Development and performance evaluation of an improved electric baking oven for baked products

Abstract An improved electric baking oven was designed and fabricated using locally available materials for baking cakes and biscuits. Provisions of necessary adjustments were employed for ensuring uniform distribution of heat in all trays of the baking chamber. Its baking characteristics in terms of baking time, specific volume, and product quality in terms of sensory attributes were evaluated. The oven was found to be quite satisfactory in functioning for baking cakes and biscuits. Total time was only 15–28 min for baking the cake samples in the oven. On the other hand, comparatively, a bit longer time 18–35 min required for baking the biscuit samples. Baking cost was lesser in baking small‐sized cakes and biscuits than those of large sized. The quality of baked products was better in terms of taste, color, flavor, texture, and appearance than ordinary market products. Loaf volume of each cake (with 4 × 5 × 8 cm3) was 100%, which gave specific volume of 652.8 cm3/kg. Similarly, the specific volume of biscuits was 810 cm3/kg. The electric baking oven is quite efficient in baking quality cakes and biscuits uniformly, which can be provided to rural small entrepreneurs for commercial manufacturing of biscuits and cakes.

Ovens have been used since prehistoric times by cultures that lived in Egypt. Hence, before the intervention of modern baking ovens, people had alternative means of cooking and baking. The different types of baking ovens are earth oven, ceramic oven, gas oven, wall oven, and electric oven. By considering their energy source, ovens can be broadly classified into two groups, fuel-based and electric ovens (Mullinger & Jenkings, 2008). Electric resistance heating has various advantages over systems based on fuel combustion, such as increased control accuracy and heating rate. Researchers have analyzed diverse types of ovens (Khatir et al., 2012;Mirade et al., 2004).
Development of a small-scale electric oven for baking quality products is important to create business opportunities for an entrepreneur. The insulator helps in preventing heat loss from the oven and may allow the baking oven to be turned ON and OFF automatically at preset times, and it can also be used to shut the baking oven off when the food is completely cooked or when the cake is completely baked to the desired degree.
Several works have been carried out on baking ovens due to its importance and ease of operation. Genitha et al. (2014) developed a domestic gas oven by which higher energy efficiency was obtained by reducing the energy, cost, and time of baking. Adegbola et al. (2012) developed a low-cost domestic electric baking oven with the incorporation of a blower for improved efficiency. Boulet et al. (2010) designed a bakery pilot oven by CFD modeling. Therdthai et al. (2003) designed an efficient and cheap gas oven by using the software 3D solid works which showed the pictorial views, lines, and dimensions for the fabrication. In the fabrication process, the major design considerations were considered as emphasized by other researchers (Akinnuli & Olufemi, 2019). However, it should be noted that the existing baking oven takes much time because of the long waiting time of the users to have their food ready. Also, the performance of those ovens is very low and not up to standard.
Hence, to improve the performance of the existing oven, there is a need to develop an improved electric baking oven through the incorporation of thermostat and interlock switch. The proposed electric baking oven would be portable, readily available, relatively cheaper, and easy to install and operate including high durability compared to other types of ovens. This oven is also aimed to develop targeting daily local market demand for an area so that small entrepreneurship can be encouraged. The performances of the oven in terms of baking characteristics and quality of baked products have been evaluated.

| Collection of materials
Required materials such as mild steel sheet grade 1, stainless steel sheet grade 1, electric cable, temperature sensor, and conductor were purchased from the local market of Dinajpur. Glass wool insulator (grade 1) and electric heater were purchased from Nowabpur, Dhaka.

| Design procedure of the improved electric baking oven
A comprehensive approach was used for designing and fabricating the baking oven to be used for baking various products. Locally available common materials (mild steel sheet, stainless steel sheet, glass wool, and electric wire) were used for fabricating the oven (Table 1).

| Design consideration
During the development stage of the electric oven, a few important design considerations were taken into consideration to customize the size and volume of the electric oven to make it capable of baking various types of cakes and biscuits such as: 1. The oven can be fabricated in local workshops by local mechanics.
2. It will be energy efficient. It will be compact in size and attractive in shape.
3. The oven can be operated at variable temperatures within 150-250°C.

The fabrication cost is reasonable (<US$200).
5. The loading and unloading system will be manual.
6. Finally, it will be operated by a single-phase electric line for operating in rural areas.

| Selection of construction materials for the oven
The following materials were selected on the basis of the design consideration and requirements for fabrication of the electric baking oven.

| Design of the main structure
The main structure represents the entire outlook of the electric oven ( Table 2). The dimension of housing unit is selected as 60 × 40 × 45 cm (length × width × height) and easy operation to make it attractive in appearance. The housing unit of the electric oven is made of 16-gauge mild steel sheet, which makes the oven stronger and have smooth surface finish. The wall of the housing unit was insulated by glass wool maintaining 25.4 mm (1 inch) on all sides.

| Design of the baking chamber
The baking chamber is an air-tight chamber where the heating process is carried out ( The electrical wire connection from the electrical component to the control box and the heating coil at the outside of the oven was completed by the local electrician. baking chamber to make the oven food grade and to minimize heat loss as well. The baking chamber is equipped with two electric heaters of 1000 W power each, one at the top and another at bottom of the chamber. Two trays and temperature sensors are arranged in the middle of the baking chamber.

| Design of the control box
The control box contains the control panel instrument of the electric oven. The control box of the electric oven is made of mild steel sheet of 16-gauge thickness having the dimension of 30 × 20 × 24 cm (length × width × height). It contains 60 conductors, three magnetic circuit breakers, temperature meter, timer, and light indicator.
Temperature meter and light indicator were set outside the wall of the oven and other parts are placed inside the box.

| Design of the oven tray
The dimension of the tray was selected as 55 × 35 cm (length × width) to accommodate inside the baking chamber (Table 2). Two trays are provided in the oven cavity; both trays are made of stainless steel sheets of 1 mm thickness. The oven works by the convection process that enhances the movement of the hot air to the upper and lower tray of the oven eventually. The distance from upper tray to the lower tray was kept at 10 cm.

| Selection of the heating coil
The bimetallic thermometer ranging the temperature from 0 to 300°C was placed in the side wall of the control box. The thermometer sensor will be placed in the center portion of the baking chamber to ensure that the thermometer should detect the temperature of both the lower and the upper layer of the electric oven.

| Fabrication of the electric baking oven
The fabrication and assembly works of different parts of the electric oven were carried out using the data obtained from the above computations ( Figure 1). All the parts of the oven such as housing unit, baking chamber, perforated covers for heat distribution, heating coils, and temperature sensors were fabricated using locally Finally, the specific energy consumption was calculated as total energy/total product in a batch.

| Calculation of specific thermal energy required for baking of products
The specific thermal energy required for baking was calculated according to the equation.
where average baking (oven) temperature = T, average mass of a cake/ biscuit = m b , specific heat capacity of cake/biscuit = C b , ambient temperature = T 0 , and total baking time = t.

| Biscuit preparation process
Whole-grain wheat flour of the Pusti brand was collected from a local vendor, Dinajpur (Table 3). The moisture and protein content of Butter was cut into pieces and flour was added to it. After that, flour and butter were rubbed until the mixture is crumbling. Powder sugar and milk powder which contain 24% protein and 39% fat were added at a time and mixed properly to make smooth dough holding for 15-20 min for proper aeration. Dough was rolled in a wooden chapatti roller and wheat flour was dusted into the batter. Then, the dough was cut into desired round shape using biscuits mold. Finally, biscuits were placed on oiled tray and baked at 200-210°C for 20-25 min.
After baking, the tray was removed from the oven and cooled on a rack for 20-25 min.

| Cake preparation process
Whole-grain wheat flour along with all necessary ingredients was collected from a local market, Dinajpur, for making cakes (Table 4).
After that, about 88 g egg was taken into a bowl and mixed well with a mixer for 3 min. After mixing of egg, sugar, butter, and milk powder were added and mixed well. Therefore, flour of Pusti brand and baking powder were added to the batter and mixed properly. No water was added to the batter. Finally, the mixture was poured into a plain cake pan and baked at 170-180°C for about 25-30 min. The baked product was removed from the oven and cooled on a rack for 15-20 min at ambient temperature.

| Specific volume of cakes and biscuits
Volume of cakes and biscuits was determined with rapeseed replacement method and the specific volume of cakes and biscuits was calculated as the ratio of volume to weight (cm 3 /g) according to the method described in AACC (2002).

| Sensory attributes of baked product
Sensory analysis (color, flavor, taste, texture, and overall acceptability) of cakes and biscuits was evaluated by 30 semitrained panelists using a 9-point hedonic rating scale according to Lawless and Heymann (2010). Randomly coded samples were presented to 30 semitrained panelists and asked to rate the color, flavor, texture, and overall acceptability on a 1-9 point scale, where 1 = dislike extremely, 2 = dislike very much, 3 = dislike moderately, 4 = dislike slightly, 5 = neither like nor dislike, 6 = like slightly, 7 = like moderately, 8 = like very much, and 9 = like extremely.

| Statistical analysis
The obtained data from sensory attributes were expressed as mean ± standard deviation. Data were analyzed by SAS (Version 9.3) statistical software. One-way analysis of variance was done using ANOVA procedures. Significant differences among the means of response values were determined by Duncan's multiple-range test (DMRT) at the 95% confidence level.

| Design and fabrication success of the electric baking oven
An electric oven was successfully designed and fabricated as per

| Baking characteristics of the electric baking oven
The electric oven was found to bake food by heating elements placed in the oven after being heated to the desired temperature. Different types of products were baked in the electric oven. A total time 15-28 min was required for baking of cake and 18-35 min was required for baking of biscuits based on the shape and size of cakes and biscuit.
It took lesser time thus found to be less expensive than gas ovens.
It can bake food evenly and quite easily. It is equipped with buttons that need to be pressed to achieve the desired set temperature. It is also easy to clean and maintain. Loaf volume of each cake (with TA B L E 3 Ingredients for making biscuits.

| Performance analysis of electric baking oven
The performance of the electric oven was analyzed according to different parameters such as obtained desired level of temperature, time to raise baking temperature, and consumption of energy during baking which has been in the following section.

| Evaluation of temperature in the oven during baking
The electric baking oven was tested in order to determine the maximum temperature generated in the oven and for the calibration of the thermostat. After assembling the oven, the first experiment was done with it using a thermometer and a timer to discover the effective heating of the oven. A certain temperature is fixed such as 180°C and temperature was recorded in 5 min intervals, and a graph was plotted with time and temperature, where the X axis represents time and the Y axis represents temperature (Figure 4). The graph showed the fluctuation of temperature to be about ±5°C and higher temperature was recorded at 185°C and lower temperature was at 176°C, which indicated better performance than other electric ovens as reported by Olugbade and Ojo (2018) and Ologunye et al. (2020).

| Temperature raises experiment in the oven
The oven was heated with electric energy and temperature was recorded at every 1 min interval. The recorded value was plotted into a graph where the X axis represents time and the Y axis represents temperature. From Figure 5, it has been shown that the oven heating coil reached its maximum heating temperature in 18 min which is 250°C.

| Measurement of time required to cool the oven
The oven was heated with electric energy until its temperature stabilized. Then, electric energy was disconnected and the fall in F I G U R E 2 Front view of the electric baking oven.

Control box Indicator
Temperature meter F I G U R E 3 Rear view of the electric baking oven.

Heater
Temperature sensor temperature of the electric oven was recorded. The results of fall in temperature are shown in Figure 6. It has been seen that the temperature fall evolution of the oven with time.

| Electric energy consumption of the oven
Current and voltage were recorded when the oven was running and a graph was plotted which showed the relationship between current and voltage at different times as shown in Figure 7; we found maximum current as 9.63 A and voltage of 240 V.

| Specific electric energy consumption of the oven
During the period of baking, electric energy was converted to heat and used to remove moisture from baked products. For calculation of unit cost of baking, it is important to determine the energy consumption of the oven (Table 5) Besides, temperature controller was used to control temperature inside the oven at a certain range. Therefore, temperature was set at 180°C for baking cakes; it turns OFF the heater when temperature reached the desired level. After a certain period, temperature varies at 180-185°C and then gradually starts to decrease.
When the temperature reached 178°C, again heater was turned ON and produced heat until it reached 180°C. For calculation of energy consumption, time was recorded during it turned OFF and ON because in turned OFF time, no energy was used by the oven.
During calculation of unit cost per hour in the oven, it is important to know how much time the heater of the oven was running. Table 5 shows the recorded data for calculation of unit cost per hour. From Table 5, it has been seen that total running time of the oven in 1 h was 15.5 min. So, using Equation 2, we calculate the specific electric energy consumed in 15.5 min, when the oven running at 1 h was 0.59 KWh.

| Baking performance of electric baking oven
3.9.1 | Baking time for different products Different types of products were baked in the electric oven such as cakes and biscuits. The time required to bake cakes and biscuits depended on size and shape of the products. Generally, larger-size cakes required much more time than smaller ones. The time required to bake different sizes of plain cakes and round biscuits is shown in Table 6. Color, flavor, and texture of biscuits were also acceptable. Brunet  This may be due to mixing ingredients difference during making batter (Figoni, 2011).

| CON CLUS IONS
An electric baking oven was designed and fabricated with locally available materials from a local workshop by local technicians. Mild steel sheet and stainless steel sheet were used for the construction of the outside and inside of the body, respectively, of the oven. Glass wool which has thermal conductivity of 0.04 (w/m K) was used as the insulating material. A temperature control device was also used to ensure that the oven temperature can be regulated properly. The oven was constructed for home use and small entrepreneur because of its small size. The simplicity of the oven makes it unique with various advantages such as easy to fabricate, easy to clean, easy to disassemble and assemble, low cost for a family of average income, portable, allowing fast baking time, and making the cooking of conventional foods efficient. There was no significant difference between sensory attributes of commercial cakes and improved baking oven cakes. On contrary, significant difference was observed in biscuits. Therefore, the proposed oven can be one of the most suitable electric baking ovens for baking cakes and biscuits. However, this research has an opportunity for further modification, development, and fabrication of electric baking ovens for small household units and at a scale for the production of quality baked product.

ACK N OWLED G M ENTS
The authors acknowledge the Institute of Research and Training

CO N FLI C T O F I NTE R E S T S TATE M E NT
The authors declare no conflict of interest.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data supporting the findings of this research will be available on request.

E TH I C A L A PPROVA L
Ethics approval was not required for this study because this is not a medical study nor any nutritional trial was conducted on humans.