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A comprehensive physical and cup quality assessment of coffee (Coffea arabica L.) has not yet been conducted on Kafa Biosphere Reserve coffees. Hence, the influence of location, production systems, and processing methods on coffee bean physical and sensorial qualities were studied to identify the inherent qualities and suitable preparation methods for the improvement of bean physical and organoleptic qualities. In a three-stage nested design, factors such as location (Gimbo, Gawata, and Decha districts), coffee production system (forest, semiforest, and garden), and processing method (wet, semiwet, and dry) were considered. Preliminary coffee quality assessment data were gathered from bean physical and cup quality analyses of coffee obtained from the combination of the three factors. An ANOVA was conducted on preliminary coffee quality data. The result of the ANOVA showed that location and production system effects were significant only on bean moisture content (P < .01) and acidity (P < .05), respectively. The processing effect had a significant effect on bean moisture (P < .01), odor (P < .001), raw (P < .01), and preliminary grade (P < .05). Better coffee quality was maintained in the dry coffee processing method within the recommended moisture content. Forest and semiforest coffees respond poorly in odor and overall raw coffee quality when treated with wet and semiwet processing methods. Hence, to attain a better quality of coffee, rather than proper harvesting procedures, more emphasis should be given to choosing proper processing methods. Further investigation that includes the effects of elevation gradient is recommended.
Coffee is a commercially valuable commodity and is the most popular beverage globally. For many producing countries, it is a major foreign currency source and contributes a lot to tax income and gross domestic product (ITC, 2011). For coffee-producing countries, the production and supply of coffee for the international market is a challenging process since its value is governed by bean quality (W. T. Gole et al., 2015; Stanculescu et al., 2011). In 2020, Arabica coffee (Coffea arabica L.) accounted for 59.27% of the world's coffee production (ICO, 2021a). In Ethiopia, coffee is grown on 0.76 million ha of land, and more than 529,000 tons of coffee beans were estimated to be produced in the 2019–2020 cropping season (CSA, 2020). This makes Ethiopia Africa's leading coffee-producing country; it produces and exports 7.35 and 3.98 million 60-kg bags of coffee beans, respectively (ICO, 2021b). In the 2017–2018 production year, 34% of Ethiopia's exports were covered by coffee (GAIN, 2019).
Arabica coffee is an integral part of the southwestern Ethiopian tropical forest agroecology (T. W. Gole & Senbeta, 2008). A large portion of the forest ecosystems are undergoing various changes. Deforestation and the expansion of agricultural lands have modified the coffee-growing regions for habitat destruction and are putting the coffee genetic resources in danger. The forest ecosystems create not only conducive conditions for producing distinctive quality coffee, but also a source of income for the livelihoods of coffee-producing communities that rely on the systems to produce honey and nontimber forest products (NABU, 2021). Hence, to preserve and sustainably utilize Arabica coffee genetic resources, the Kafa Biosphere Reserve was established in 2010 as a UNESCO (United Nations Educational, Scientific, and Cultural Organization) registered area (W. T. Gole et al., 2015; UNESCO, 2021). In this specific agroecology, it is possible to get exemplary coffee quality. However, for producers, it is hard to get proper market value and maintain it for longer (Samuel & Ludi, 2008).
Coffee production and processing systems are the primary factors that determine the overall quality of coffee produced in a specific environment (ITC, 2011). Changes in altitude, rainfall pattern (Cheserek & Gichimu, 2012; Leonel & Philipe, 2007), temperature, relative humidity, light, moisture, and soil nutrients (Bedimo et al., 2007; DaMatta, 2004; Steiman, 2013) all have a significant impact on the growth and development of the coffee plant, and thus the final beverage quality of coffee beans (Barbosa et al., 2012; ITC, 2011). The change in the final liquor quality of coffee results from important biochemicals that are influenced by the abovementioned environmental conditions (Sridevi & Giridhar, 2013).
Management practices applied during the production and the varieties used to produce coffee define the four coffee production systems practiced. Accordingly, forest, semiforest, garden, and plantation systems describe Kaffa coffee production systems. Forest, semiforest, and garden systems are categorized as traditional production systems, which are managed mostly by small-scale farmers, whereas a commercial/plantation system is a modern one and uses improved technologies (KFCCU, personal communication, 2016; Regassa et al., 2013).
Forest coffees grow naturally under dense canopy layers, and no management activity is applied, but with slight weed clearance to allow movement during harvesting (T. W. Gole et al., 2001). The coffee plants are grown at high plant density, and the beans are harvested at their early development stage. Semiforest production system coffees are wild coffees grown under natural conditions (Degnet, 2005). Due to the removal of understory shrubs and weeds, more coffee seedlings are allowed to grow and increase the diversity of the coffees unless tree density management is applied (Regassa et al., 2013). Generally, weed control is conducted twice a year, before harvesting and at the onset of the rainy season. It has a reduced canopy layer (large trees), but legume tree species grow preferably with highly disturbed lower strata. Garden coffees are homestead coffees grown with intensive management. Weeding is applied two to three times per year, fertilized with farmyard manure and crop residues, mostly by hoeing and intercropping with other crops (T. W. Gole et al., 2001). The system has significantly reduced shade levels. Since coffee plants are allowed to grow after being selected and raised with intensive human care, the diversity of the coffee plants is reduced as compared with the previous systems (Regassa et al., 2013).
- Coffee production location differences have a significant effect on bean moisture content.
- Coffee production system effects can significantly affect the acidity of coffee cup quality.
- Coffee processing had a significant effect on bean moisture, odor, raw, and grade.
- The dry coffee processing method maintained cup quality of coffee better than wet methods.
Lack of proper harvesting and processing methods is thought to be a contributing factor to the poor quality of coffee (ITC, 2011). Globally, wet, and dry coffee processing methods are commonly practiced in coffee-producing countries. Coffee varieties treated with these methods have exhibited significant quality variations (Sualeh et al., 2014). On the other hand, a semi-wet method, which is relative to the wet method, is cost-effective and easily practiced by processors in areas where water shortages exist (Ethiopian Coffee and Tea Development and Trade Authority, unpublished data, 2016). In Ethiopian conditions, it has resulted in a comparable quality grade when applied with a mucilage removal procedure (Tolessa et al., 2016).
Kaffa Biosphere Reserve is not only an in situ arabica coffee conservation area; farmers continue to harvest coffee in buffer and transition zones with minimal management activities (Dresen, 2011; T. W. Gole et al., 2002). In the area and generally as a country, the applied production systems and related factors make the coffee traded as conventional or specialty in the world market. In the Kaffa zone, specifically in the Kafa Biosphere Reserve, although coffee production is mostly forest-based, the shade type and intensity, the genetic makeup and age of the coffee, and the management practices applied are so variable (W. T. Gole et al., 2015; NABU, 2016). Hence, these factors could affect plant growth, development, and the overall quality of the coffee. However, there is no detailed assessment of the quality of coffees produced in different production systems and best-suited, cost-effective processing methods for resource-deficit farmers. Furthermore, as part of an ongoing effort to conserve the biosphere for sustainable use of coffee resources and improve the livelihoods of coffee producers in the area. Thus, we hypothesized that the effects of variations in location, coffee production systems within locations, and processing methods within production systems and locations could significantly affect the quality of coffee. As a result, we were able to identify an important factor and point out an alternative means for quality coffee production considering the existing environmental variations. Therefore, we have executed the current study to find out the effect of location, coffee production systems, and processing methods on the quality of Kafa Biosphere Reserve coffees to better understand their inherent qualities and identify suitable processing methods for the improvement of bean physical and organoleptic qualities.
2 MATERIALS AND METHODS
2.1 Description of the study areas
The study was conducted in three districts (Woredas) within the Kafa Biosphere Reserve in 2018. The biosphere is situated in the Kaffa Zone, in the southwestern part of Ethiopia. The Kaffa zone covers 10,602.7 km2 and is found within altitudinal ranges extending from 500 to 3,500 m asl. It has highland, midland, and lowland agroecologies with a share of 11.64, 59.45, and 28.91%, respectively. It has an annual rainfall of 1,000–2,200 mm and an average minimum and maximum air temperature of 10.1 and 27.5°C, respectively (SNNPRG-IEMP, 2016). According to agroecological classification, the area is categorized under humid agroecology (NABU, 2016), and topographically, it is uneven and undulated due to subsequent geological changes (Chernet, 2008). Regosols (dystric) soils are dominant soil types up to 50 cm in depth (Schmitt, 2006). The representation of each district in the biosphere reserve sampling sites’ average elevation point and their 10-yr average weather conditions are depicted in Table 1.
|Districts||Representation in the biosphere||Avg. elevation||Rainfall||Min.||Max.||Relative humidity|
- Note. Source: Nature and Biodiversity Conservation Union (2016); National Meteorological Agency (unpublished data, 2020).
According to the zonal Office of Agriculture report (2019, not published), more than 281,000 ha of land were covered by coffee. Out of the total area, 57.6% was covered with garden coffee, 19.3% with forest, 18.3% with semiforest, and the rest (4.8%) was plantation coffees.
Proper coffee sample collection sites were selected inside Boginda and Bonga forests based on their elevation gradients (1,600–1,900 m asl), and the points were georeferenced (GPS Garmin Etrex 30) by recording latitude and longitude. In the forests, buffer zones in which farmers can manipulate and harvest coffee (T. W. Gole et al., 2002) were considered to select forest and semiforest coffees for sampling. In addition, garden coffee production system coffees were collected from representative farms. A three-stage balanced nested design that can effectively accomplish random effects ANOVA of balanced nested design data through estimating components of variance and testing their significance (SAS Institute, 2008) was used for site selection in the study.
2.2 Sampling techniques and sampling procedures
The study comprises coffee cherry sampling from three (Gimbo, Gawata, and Decha) districts (Figure 1) and three coffee production systems (forest, semiforest, and garden); three processing methods (wet, semiwet, and dry) were applied to collected cherries. Thus, there is no specific variety that is considered in this specific study. However, in the forest and semiforest production systems, coffee production mostly depends on the wild Coffea arabica landrace (NABU, 2016). In particular, forest coffee production is conducted without the addition of inorganic fertilizer, and this is because the presence of shade and related mineralization of litter affects the overall requirement of nutrients for the coffee crop (Anteneh, 2015). In the garden coffee production system, although traditional landrace cultivars and generally different types of coffee are used, improved cultivars are introduced into the system. There is intensive crop management, such as frequent weeding, fertilization with farmyard manure and crop residues, and intercropping with other crops (T. W. Gole et al., 2001).
Fully ripe red coffee berries (15–18 kg) were collected by hand picking at the time of maturity from October to December 2017. Cherries were collected from randomly assigned 20–30 trees to get 3 kg of green coffee beans based on the conversion ratio (Sualeh & Dawid, 2014). In the study, 36 independent coffee samples were collected from all districts (12 samples from each), and four replicated samples were collected to represent three production systems. Each sample was divided into three equal amounts to apply the three processing methods, and this made a total of 108 samples from all three districts for final quality analysis.
2.3 Coffee samples processing methods
Coffee cherry processing was conducted based on Ethiopian recommendations at Bonga Agricultural Research Center. The center is situated in the Gimbo district at an elevation point of 1,740 m asl. The district receives 1,735–2,545 mm of rainfall per year, with minimum and maximum temperatures ranging from 11.70 to 28.40°C and an average relative humidity of 73.39% (National Meteorological Agency, unpublished data, 2020). Before the application of the processing methods, the harvested cherries were cleaned of immature berries and foreign materials. For wet processing procedures, harvested cherries were pulped using a manual pulping machine (Mckinnon India). The parchment coffees were fermented for 48 h, washed, and a final soaking was conducted for 16 h to loosen the remaining mucilage. Then, at the end (at 64 h), the coffees were washed and sundried on a raised wire mesh panel. For semiwet processing, cherries were pulped, washed, and sun-dried (Ethiopian Coffee and Tea Development and Trade Authority, unpublished data, 2016). For dry processing methods, the collected cherries were sun-dried. All samples were sun-dried until the required moisture content (11.5–12%) was attained (determined using a Mckinnon digital moisture meter) (ECX, 2015). Before quality analysis, the coffees were hulled manually, cleaned, and packed (0.6 kg) in a clean plastic bag and stored at room temperature (Farah, 2012).
Coffee bean physical and liquor tests were conducted at the Ethiopian Commodity Exchange (ECX) Bonga Branch with Q-grade cuppers who were able to cup consistently with the Coffee Quality Institute (CQI) protocols and procedures and demonstrate a working understanding of the cupping form (CQI, 2021). Screen 14 and moisture content tests were conducted. For raw analysis, defective beans and foreign materials were sorted out to calculate primary and secondary defects. For unwashed or dry-processed coffees, the raw value was assessed with a 30% defect (15% for primary and secondary defects each) and an odor of 10%. Apart from this, the raw value of wet/semiwet processed beans was measured by 20% defects (10% for primary and secondary defects each), shape and make (5%), color (5%), and odor (10%). For cup quality taste, 100 g of beans were roasted for 8–12 min, cooled, ground, and put into 250-ml cups. Finally, the brew was ready for three cuppers for respective tasting procedures that included cup cleanness (15%), acidity (15%), body (15%), and flavor (15%) for wet, semiwet, and dry-processed commercial coffees. Finally, the summation of both raw (40%) and liquor (60%) values was used to categorize coffee samples based on preliminary assessment grades (ECX, 2015).
2.4 Data analysis and presentation
An ANOVA on the collected data was performed using SAS version 9.3 (SAS Institute, 2012). Significant differences were declared when the obtained P values of the factors were less than .05. Differences between least-square means among factor levels and combinations were determined by using the Tukey's test (honestly significant difference) at 0.05, 0.01, and 0.001 probability levels.
The results revealed that the green bean moisture content of Kafa Biosphere Reserve coffees was significantly (P < .01) affected by the location effect. Whereas above-14 screen retention was not significantly affected (P > .05) due to the location difference. Significant location effects were not detected (P > .05) on raw quality (odor and raw total), cup quality (acidity, body, flavor, cup value), total value, and grade. The effect of production systems was not significant (P > .05) on moisture content and above-14 screen retention. Except for acidity (P < .05), the effect of the production system was not significant (P > .05) on the all-preliminary coffee quality variables. The processing method effect was significant (P < .01) on bean moisture content, but not on above-14 screen retention. Furthermore, it was significant for raw quality variables (odor [P < .001] and raw value [P < .01]). Except for preliminary grade (P < .05), cup quality variables and total value were not significantly affected by processing methods (Table 2).
|Source of variation|
|Dependent variables||Districts||Production systems||Processing methods||Grand mean||CV||R2|
|Screen 14 retention||6.694ns||1.407ns||1.213ns||98.22||0.88||.42|
|Odor||1.231 ns||0.546 ns||0.787***||9.82||4.77||.53|
|Raw value||18.120 ns||28.102 ns||17.120**||35.70||7.16||.49|
- Note. CV, coefficient of variation; ns, nonsignificant.
- * Significant at the .05 probability level.
- ** Significant at the .01 probability level.
- *** Significant at the .001 probability level.
The least-square mean variations were observed between the green bean coffees of the Kafa Biosphere Reserve. As a result, Gimbo and Decha district coffees had higher bean moisture content (>11%) than Gawata district coffees (11%) (Table 3).
|Districts||Moisture content (%)||Screen 14 (%)||Odor (10%)||Raw value (40%)||Acidity (15%)||Body (15%)||Flavor (15%)||Cup value (60%)||Total (100%)|
- Note. The least square means with the same letter in a column are not significantly different.
Most of the coffees that come from each district are better in acidity (12.00–12.25). Though it was not significantly different from the remaining better acidity scores, Gawata forest coffees exhibited poor acidity (11.75) scores, whereas significantly poor acidity (10.75) was observed on garden coffees of the same district (Table 4).
|Districts||Production system||Screen 14 (%)||Moisture content (%)||Odor (10%)||Raw (40%)||Acidity (15%)||Body (15%)||Flavor (15%)||Cup (60%)||Total (100%)|
- Note. The least square means with the same letter in a column are not significantly different.
Except for forest coffees of the Decha district, dry processing has exhibited consistent moisture content across locations. A relatively higher (12.08) moisture content was recorded on wet-processed garden coffees of the Gimbo district. On the other hand, significantly reduced moisture content was recorded on wet and semiwet processed Gawata district forest and semiforest coffees (Table 5).
|Dependent variable||Processing method||Forest||Semiforest||Garden||Forest||Semiforest||Garden||Forest||Semiforest||Garden|
|Bean moisture (%)||Wet||11.58a–f||11.93ab||12.08a||10.65efg||10.30g||10.83b–g||11.68a–f||11.73a–e||11.60a–f|
|Screen 14 (%)||Wet||97.75||98.50||97.25||99.00||99.00||98.50||98.75||97.50||98.25|
- Note. The least square means with the same letter under each variable are not significantly different.
The coffee odor was significantly better (9–10) across all processing methods except wet-processed Gawata forest coffee (8). A better raw score was observed on all the dry-processed coffees of each district production system. However, most of them were not significantly different from the rest. The top (39.25) raw score was recorded from Decha district dry-processed garden coffees; on the other hand, the two lowest (32.25) scores were from wet and semiwet processed Decha district forest and semiforest coffees, respectively. Significant preliminary coffee quality grade variations were observed across processing methods within each production system. Although similar least-square means were recorded in most of the processing method and production system combinations, better preliminary coffee quality grades were recorded primarily from dry and secondly from wet-processed coffees of the districts (Table 5).
Concerning the studied factors, the processing method effect was relatively more responsive than location and production system effects on physical, raw, and cup coffee quality variables. The moisture content of green coffee beans should be within the proper range to reduce material loss, physical and sensory defects when it is high (>12%), and flavor loss when it is too low (<8 or 9%) (Gautz et al., 2008; Leroy et al., 2006). Although there is no single sample that is out of range, Gawata district forest-based coffees generally have a reduced amount of bean moisture, which coincides with poor flavor and cup scores. All Gimbo and Decha garden coffees with higher bean moisture content had better flavor and cup tests, which could be attributed to the genetic entity that garden coffees were intended to have through the inclusion of landrace and improved cultivars in the production system (T. W. Gole et al., 2001; Regassa et al., 2013). In contrast with the current finding, Sualeh et al. (2021) reported that the district and locations within the district did not show significant variations in the bean moisture content of southwestern Ethiopian green coffee beans. However, Morales-Ramos et al. (2020) reported a significant effect of green bean moisture content on the overall sensory attributes of southern Mexico's coffee.
The effect of the production system was significantly pronounced only in the acidity of coffee. Better coffee acidity was observed in most coffee production systems in the districts; however, a reduction in the score of acidity was exhibited on Gawata forest and garden coffees. According to ITC (2011), overdried beans (8%) are roasted faster than properly dried beans, so the acidity of coffee after roasting is reduced. In the current study, the moisture content of the beans is within the proper range (10.68–11.92%). However, Gawata district coffees had significantly reduced moisture content (10.68–11.01%), and this could be the reason behind the reduction of coffee acidity in this specific district coffee production system. On the other hand, the relatively poor acidity score of these production systems in the district could be related to soil chemical quality and related factors. A similar result was reported by Sualeh et al. (2021), in which acidity was affected significantly by the differences in district and locations within districts, though the production systems of the coffees were not stated clearly.
Contrary to our findings, a study conducted in Ethiopia across locations found that wet-processed coffees show a significant difference in raw quality scores but not in odor scores due to the difference in districts and locations within districts (Sualeh et al., 2021). In our study, the effect of coffee processing methods is more responsive to raw (odor and overall raw) quality and grade scores of coffees than district and production systems within districts. In this regard, the dry processing method topped the water-based processing method in scores of Kafa Biosphere coffees. Garden coffees respond well to all processing methods. Compared with dry methods, odor and overall raw quality scores become lower when forest and semiforest coffees are processed with wet and semiwet methods. This could be related to the genetic entity that the coffees in the production systems are from wild and semiwild populations (Geletu, 2006), and having relatively genetically diverse populations (Aga, 2005), they tend to respond poorly to wet-based processing methods. Since garden coffees are traditionally cultivated landraces, come from intensive selection (Labouisee et al., 2008; Nure et al., 2007), and are produced with intensive management and care (W. T. Gole et al., 2015), they could respond well to recommended coffee processing methods (Ameyu et al., 2017; Salla, 2009) as observed in the current study.
Coffee preliminary grade scores improved in the dry processing method regardless of location or production method. In Ethiopia, dry-processed Arabica coffee cultivars (Sualeh et al., 2015) and forest coffees (Yadessa et al., 2008) have been given better quality scores. The presence of pulp and mucilage (Worku et al., 2018) plays an important role in proper natural decomposition and protection of beans from undesirable environmental factors and enhances the characteristic fruity and cherry flavors in the final beverage quality (Poltronieri & Rossi, 2016). Furthermore, the absence of fermentation that lets the sugary mucilage and the silver skin polysaccharides remain adhered to the bean throughout the drying period (Farah, 2012; Knopp et al., 2006; Marraccini et al., 2007) could positively influence the final grade scores.
The result of the current study shows that the alternative hypothesis that is supposed to cause a variation in the physical and organoleptic qualities of the coffees because of district and production systems within districts was accepted, since their effect was significant on the bean moisture content and acidity of coffees. However, the alternative hypothesis that tests the effect of processing systems within the district and production system was accepted, since considerable variations in the scores of physical, raw, and overall quality of Kafa Biosphere coffees were significant. A tendency for a close relationship was observed between coffee acidity and bean moisture content. This was observed in Gawata district coffees, where reduced moisture content of beans was related to reduced coffee acidity. Hence, we need to keep bean moisture content high within the recommended range to get better cup quality, specifically coffee acidity. The study confirms that, in addition to the selective hand-picking of red-ripe berries, better quality coffees can be obtained by using the dry processing method within the recommended range of green bean moisture content. Compared with garden coffees, forest and semiforest coffees respond poorly in odor and overall raw quality when they are treated with wet and semiwet processing methods. The study identified the inherent qualities of the Kafa Biosphere Reserve coffees. To improve the livelihoods of producers through proper conservation of the forests, all coffee types, specifically forest-based coffees, should be harvested at the right ripening stage and processed with the dry method at the recommended moisture content to have the best physical and organoleptic qualities. Since the study focused only on production systems in mid-elevation coffee production systems, the effects of higher and lower elevations and the effects of soil quality on the quality of coffee were not studied. Hence, it is commendable to include the factors that identify variability within the quality of Kafa Biosphere coffees.
For their contributions to this study, we would like to thank colleagues from the Bonga Agricultural Research Center, the Nature and Biodiversity Conservation Union (NABU), the Kaffa Zone Agriculture Office, and Horticoop Ethiopia staff. In person, I would want to express my deepest gratitude to Agidew Bekele (Ph.D.) for his patience and cooperation.
Addis Alemayehu: Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Writing – original draft; Writing – review & editing. Gezahegn Berecha Yadessa: Conceptualization; Methodology; Writing – review & editing. Adugna Debela Bote: Conceptualization; Methodology; Writing – review & editing. Taye Kufa Obso: Conceptualization; Methodology; Writing – review & editing.
CONFLICT OF INTEREST
The authors declare no conflict of interest.
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