of electric injera baking pans (‘Mitad’),
Electricity based mitads are a sound alternative for the in Energy Technology. 2011, Addis Ababa University: Addis Ababa.
energy inefficient traditional three stone fire mitad ovens. [13] DANAS, Project Document on Electric Injera Mitad: Energy
Efficiency Standards & Labeling. 2015.
However, also their energy efficiency has to be improved [14] Sood, D., Injera Electric Baking: Energy Use Impacts In Addis Ababa
drastically in order to prevent an overload on the electricity Ethiopia, W.B.A. Region, Editor. 2010, World Bank Africa Region:
grid. Washinghton.
[15] Jones, R., Magic Mitad: Development of Energy Efficient Injera
The Magic Mitad project as discussed in this paper has
Stove for the Ethiopian Market, in Industrial Design Engineering.
resulted through a range of research and design experiments 2015, Delft University of Technology: Delft.
in a new type of electrical Mitad. The most recent version of [16] Bailis, R., Controlled Cooking Test (CCT). 2004, Shell Foundation.
the Magic Mitad prototype has some significant advantages
as well as disadvantages compared to the electrical clay
mitads. The energy efficiency of the Magic Mitad is AUTHORS BIOS AND PHOTOGRAPHS
significantly higher compared to the electrical clay mitads
(up to 45% higher). The quality of the injeras baked on the
Magic Mitad was perceived by experts as very high, Robin Jones received his MSc degree in
comparable to the quality of injeras baked on clay mitads. Integrated Product Design from Delft
University of Technology in 2015. At Delft
Good uniform heat distribution has proven to be the key to a
University of Technology he took an interest in
quality injera and as such key to user acceptance. sustainable design as well as medical design.
A disadvantage of the Magic Mitad is the expected retail Currently pursuing entrepreneurial ventures
price, which is higher than for a clay mitad. This makes the with a start-up in the YES!Delft tech incubator
Magic Mitad unaffordable for low-income households, since focussing on 3D scanning and printing for
energy savings (in the context of Ethiopia) do not customized orthotics..
compensate for the high initial investment. In the setting of a
bakery with up to 16 hours of baking each day, electricity Jan Carel Diehl received his MSc and PhD
costs do become very significant. Savings on electricity degrees in Industrial Design Engineering from
could compensate for the initial investment of purchase Delft University of Technology. In his present
within a few months. Also, since the baking time is up to position, he is assistant professor for the Design
37% faster, this means that fewer mitads are required to for Sustainability (DfS) research program and
bake the same amount of injeras each day. senior researcher within the Delft Global
The Magic Mitad is in ongoing development, with the Initiative and the LDE Center for Frugal
Innovation in Africa.
aim to find a balance between efficiency, baking quality and
cost price. Other factors such as local production and .
durability also play an important part. Presenting author: The paper will be presented by Jan Carel Diehl
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