Evaluating the Efficiency of Areke Distillation Process Using the Traditional Method of Distillation and Double Pipe Distillation: A Traditional Ethiopian Beverage

2.1 The study area

The study was conducted at the Debre Markos microbiology laboratory of the Department of Biology and Mechanical Engineering Department Workshop, Debre Markos University, Ethiopia. The location of the university in the town of Debre Markos, which is situated at latitude and longitude 10020′N 37043′E/10.3300N 37.7170E and 2,446 meters above sea level. Debre Markos is found 265 kilometers from Bahir Dar and 300 kilometers from Addis Ababa, the capital of Ethiopia. In Debre Markos, 107,684 residents comprise 49,893 men and 57,791 women.²⁰ The lowest and highest temperatures are 15°C and 22°C, respectively, while the average annual rainfall is 380 mm.

2.2 Areke distillation equipment

Developing a prototype of the areke distiller equipment and gathering various engineering materials were the initial steps in improving the efficiency of traditional areke fermentation distillation. The required equipment for developing a prototype of the areke distiller were a heat exchanger, condenser, energy saving stoves, fermentation equipment, storage tanks, and local areke extraction apparatus. The areke distiller equipments were purchased and manufactured the prototype of the areke distiller apparatus by technicians (welders).

2.3 Manufacturing double pipe heat exchanger

A double-pipe heat exchanger (surface condenser) was used to condense ethanol vapor. The outer pipe was constructed by using polyvinyl chloride with a length of 120 cm and a diameter of 3.81cm (Figure 1 S⁴¹). A large volume of cold water was transported effectively to the outside pipe because the substance is inert and cannot react with other materials to cool. The internal pipe was made from copper pipe and stainless steel pipe with a length of 140 cm and a diameter of 1.27 cm. The outer pipe and the holes between the outer pipe and internal pipe were sealed using sealing material.

2.4 Stove Construction for areke production

A modified Areke stove and a traditional stove were the two biomass stoves used in the study experiment. Energy-efficient modified areke stoves were constructed and evaluated at the areke vendor houses for alternative stove types with six stoves in a row, four stoves in a row, two stoves in a row, and one stove. The traditional areke stove was constructed out of mud and then painted with wet manure. A modified fire stove (midija) was made from bricks and mud. Smaller granules of crushed clay were sieved through the 4 mm sieve to obtain fine granules. The sifted sawdust and clay in a ratio of 1:1 were mixed by adding water to make it moldable. A closed fire stove (midija) was used to save heat from going out. The bowl-shaped cover was made up of clay to fit well with the clay pot and double pipe.

2.5 Substrates used in local areke production

Five different kinds of cereal crops were utilized to produce local areke such as millet (Pennisetum glaucum L.), wheat (Triticum aestivum L.), lupine (white lupine L.), barley (Hordeum vulgare L.), and maize (Zea mayz L.). Areke was made through distillation from various ratios of water, ground gesho (Rhamnus Prinoides L.), and cereals.^4,11,21 A variety of grains (maize, barley, lupine, wheat, and millet) were purchased at the neighborhood market.

2.6 Traditional areke fermentation process

Yereke-tensis , medifedef, and areke are the three basic processes in the areke production process (Figure 3 S).^4,7,21,22,41 The traditional areke fermentation process was prepared by an experienced woman brewer using a mixture of ingredients with appropriate steps and procedures in Debre Markos City at Bole kebele, which is held by a private areke producer with paid in cash.

2.7 Components of double pipe areke distillation

Big pots (metensesha) from the local alcohol distiller were used as fermenters. A small clay pot (Madiga) was used to boil the fermented mash to release vapor. The cloth was used to seal the madiga to prevent vapor losses. Hollow tubes of copper and stainless steel were used as a pipe to transport the vapor of areke that comes from the clay pot (boiler) to the collector. Koda was used as a collector. The tubes were made of metal or aluminum to collect the vapor that passed through them. Tofaa made of clay was used to contain cooling water in which koda vapor changed into a liquid. A traditional distillation apparatus of the bamboo tube (a pipe to transport vapor that comes from the boiler to the collector) made from hollow plant steam (Bambusa vulgaris L.) was used as a control according to the method of distillation described.^3,14

2.8 Evaluation of stove and double pipe efficiency

This study was conducted to evaluate the efficacy of a traditional stove, a modified stove, and a combination of a modified stove and double pipe in terms of firewood consumed, time of operation reduced, and productivity of alcohol (Figure 2; Figure 4 S⁴¹). The quantity of fuelwood used at a household level was estimated by measuring fuelwood in kilograms (kg) using a spring balance. The calculation of efficiency firewood, time of operation is reduced, and productivity of ethanol amount were calculated according to the Refs. 23, 24 and 25 equation, respectively.

2.9 Determination of ethanol level

The specific gravity and refractive index were measured to estimate the ethanol level using the technique of.²⁶ The samples’ specific gravity and refractive index were determined at 20°C. Samples of ethanol concentration was determined using a hydrometer (to measure specific gravity) and a refractometer (to record sugar content). A refractometer (Model, 2WA) was used to measure the refractive index of the areke samples. A single drop of ethylic alcohol was used for calibration after the prism had been cleaned with ethylic alcohol. The apparatus was set up so that half of the field was illuminated and the other half was left in the dark. The refractive index was then determined by placing a drop of areke on the sample holder. The ethanol content (%) was calculated according to the equation below: Ethanol content = R − [(S.G.−l) × 1000] where R = refractometer reading, SG = SG = specific gravity.

2.10 Sensory evaluation of areke

Sensory evaluation of areke samples was estimated by ten consumer sensory panelists. The average age of the panelists was between 25 and 50 years old. Ten judges who had previously consumed alcohol were chosen from the community based on interest and availability. Sensory parameters such as flavor, color, alcoholic strength, and overall acceptance of areke were evaluated using a hedonic scale of 1 to 5, where excellent = 5, very good = 4, good = 3, Fair = 2, and poor = 1. Sensory attributes (color, taste, alcoholic strength, and overall acceptability) were assessed utilizing the technique of.^27–29

2.11 Data analysis

The SPSS version 23.0 IBM SPSSInc., Chicago, IL, SPSS (RRID: SCR_002865) (https://www.ibm.com/support/pages/downloading-ibm-spss-statistics-23) was used to evaluate the data. The averages and standard deviations of the triplicates analysis were determined using analysis of variance (ANOVA). Tukey’s multiple range testing was defined as the statistical significance (p < 0.05).

2.12 Ethical consideration

The present study was approved by Debre Markos University, Natural and Computational Science College of Ethical Review Committee approval number (Ref No. DU/NCS/12/2024) on the date of approval, 10^th December 2024. The study adhered to the ethical principles outlined in the Declaration of Helsinki. Participants verbally consented to promote a more conversational dialogue than a written form. Participants verbally consent were approved by the ethical committee. The participant consent was waived by ethical approval committee because the study involved minimal risk to participants, did not adversely affect their rights of participants. and their potential benefits to society. Participants verbally consented on 7^th May 2024 for their data to be used. All data were deidentified using the Safe Harbour method to ensure the protection of personal and sensitive information.

3.1 Physicochemical properties of areke

The physicochemical properties of areke from traditional distillation (C) and double pipe distillation (E) are shown in ( Table 1). There was no statistically significant (p ≥ 0.05) difference between barley E (gebis E) and wheat E (sinda E) in ethanol content of areke samples. The study indicated that the double pipe distillation (E) produced a higher ethanol concentration than the traditional distillation (C). The highest concentration of ethanol of the areke was achieved through double pipe distillation (E) from millet E (dagusa E) 53.75 ± 0.01 (% v/v). The minimum ethanol concentration of the areke was achieved through traditional distillation (C) from lupine C ( gibeto C) 24.19 ± 0.05 (% v/v). Medium levels of ethanol were found in five of the areke samples of millet E (dagusa C), maize E (bekolo E), barley C ( gebis C), and lupine C ( gibeto C). The double pipe and traditional distillers areke ethanol contents are consistent with those reported in other studies,^7,12,30 which implies that areke ethanol content can vary greatly. The differences in ethanol contents of areke may be because of variations in cereals crops, methods of preparation, fermentation, and modified distillers.^31–34

The average specific gravity of traditional distillation areke ranged from 0.99 ± 0.00 to 0.92 ± 0.01 ( Table 1). Barley C ( gebis C) and lupine C ( gibeto C) exhibited higher specific gravity than the other areke samples. The double pipe distillation areke had a mean specific gravity that varied between 0.96 ± 0.02 and 0.92 ± 0.01. The average areke samples of refractive indices varied between 1.42 ± 0.01 and 1.33 ± 0.00. A higher refractive index was obtained from barley C ( gebis C) than other areke samples. The finding of mean specific gravity and refractive index in this study was consistent with the work of other researchers.^25,35–37 This is due to differences in the levels of fermentation and distillation efficiency. These are due to variations in fermentation and distillation efficiency levels.

3.2 Sensory evaluation of areke

The sensory test (taste, color, alcoholic strength, and general acceptance) of areke was conducted by a panel of ten people, and the average results are shown in Table 2. Lupine C ( gibeto C) had the lowest score (2.2 ± 0.01) among the measures for overall acceptance compared to the other parameters. The highest score attributed was obtained from maize E (bekolo E) (4.5 ± 0.01) parameters of overall acceptance than other areke sensory parameters. The alcoholic strength of lupine E ( gibeto E) was scored excellent (5.0 ± 0.01) to other areke sensory parameters. The taste of maize E (bekolo E) (5.0 ± 0.01), and wheat E (sinda E) (5.0 ± 0.02) areke were scored excellent based on the sensory assessment. There was a statistically significant (p < 0.05) difference between lupine E ( gibeto E), lupine C ( gibeto C), and maize E (bekolo E) in the overall acceptance of areke samples. The overall acceptance of double pipe distillation of areke samples was higher than the traditional distillation of areke samples. All judges agreed that the tradition and double pipe areke consumption was acceptable based on their sensory evaluations. Sensory evaluation of areke is strongly affected by the method of preparation and usage of gesho in the preparation, which in turn plays an important role in the perception of the people.^2,12,38,39 The heat provided during the boiling stage has a significant impact on the final distilled areke flavor, aroma, color, and alcoholic strength.²⁵

3.3 Evaluation of stove and double pipe efficiency

The average amount of firewood used was reduced by 50% ± 0.15 when double pipe distillation combination with a modified stove ( Table 3; Figure 4 S⁴¹). The percentage of areke (v/v) increased by 68.5% ± 0.01 when the combination of a modified stove and double pipe distillation was used. The amount of areke produced from traditional distillation was 1013 ml ± 1.00, and the temperature of the areke was lowered to 61°C ± 1.00 as soon as the distillation stopped ( Table 3; Figure 2⁴¹). The amount of areke in the modified stove distillation was increased by 1014 ml ± 0.57, and the temperature of the areke was lowered to 60°C ± 0.57 as soon as the distillation stopped. The amount of areke in double pipe distillation was increased by 1141ml ± 1.00, and the temperature of areke was reduced by 35°C ± 1.15 as soon as distillation stopped. The amount of areke in a modified stove and double pipe distillation increased by 1253 ml ± 0.92, and the temperature of the areke dropped by 35°C ± 0.58 as soon as the distillation stopped. Firewood consumption was higher in the traditional open fire stove (5.1 kg ± 0.1) than in the modified stove (3.5 kg ± 0.01). A total of 2.5 kg ± 0.01 of firewood was needed to distill using a combination of a modified stove and double pipe distillation ( Table 3; Figure 4 S). Traditional distillation and modified stove distillation were not statistically significant (p > 0.05) in terms of areke productivity, the temperature at the end of distillation, or the volume of areke produced. According to Temesgen and Kamil,¹⁵ the time used by the modified (mirt) areke stove was reduced by over 50% by the stove with three stones (52%; 1:04 h: min). The time of modified areke stove reduces brewing time by 22% than the traditional areke stove.¹⁴ The modified areke stove emits less smoke and uses less firewood to distill areke than a traditional stove.^15–17,40