Vol. 14(6), pp.

213-230, June 2020

DOI: 10.5897/AJPS2020.1976
Article Number: 6EF525464066
ISSN 1996-0824
Copyright © 2020
Author(s) retain the copyright of this article African Journal of Plant Science
http://www.academicjournals.org/AJPS

Full Length Research Paper

The major factors influencing coffee quality in Ethiopia:

The case of wild Arabica coffee (Coffea arabica L.) from
its natural habitat of southwest and southeast
afromontane rainforests
Abebe Yadessa1,2,4,5*, Juergen Burkhardt2, Endashaw Bekele3, Kitessa Hundera4 and
Heiner Goldbach2
1
Center for Development Studies, University of Bonn, Walter-Flex-Str. 3, D-53113, Bonn, Germany.
2
Institute of Plant Nutrition, University of Bonn, Karlrobert-Kreiten-Str. 13, D-53115, Bonn, Germany.
3
College of Natural and Computational Sciences, Addis Ababa University, P. O. Box 28513, Addis Ababa, Ethiopia.
4
Department of Horticulture and Plant Sciences, Jimma University, P. O. Box 307, Jimma, Ethiopia.
5
College of Agriculture and Natural Resources, Wollega University, P. O. Box 395, Nekemte, Ethiopia.
Received 17 February, 2020; Accepted 4 April, 2020

Coffee quality is a complex trait involving sensory and bean characteristics as well as biochemical
contents. The objective of this study was to assess the major factors influencing the quality of wild
Arabica coffee (Coffea arabica L.) in the natural coffee forests of southwest and southeast Ethiopia.
Results revealed that both natural (soil, aspect, elevation, climate, geographic location) and human
factors (cherry harvesting/ handing, theft, forest management) considerably influenced the quality of
wild Arabica coffee. The soil factor affected every component of coffee quality (cup quality, bean
characteristics and biochemical contents). The cup quality of coffee varied with soil properties,
especially with available P and soil texture. The bean size distribution was also affected by soil
properties; there was significant positive relationship between soil pH, sand or Mn and the proportion
of bold beans (retained on screen 17). Soil organic matter, total N and sand content were inversely
correlated with caffeine content, but available P and clay content were positively correlated with
caffeine. Increase in elevation led to increase in bean size up to the elevation of about 1600 m above
sea level, but thereafter no more increase in bean size (hump-shaped relationship, not monotonic).
Bean size increased with increase in longitude, but it decreased with increase in latitude. Cup quality
was also significantly influenced by coffee harvesting and handling, but its influence was not noticed
on bean size and biochemical contents. Coffee quality is therefore the resultant of an interaction of
different natural and human factors prevailing in the respective area.

Key words: Arabica coffee, bean size, biochemical content, cup quality, environment, management/handling.

INTRODUCTION

Food quality is an important feature because the food is fitness for a purpose. Quality refers to the degree of
people choose depends largely on its quality (Vaclavik excellence of a food and includes all the characteristics of
and Christian, 2008). According to Caplan (1978), quality a food that are significant and that make the food
214 Afr. J. Plant Sci.

acceptable (Vaclavik and Christian, 2008). The Wintgens, 2004a, b; Avelino et al., 2005; da Silva et al.,
International Organization for Standardization (ISO) 2005; Knopp et al., 2006; Läderach et al., 2006; Leroy et
defines quality as ‘the ability of a set of inherent al., 2006; Läderach, 2007; Yadessa et al., 2008a;
characteristics of a product, system or process to fulfill Barbosa et al., 2012). And these factors vary from
requirement of customers and other interested parties’ country to country and from place to place, and hence
(ISO, 2000). According to Lochner and Mater (1990), contributing to the quality variations in coffees around the
quality is a measure of the extent to which customer world. Coffee quality is therefore the result of an
requirements and expectations are satisfied. Fisken interaction of these natural and human factors. Although
(1990) defined it as ‘quality is a fuzzy and relative term Ethiopia is the birthplace of Arabica coffee, factors
and it is in a constant motion’. The quality of a product is influencing coffee quality are less studied in the country
not absolute; it always depends upon the requirements of as compared to other Arabica coffee producing countries.
the consumer (Hay and Porter, 2006). Thus, method or Since the country is the source of gene pool for Arabica
group of methods designed to control the quality of a coffee, it would have been the source of Arabica coffee
defined product may be applicable in a particular research information in general and its quality in
situation, but they are subject to a constant evolution particular. Thus, to grow and produce good quality coffee,
(Costell, 2002). This means quality is a subjective term, species/variety, important environmental factors,
and it can have different meanings depending upon the management factors, socio-economic factors, etc. that
context in which the term is used. affect coffee quality should be taken into account.It is
According to Feria-Morales (2002), the quality of green hypothesized that the major factors that affect the quality
coffee mostly depends on the way in which the coffee is of wild Arabica coffee (Coffea arabica L.) from the natural
grown, harvested and processed. Therefore, coffee coffee forest ecosystems are distinct since these natural
quality is hard to define and agree on as the definition of coffee forests are the origin of Arabica coffee and found
quality varies for different stakeholders across the only in Ethiopia (not in other countries like Brazil,
commodity (production-to-consumer) chain. This means Vietnam, Colombia, etc.).Ethiopia has a unique position
what one stakeholder perceives as quality may not be so regarding Arabica coffee world as it is the birthplace or
thought of by another. At the farmer level, coffee quality origin of C. arabica, and the natural conditions for coffee
is a combination of production level, price and ease of growing are almost ideal in Ethiopia (Krug and de Poerck,
culture; at the exporter or importer level, coffee quality is 1968). The objective of the present study was thus to
linked to bean size, lack of defects, regularity of assess the major factors (both natural and human)
provisioning, tonnage available, physical characteristics influencing the quality of wild Arabica coffee (C. arabica
and price; at the roaster level, coffee quality depends on L.) in the natural coffee forests of southwest and
moisture content, stability of the characteristics, origin, southeast Ethiopia, and then to identify the key factors
price, biochemical compounds and organoleptic quality; important for coffee quality.
at the consumer level, coffee quality deals with price,
taste and flavour, effects on health and alertness,
MATERIALS AND METHODS
geographical origin, environmental and sociological
aspects such as organic coffee, fair trade, shade coffee, Study sites
etc. (Feria-Morales, 2002; Leroy et al., 2006; Perriot et
al., 2006). It is a joint effort by all the key players of the The study was conducted in the southwest (Berhane-Kontir, Bonga
coffee production-to-consumer chain (Prodolliet, 2004). and Yayu) and the southeast (Harenna) natural coffee forest
According to Neilson (2007), quality is embodied not only ecosystems of Ethiopia, geographically separated by the Great
RiftValley System. The sites were selected for their landscape
in taste and/or physical attributes, but also through a diversity so as to study the effects of various environmental factors
plethora of social, environmental, ethical, safety and on coffee quality in these ecologically diverse natural coffee forest
other concerns. Thus, quality is a key link between ecosystems. Sheko, Bonga and Yayu are located west of the Great
different stakeholders in the coffee sector, and hence Rift Valley System, whereas Harenna is located east of the Great
coffee quality assessment is an important step in coffee Rift Valley System (Figure 1).
The Yayu Natural Coffee Forest is located in the Yayo District,
trade (Gichimu et al., 2012).
Illubabor Zone of Oromia Regional State in the southwest Ethiopia.
It is generally accepted that coffee quality depends on Yayu has got its name from the word Yayo, the name of the Oromo
different factors, such as the species/varieties, the sub-clan living in the Illubabor Zone. The soils of the area are red or
environmental conditions (soil, rainfall, elevation, slope brownish Ferrisols derived from volcanic parent material (Tafesse,
aspect, etc.), geographic locations (latitude, longitude), 1996). The total annual rainfall is about 1900 mm with mean
methods of processing, etc. (Decazy et al., 2003; temperature of 19.7°C (minimum temperature 7.6°C, maximum

*Corresponding author. E-mail: ay.tarfa@yahoo.com.

Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution
License 4.0 International License
 Yadessa et al. 215

Figure 1. A map of Ethiopia showing the geographical location of the study sites.

temperature 34.7°C) and relative humidity of 80.9% (Kufa, 2006). Sampling procedures and coffee cherry sampling
The Berhane-Kontir Natural Coffee Forest is also called Sheko
forest. It is located in the Sheko District, Bench-Maji zone in the During site selection, preliminary information from the local people
South Nations, Nationalities and Peoples Regional State, and and key informants was collected to assess their perceptions on
hence the name Sheko forest. It represents the transition between what factors might affect coffee quality. To assess the influence of
the Afromontane moist forest and the lowland dry forest, located environmental factors on coffee quality, coffee cherries were
west of the Great Rift Valley (Senbeta, 2006). The total annual sampled from different plots located at different elevation ranges
rainfall is about 2100 mm with mean temperature of 20.3°C and geographic locations. Depending on the nature of the study
(minimum temperature 13.8°C, maximum temperature 31.4°C) and site, the existing slope aspects, including valley bottoms or flat plots
relative humidity of 68.9% (Kufa, 2006). were also included in the sampling as described in Avelino et al.
The Bonga Natural Coffee Forest is located in Kaffa Zone of the (2005). Transects were laid out systematically along the
Southern Nations, Nationalities and Peoples Regional State topographic aspects of the study coffee forest sites. Forty one
(SNNPRS) in the southwest Ethiopia. Bonga has got its name from samples from Berhane-Kontir, 19 from Bonga, 34 from Yayu and 20
Bonga, the king of Kaffa Kingdom. Nitisols are the most dominant from Harenna were studied. Coffee cherries were sampled from the
soils in southwestern Ethiopia, prevailing mainly in coffee and tea respective plots. Elevation and geographic locations (latitude and
growing areas such as the Bonga region (Schmitt, 2006). The total longitude) were measured per plot. Garmin GPS was used for
annual rainfall is about 1700 mm with mean temperature of 18.2°C measuring geographic coordinates and elevation above sea level.
(minimum value of 8.7°C, maximum value of 29.9°C) and relative
humidity of 80.4% (Kufa, 2006).
The Harenna Natural Coffee Forest is located in Bale Zone of the Coffee cherry harvesting, processing and cup tasting
Oromia Regional State in the south-eastern part of the country. It is
a part of Bale Mountains, and the Bale Mountains include the Cherries were harvested at full maturity, which is usually during
northern plains, bush and woods, the Sannate Plateau, and the peak harvesting period. Coffee cherries mature and were harvested
southern Harenna forest. The area is known for its floral and faunal first in Berhane-Kontir (Sheko), followed by Bonga and Harenna,
diversity and endemicity (Friis, 1986; Hillan, 1988). It is located east and lastly in Yayu according to their maturity order in the field. Red
of the Great Rift Valley. The total annual rainfall is about 950 mm cherries were hand-picked from the coffee trees in the coffee forest
with mean temperature of 22.2°C (minimum temperature 10.4°C, and all the samples were then dry processed. The dried cherries
maximum temperature 34.4°C) and relative humidity of 63.2% were manually depulped and the beans were made ready for
(Kufa, 2006). different analyses. Bean size distribution of wild Arabica coffee was
216 Afr. J. Plant Sci.

determined by conventional screen analysis, as described in Feria- RESULTS AND DISCUSSION

Morales (2002) and Wintgens (2004a).Weight fractions retained on
each sieve were recorded as described in Muschler (2001), and
then converted into percentage basis. Cup tasting was conducted
The present study clearly demonstrated that the quality of
at the Coffee Quality Inspection and Auction Center in Addis wild Arabica coffee was considerably influenced by the
Ababa, Ethiopia by a panel of 5 experienced cup tasters (three from environmental conditions and anthropogenic factors
Ethiopia and two from Germany). The major coffee quality attributes prevailing in the natural coffee forest ecosystems from
(fragrance, aroma, acidity, body, flavour, aftertaste and overall where the samples were collected.
quality) were assessed using the beverage quality denominations
ranging from 1 to 10, corresponding to the total absence (or
presence) of the criterion in the coffee samples, respectively. The Influence of soil characteristics
tasters first assessed the fragrance (dry aroma) by smelling the
coffee powder before adding the hot water. After the coffee powder Results revealed that there were significant relationships
has been infused in hot water, the wet aroma of the brew was
assessed. And next the resulting foam was removed before tasting
between soil properties and coffee quality traits. The cup
started and then after the tasters assessed the acidity, flavour, quality of wild Arabica coffee was considerably influenced
body, aftertaste and finally the overall quality. by soil properties, especially by available P (positive
relationship) and soil texture (positive relationship with
fine particles, but negative relationship with sand) (Table
Soil sampling and analysis 1). This means higher levels of soil available P and clay
or silt were associated with better cup quality, and vice
Soil samples (0-20 cm) were collected from each plot. Five samples versa. The probable reason for better cup quality of
were collected per plot and then bulked to obtain a composite
sample, and finally one representative sample was taken from the coffee associated with higher available P concentration of
bulk per plot as described in Yadessa et al. (2001, 2009). Soil the soil might be due to the fact that phosphorus is vital to
samples were analyzed for chemical and physical properties plant growth and it is involved in several key plant
following the standard procedures at International Livestock functions. Phosphorus is a structural element in nucleic
Research Institute (ILRI), Addis Ababa, Ethiopia. Soil texture was acids (Hawkesford et al., 2012), and it plays an important
determined by the Boucoucos hydrometer method (Day, 1965); soil
pH by pH meter in a 1:2.5 (v/v) soil: water suspension; organic
role in energy storage and transfer in crop plants.
carbon (O.C.) by the wet oxidation method (Walkley and Black, Adenosine diphosphate (ADP) and adenosine
1934); available P following the procedures of Bray and Kurtz triphosphate (ATP) are compounds with high-energy
(1945); and total N by the Kjeldahl method (Jackson, 1958). Cation phosphate groups (Fageria, 2009; Hawkesford et al.,
exchange capacity (CEC) was analyzed after extraction with 1 N 2012), and energy is released when a terminal phosphate
ammonium acetate at pH 7 (ammonium acetate method). Micro- is split from ADP or ATP (Sanchez, 2007). Both flowering
nutrients were extracted following the method of Lindsay and
Norvell (1978), and the concentrations in the extract were
and fruiting are reduced by P deficiency (Pallardy, 2008),
determined using atomic absorption photometer. and thus available P is a very important soil nutrient for
cup quality of coffee.Seed quality improves with P
nutrition (Roy et al., 2006), which is in agreement with the
Data analysis findings of the present study. A similar trend was
previously reported by Yadessa et al. (2008a) for Sheko
Multivariate method (redundancy analysis) was used to assess the
relationships between coffee quality traits and environmental and Yayu sites (n=74). Nutrient concentration of the soil
variables. This is because correlation and regression analysis alone and that of coffee leaves in the study sites are presented
may not be suitable when large numbers of variables are involved, in Appendix Tables 1 and 2, respectively.
and thus different methods should be integrated for comprehensive According to the present findings, bean size distribution
analysis (Liebhold and Gurevitch, 2002; Zhang and Oxley, 1994). was also influenced by soil characteristics of the coffee
Multivariate analysis provides statistical methods for study of the
joint relationships of variables (James and McCulloch, 1990).
plots, especially soil pH, Mn, organic matter and soil
Moreover, the multivariate approach usually minimizes the problem texture. There was significant positive relationship
of multicollinearity effects since the ordination axes are independent between soil pH or Mn and the proportion of bold beans
(Sokal and Rohlf, 1995), and multivariate analyses are therefore (proportion of beans retained on screen 17). Generally,
widely used to summarize large data sets (with many variables) by higher concentrations of soil organic matter, Mn, pH and
removing the influence of redundant or irrelevant variables in the sand content were associated with higher proportions of
data set (Dray, 2008; Guoqing et al., 2008).
Redundancy analysis (RDA) is a multivariate direct gradient
larger/bolder beans, and vice versa (Figure 2 and
analysis method appropriate where spatial environmental gradients Appendix Table 3). This could be because mineral
are short (Jongman et al., 1987; Lepš and Šmilauer, 2003; van der nutrients are essential for plant growth and development
Wollenberg, 1977). RDA can be best understood as methods for (Roy et al., 2006; Barker and Pilbeam, 2007). The
extending multiple regression that has a single response Y and developing beans normally act as priority sinks for
multiple predictors X (e.g. several environmental predictors), to
assimilates and minerals (Cannell, 1985), which affects
multiple regression involving multiple response variables Y (e.g.,
several species, traits, etc.) and a common matrix of predictors X endosperm development and dry matter accumulation
(Peres-Neto et al., 2006). Ordination analysis was conducted using and this in turn affects bean size and weight.
CANOCO for windows version 4.5 computer program (terBraak and A study by Mintesnot et al. (2015) showed that coffee
Smilauer, 2002). quality attributes increased with increase in the levels of
 Yadessa et al. 217

Table 1. Pearson correlation matrix showing relationships between cup quality traits and soil properties in the four
natural coffee forests of Ethiopia (n=102).

Cup quality traits

Soil parameter
Fragrance Aroma Acidity Flavour Body Aftertaste Overall
OM -0.17 -0.089 0.045 -0.06 -0.072 -0.134 -0.039
Total N -0.168 -0.073 0.076 -0.054 -0.05 -0.103 -0.024
Available P 0.229* 0.284** 0.115 0.257** 0.192 0.301** 0.239*
OC -0.170 -0.089 0.045 -0.06 -0.072 -0.134 -0.039
Na -0.120 -0.021 0.005 -0.008 -0.076 -0.083 -0.065
K 0.117 0.177 0.012 0.054 0.11 0.148 0.103
Ca -0.089 0.085 0.185 0.118 0.105 0.09 0.135
Mg 0.057 0.219* 0.133 0.119 0.117 0.132 0.125
CEC -0.113 0.039 0.127 0.09 0.069 0.037 0.078
pH -0.077 0.127 0.175 0.136 0.052 0.098 0.119
PBS 0.046 0.169 0.121 0.070 0.099 0.113 0.126
Sand -0.297** -0.321** -0.076 -0.216* -0.148 -0.298** -0.192
Silt 0.333** 0.398** 0.189 0.251* 0.219* 0.320** 0.264**
Clay 0.214* 0.203* -0.02 0.149 0.067 0.224* 0.102
Fe -0.054 -0.067 -0.007 -0.024 0.027 -0.033 -0.020
Mn -0.151 -0.007 0.130 0.103 0.014 0.021 0.048
Zn 0.123 0.19 0.029 0.046 -0.001 0.099 0.027
*, ** = correlations are significant at 0.05 and 0.01 level of significance, respectively.

Figure 2. Redundancy analysis (RDA) biplot of bean size distribution versus soil properties; soil versus
bean size (a) and significant soil versus bean size (b). Arrows represent the directions of maximum
variation of the variables; arrows pointing in the same direction indicate a high positive correlation, arrows
crossing at right angles indicate near-zero correlation, whereas arrows pointing in opposite directions
indicate high negative correlation; the location of coffee quality scores near environmental vectors
suggests the environmental affinities of the trait; p=0.002 for Mn, p=0.004 for sand, p=0.012 for pH,
p=0.016 for Na, p=0.018 for available P and p=0.032 for organic matter. Appendix Table 3 shows the
description of screen sizes.

soil Mg, but decreased with the increase in the levels of soils with excessive calcium and potassium produce
soil total N. A study by Kilambo et al. (2015) reported coffees with hard and bitter tasting liquor. A study by
positive correlation between cup quality and some soil Ngugi et al. (2016) showed that Mn and Zn were
parameters (Ca, Mg, and K), and they also reported that important elements in the determination of organoleptic
218 Afr. J. Plant Sci.

Figure 3. RDA biplot showing the relationships between soil properties and
biochemical contents of wild Arabica coffee in the natural coffee forests of Ethiopia.
CGA= chlorogenic acid, TRIG= trigonelline, CAF= caffeine.

cup quality in Robusta coffee. coffee in its natural habitat of southwest and southeast
Results also revealed that the biochemical contents of coffee forests of Ethiopia, as they influenced every
wild Arabica green coffee beans were also influenced by aspect of coffee quality traits (bean physical quality, cup
soil properties. Higher concentrations of soil organic quality and biochemical contents). Thus, soil is a very
matter, total nitrogen and sand content were associated important factor of quality in coffee production. This may
with lower caffeine content; but the higher the clay be because soil property is an output of different soil-
content, the higher the caffeine content. There was a forming factors (topography, climate, parent material,
positive relationship between available P and bean living organisms, time) and hence factors that influence
caffeine content. Trigonelline was inversely correlated soil property most likely influence coffee plant growth and
with most soil parameters. But chlorogenic acid was less hence its quality.
influenced by soil properties (Figure 3). The probable
reason for low caffeine content under P limited
ecosystem or positive correlation of caffeine with Influence of elevation above sea level
available P status of soil and its negative correlation with
nitrogen could be due to nutrient interaction or The effect of elevation much depended on other factors,
antagonism between N and P. In P limited ecosystem, N such as geographic location (latitude, longitude), soil, etc.
uptake is reduced and subsequently N concentration in This is because elevation is an indirect environmental
plant tissue is decreased. The decrease in N gradient (no direct effect on plant physiology), and the
concentration with increasing P limitation may be major variable that changes with elevation is
mediated by a decrease in leaf cytokinin levels (de Groot temperature, which also changes with latitude and
et al., 2003). Cytokinins regulate cell division in shoots longitude (Austin et al., 1984). Increase in elevation led to
and roots and promote movement of nutrients (Taiz and an increase in bean size and soil organic matter up to the
Zeiger, 2002; Hopkins and Hüner, 2009). A study elevation of about 1600 m above sea level, but thereafter
conducted in Brazil by Mazzafera (1999) to investigate no significant increase (that is, hump-shaped relationship,
the influence of mineral nutrition of coffee on its caffeine not monotonic) (Figure 4). This might be attributed to
contents showed that the omission of P induced the decrease in soil organic matter decomposition and
lowest caffeine content. mineralization (organic matter accumulation), which arise
Generally, both physical and chemical properties of the due to decrease in temperature with increasing elevation.
soil were very important factors for the quality of Arabica A study by Alpizar and Bertrand (2004) also showed that
 Yadessa et al. 219

Figure 4. Variability in the proportion of beans retained on screen 17 (bold beans) across the elevation gradients in
the natural coffee forests of Ethiopia.

the higher the elevation, higher the proportion of large elevation in already a highland area and to higher ranges
size beans; and this relation was observed up to an may lead to decrease in temperature below the optimal
elevation of 1400 m above sea level and then started to range for coffee. The optimum temperature for Arabica
decline thereafter. This could be due to reduced nutrient coffee is between 15-24°C year round, and
availability, which is characterized by higher carbon-to- photosynthesis is reduced above these temperatures
nutrient ratios, such as C:N, C:P, etc. (Wilcke et al., 2003, (Willson, 1999; CRI, 2001). And this also leads to
2008). In the present study, C:P and C:N ratios were decrease in decomposition rate and subsequent
significantly higher at higher elevations than at lower accumulation of soil organic matter. Temperature has a
elevations (data not shown). Thus, decreasing nutrient significant impact on coffee trees (Descroix and Snoeck,
availability at higher elevations might be the probable 2004), and it is generally agreed that every 100 m of
reason for decreasing bean size after an elevation elevation corresponds to a decrease in temperature of
gradient of 1600 m. 0.6°C (Wintgens, 2004b; CRI, 2001).
As shown in Figure 5, coffee bean weight was
significantly varied across the elevation ranges, being
highest in the elevation range 1300-1600 m above sea Influence of topographic aspect
level (asl). Values of 100 bean weight varied from 13.53
to 18.79 g (mean 15.62 g) in the elevation range <1300 m The effect of topographic aspect was rather more
asl, from 14.52 to 20.51 g (17.28 g) in the elevation range important than elevation for coffee quality in the natural
1300-1600 m asl, and from 14.43 to 19.57 g (mean 16.47 coffee forests. Generally, beans on the southern and
g) in the elevation range >1600 m asl. western facing aspects were bolder in size as opposed to
As a general trend, bean size showed a hump-shaped those on the northern and eastern aspects (Figure 6).
relationship with elevation; that is, it increased with This could be due to difference in environmental factors,
increase in elevation at low elevation levels, reached a especially soil properties, which is evidenced by higher
peak at intermediate elevation levels, but declined at high soil organic matter and nutrients on the south-and west-
elevation levels. This may be because increase in facing aspects as compared to the north- and east-facing
220 Afr. J. Plant Sci.

Figure 5. Hundred bean weight across the elevation gradient in the natural coffee
forests of Ethiopia; mean values followed by similar letters are not significantly different
by Tukey’s significant test.

aspects. The reason why coffee beans from the south- sites (decrease in latitude), the proportion of larger/bolder
and west-facing aspects are bolder than those from the beans increased, and vice versa. But for the case of
north-and east-facing aspects could be due to variability longitude, the opposite trend was observed. Generally,
in environmental factors like soil characteristics. This samples that were collected from plots with higher
argument was supported by significantly higher soil longitude readings had relatively higher proportions of
organic matter, pH, and nutrients (e.g. Mn, Ca, Na, etc.) larger/bolder beans. This means the proportion of larger
on the south-and west-facing aspects as compared to the beans decreased from east-west gradient (decrease in
north- and east-facing aspects, as shown in Figure 7. Soil longitude).
Mn (important soil parameter for bean size) was 339.07, In general, the proportion of bold beans decreased as
258.29, 251.12 and 84.07 ppm, under west, south, east latitude increased, but it increased as longitude
and north facing aspects, respectively. A study in China increases, and vice versa. The relationship is shown as
also revealed that high fertility plots often exist on south- follows:
facing slopes and soil organic matter is an important
indicator to soil fertility (Fu et al., 2004). Variation in The proportion of bold beans (% of beans retained on
coffee quality with respect slope aspect may be related to screen 17) = -3.042 latitude readings (in decimal
differences in availability of light, moisture, etc. Slopes degrees) + 3.064 longitude readings (in decimal degrees)
facing the equator (south-facing slopes in the northern – 69.788
hemisphere and north-facing slopes in the southern
hemisphere) receive more radiation than opposing slopes From geographical location point of view, coffee beans
and thus have warmer and drier conditions (Chapin et al., from the SE Afromontane rainforests were bolder in size
2002). A study by Avelino et al. (2005) in Costa Rica as compared to those from the SW Afromontane
showed that coffees from east-facing slopes had better rainforests. This is because soil organic matter, pH, Mn
quality. and sand in the SE were higher than in the SW, and also
their distribution followed an increasing trend along the
west-east longitudinal gradient in the study sites. This
Influence of geographical location variation in soil characteristics imparts variability in coffee
quality. The soils in the southeast are more sandy and
Latitude was inversely correlated with bean size; that is, less weathered (Yimer et al., 2006) compared to the
as one moves from north-south gradient within the study more clay dominated and highly weathered soils in the
 Yadessa et al. 221

Figure 6. Bean size distribution as influenced by topographic aspect in the natural coffee forests of
Ethiopia.

Figure 7. Soil pH and Mn concentrations across the different topographic aspects in the Afromontane
rainforests of Ethiopia.

southwest (Dubale and Mikiru, 1994). As latitude near the poles. At the equator, the sun’s rays are almost
increases, temperature decreases. Latitude influences perpendicular to the surface at solar noon. At lower sun
the climate by influencing the amount of solar radiation angles experienced at high latitudes, the sun’s rays are
received (MacMahon et al., 2007). Areas near the spread over a larger surface area, resulting in less
equator receive more incoming solar radiation than areas radiation received per unit ground area (Chapin et al.,
222 Afr. J. Plant Sci.

Table 2. Pearson correlation coefficients showing the relationship between climate and coffee
quality traits; climatic data from mobile weather station was used.

Traits Rainfall Tmin Tmax

Sensory characteristics
Fragrance 0.227* 0.348** -0.267**
Aroma 0.116 0.262** -0.100
Acidity -0.071 0.024 0.103
Flavor -0.009 0.135 0.028
Body 0.071 0.158 -0.032
Aftertaste 0.093 0.234* -0.091

Bean charactersitics
+
Screen 18 -0.077 -0.091 0.175
Screen 17 -0.584** -0.446** 0.623**
Screen 16 -0.240* -0.144 0.186
Screen 15 0.484* 0.365* -0.559**
Screen 14 0.527** 0.406** -0.533**
-
Screen 14 0.475** 0.335** -0.460**
100 bean weight -0.404** -0.421** 0.502**
Bean length -0.361** -0.397** 0.309**
Bean width -0.080 0.046 0.254**
Bean thichness 0.109 0.015 -0.085
Bean shape index -0.313** -0.385** 0.207*
Tmin = minimum temperature, Tmax = maximum temperature.

2002; Raven et al., 2010). For each degree of latitude development of beverage quality (da Silva et al., 2005). A
away from the equator, the corresponding reduction in study by Camargo et al. (1992), cited in da Silva et al.
temperature is estimated at 0.5 °C (Descroix and (2005) also suggested that regions with a relatively high
Wintgens, 2004). temperature tend to produce low quality coffee.

Influence of climate Influence of forest management on coffee quality

There was a positive and significant relationship between Anthropogenic factors (human activities) are one of the
minimum temperature and coffee aroma (Table 2). This causes for spatial heterogeneity of ecosystems.
may be because climate is an important factor with According to the present study, the level of forest
considerable effect on soil properties and thus important management influenced both the cup quality and the
factor for coffee quality. It affects the rate of soil formation bean physical characteristics of wild Arabica coffee, but
especially temperature and rainfall and the type of soil not the biochemical contents. The level of forest
that is ultimately formed by influencing weathering management (level of human interference) considerably
processes. influenced the bean size distribution and cup quality
The climate also affects the type of vegetation it traits. When the level of human interference was
supports by influencing the physiology of plants such as relatively higher, the cup quality of coffee was better, the
photosynthesis, flowering, maturity, etc., which has proportion of larger beans increased, and available
implications on coffee quality. This is very interesting in phosphorus increased but soil organic matter decreased.
the context of current global climate change. The ‘Managed (slashed) plots had relatively better cup quality
influence of rainfall on cup quality was not as apparent as and higher proportion of larger beans. This could be due
that of its effect on bean size distribution. In general, the to improved micro-environmental conditions such as
higher the rainfall, the higher the proportion of smaller light/temperature and subsequent decomposition and soil
beans and vice versa (Table 2). High temperature mineralization and reduction of weed competition (Table
accelerates fruit maturation in coffee (Descroix and 3).
Snoeck, 2004). But at lower temperature coffee fruits Forest coffee management modifies the forest
undergo a slower maturation process, allowing the full ecosystem by changing the microclimate (e.g. light, soil,
manifestation of all biochemical steps necessary for the etc.) and the forest conditions (e.g. species composition,
 Yadessa et al. 223

Table 3. Cup quality and bean size distribution of wild Arabica coffee as influenced by forest management in the natural coffee forests of
Ethiopia.

Cup quality traits

Level of forest management
Fragrance Aroma Acidity Flavour Body Aftertaste Overall
b b b b b b
Little 5.54 5.22 5.48 4.75 5.53 4.64 5.20
ab a a a a a
Medium 5.93 5.79 6.00 5.58 6.04 5.37 6.02
a a ab a a a
High 6.09 5.94 5.96 5.51 6.06 5.33 5.96
P value 0.025 0.013 0.049 0.003 NS 0.018 0.004

Bean size distribution (%)

Screen 18+ Screen 17 Screen 16 Screen 15 Screen14 Screen 14-
b b a
Little 5.12 17.31 32.93 24.45 12.65 7.56
b ab a
Medium 5.62 17.81 32.56 23.47 13.21 7.34
a a b
High 9.40 23.03 30.72 19.61 11.14 6.11
P value 0.000 0.028 NS 0.005 NS NS
Means followed by similar letters are not significantly different by Tukey’s significant test.

Figure 8. Theft affects coffee quality by affecting cherry harvesting quality.

Source: Photo by Abebe Yadessa.

vegetation structure, space availability, etc.), due to tree the problem of cherry thievery in the field during
thinning and slashing of undergrowth (Senbeta and harvesting, farmers in some coffee growing areas are
Denich, 2006; Hundera et al., 2013). Forest management forced to pick green and red cherries together (that is,
also influences soil nutrient ratios, which impart variations early harvest) as an escape strategy, and this has a
in coffee quality (Yadessa et al., 2019). But in contrast to considerable impact on coffee quality (Figure 8a, b).
the present findings, a study by Geeraert et al. (2019) Harvesting quality is essential for better cup quality of
reported a decreasing trend in cup quality of Arabica coffee (Perroit et al., 2006). The problem of coffee cherry
coffee with increasing intensity of coffee forest theft during harvesting is also reported by Schmitt (2006),
management. which is in agreement with the present findings. But this
forced early harvest due to thievery should not be
confused with the early harvest of red cherries, which
Other important factors affecting coffee quality may give even better cup quality. For instance, Läderach
(2007) reported relatively better beverage quality for early
Theft problem harvest as compared to late harvest. Unintentional or
intentional harvesting of cherries at several stages of
The effect of theft on coffee quality is indirect. Because of maturation may have adverse impacts on coffee quality if
224 Afr. J. Plant Sci.

Figure 9. Selected cup quality traits of wild Arabica coffee collected from below the trees as compared to hand-picked
coffees in Sheko coffee forest site. Sheko-above refers to coffee samples from farmers but collected from the coffee
trees (not from the ground), whereas Sheko-below refers to coffee samples from farmers with coffees collected from
below the trees (fallen berries from the ground floor).

these materials are processed together (Brando, 2004). picking of fallen cherries from the ground are the major
Thus, coffee quality, especially its cup quality is directly harvesting-related factors influencing coffee quality in the
correlated with optimal cherry maturity, and theft thus study sites.
plays a considerable role in coffee quality by influencing
cherry harvesting quality.
Lack of differential price for coffees of different
quality
Heavy rainfall during peak harvesting period
Traders usually pay the same price for coffees of different
Rainfall influences coffee quality in both direct and quality, and bulking of coffees of different qualities or
indirect ways. On one hand, heavy rainfall can lead to origins is not uncommon practice in the study areas and
falling (drop) of cherries from coffee trees to the ground elsewhere as well with no consideration for quality
before harvest. Fallen cherries from the ground (below harvesting and processing (Figure 10). And payment is
coffee trees) can be a major constraint to coffee quality effected on the basis of quantity, not on quality; that is,
unless care is taken (Figure 9). On the other hand, heavy there is no market segmentation according to coffee
rainfall during harvesting and/or processing can lead to quality. This inevitably leads to reluctance by producers
mould development due to inappropriate drying. Coffee for the coffee quality if this problem is not taken into
quality is highly dependent on post-harvest processing consideration in the future. This is almost common in
(Menon, 1992; Perroit et al., 2006). Because of heavy most of the study sites or elsewhere. A study by Kodama
rainfall during cherry maturity or during post-harvest (2007) also showed that farmers sell a better quality
processing, coffee cherries and/or beans can be coffee to cooperatives as they expect dividends, but they
contaminated by soil when dropped to the ground giving are less concerned about the quality of coffee for private
earthy or moldy taste. A study by Tagliaferro et al. (2007) traders. A study in Jimma zone by Tolessa et al. (2018)
also showed that the impurities from the soil can reach revealed that coffee beans managed by cooperatives had
the cup and spoil the beverage quality, and this supports better quality scores than those managed by private
the present findings. Falling of cherries from the coffee traders. A study by Bacha (2007) in Bonga (Kaffa zone),
trees to the ground due to heavy rainfall was more for instance, showed that the share of forest coffee
apparent in Sheko area as compared to other forest producers is only 3% of the retail price.
coffee sites, due to heavy rainfall and local tradition of The lack of differential price has two negative effects,
cherry handling prevalent in the area. Therefore, namely: (i) discourages farmers to invest in coffee quality
harvesting of green cherries, over-ripe cherries, and improvement (resources like money, labor, time, etc.),
 Yadessa et al. 225

Figure 10. Coffees of different quality, but sold with the same price; (a) well dried coffee, and (b) mould
developed coffee.
Source: Photo by Abebe Yadessa.

better quality scores than those managed by private sources, from forest or plantation, red or green
traders. A study by Bacha (2007) in Bonga (Kaffa zone), harvested, well dried or mould developed, etc., are sold
for instance, showed that the share of forest coffee with the same price. There is usually little or no market
producers is only 3% of the retail price. differentiation, if any, for coffees of different quality, which
The lack of differential price has two negative effects, leads to reluctance of farmers to give more attention to
namely: (i) discourages farmers to invest in coffee quality quality. High quality coffee requires special care and thus
improvement (resources like money, labor, time, etc.), coffees with better quality represents good differentials of
and (ii) bulking of coffees of different quality (sources) product price (Pereira et al., 2010).
considerably influences coffee quality. Generally, if there
is no or little difference in the price of a high and a low
quality coffee, farmers will show reluctance for investing Limited research capacity
in coffee quality improvement activities because such
investment cannot justify the incurred cost. Although Ethiopia is the birthplace of Arabica coffee,
factors influencing coffee quality are less studied in the
country as compared to other Arabica coffee producing
Poor share-harvesting arrangements countries. Limited trained manpower and institutional
capacity are the major bottlenecks in the country. But this
The use of hired labour from the neighbouring non-coffee is not the case at the present time, and this should be
growing areas (e.g. Adaba, Ganale, Bidire, etc.) is also given due attention in the future.
an important factor of coffee quality since payment for
labourers is based on the quantity harvested, not on the
quality of coffee harvested. One third of the harvest is Poor cooperation between the coffee stakeholders in
usually for the collector and two third is for the owner, quality control
without due consideration to the quality of cherry
harvested. This problem is more common in Harenna Collectors/traders in most cases buy coffees without due
area (Yadessa et al., 2008b). It is also a problem in consideration to quality, no differential price for different
Sheko area. quality coffees. They also buy coffees from anybody,
including thieves. In the case of cooperatives, on-farm
supervision is a common practice, and production,
Bulking of coffees from different sources harvesting and processing are usually supervised with
the technical staff of the cooperatives. They also
In many coffee producing areas, coffees from different participate in development works such as schools, clinics,
226 Afr. J. Plant Sci.

Figure 11. Schematic presentation of the major factors influencing coffee quality and their interactions in Ethiopia.

feeder roads, etc. But in the case of traders, participation other. Therefore, the role of agricultural marketing
in development activities are less experienced. But cooperatives is very crucial for smallholder farmers.
traders in some cases slightly increase some cents for
coffee price to relieve from the competition with
cooperatives or farmers, but still these are not as such Poverty and illiteracy
significant. Apart from the price, handling coffee lots from
different sources or farmers differently is not an easy task Apart from the above factors, one of the main challenges
as well, which is one constraint for coffee quality facing small-scale coffee producers is their lack of access
improvement. to physical, economic, and educational resources. Many
In Ethiopia, coffee cooperatives have brought benefits farmers lack the knowledge and resources (financial or
to coffee farmers by providing a new marketing channel. material) to ensure efficient and high quality coffee
The dividends are being appreciated by farmers and production. Moreover, traders or suppliers should also be
have encouraged farmers to improve the quality of their experts in coffee quality themselves to alleviate these
coffees. Although the actual volume purchased by problems. Another problem is that those who have
cooperatives is limited due to financial constraints, the information often lack the resources for quality
existence of cooperatives in the coffee market has improvement (ITC. 2011a).
improved the purchasing price offered by private traders In general, coffee quality is the result of interaction of
because of competition with the cooperatives. Since the both natural/environmental (soil, climate, elevation,
late 1990s, in Ethiopia cooperative activities have been aspect, latitude, longitude) and human (coffee
encouraged again, despite bad experiences during the management, theft, harvesting, processing) factors, as
socialist regime (Kodama, 2007). Cooperatives are being summarized in Figure 11. For any system to function
appreciated or recognized as business and marketing properly, there are naturally interactions between the
organization in Ethiopia and as one means of protecting different components of the system. One element of the
farmers as opposed to its past notion. This is because, in system can’t exist on its own (Yadessa et al., 1999).
union there is strength. Thus, different stakeholders in Similarly, there is an inevitable interdependence and
coffee sector better promote quality and the sustainability interrelationships among the different factors affecting
of coffee production rather than competing with each coffee quality in one way or another. As presented in
 Yadessa et al. 227

As presented in Figure 11, different factors affect coffee the nucleus or focus of the current study.
quality:

i) Environmental factors (soil, topography, climate, CONFLICT OF INTERESTS

geography),
ii) Management factors (cherry harvesting and The authors have not declared any conflict of interests.
processing, slashing/forest management),
iii) Socio-economic factors (theft problem, poor-share
arrangement, lack of differential price, poverty and ACKNOWLEDGEMENTs
illiteracy etc.),
iv) Institutional factors (cooperatives, traders, etc.). The authors appreciate the Center for Development
Research (ZEF), University of Bonn, and Environment
As to the genetic factors, the study was conducted in and Coffee Forum (ECFF) for supporting the research
natural coffee forest ecosystem (the gene pool for other activities; Forestry Research Center and Jimma
Arabica coffee varieties) and Robusta coffee is not Agricultural Research Center for provision of vehicles and
common in Ethiopia, and hence the issue of coffee other assistances; Ethiopian Institute of Agricultural
species/variety in natural coffee forests harbouring wild Research, Addis Ababa University, Jimma University,
coffee Arabica populations is less relevant here. Of Wollega University, Robera Coffee PLC, Oromia Coffee
course, the genetic factor might have contributed to the Cooperatives Union, and Ethiopian Coffee Quality
quality of wild Arabica coffee in its natural habitat of Inspection and Auction Center (CLU) for their assistance
southwest and southeast Afromontane rainforests of and cooperation; the panel of cup tasters for their
Ethiopia, but further study on genotype and environment participation in the cup tasting, and farmers, traders and
(G*E) interaction is required. development agents for their assistance during soil and
As the importance of quality and origin is increasing in coffee samples collection. The research was sponsored
coffee market, the research that deals with factors that by German Federal Ministry of Education and Research
influence coffee quality should be a priority in coffee (BMBF).
research. Generally, high-quality coffee arises from
maintaining close control over a multitude of factors in the
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230 Afr. J. Plant Sci.

APPENDIX

Table 1. Mean values (±standard deviation) for the considered soil parameters from the four Afromontane rainforests in the
SW and SE Ethiopia.

SW soils SE soils
Statistic
B. Kontir (n=41) Bonga (n=16) Yayu (n=34) Harenna (n=20) P value
c b b a
SOM (% DM) 4.64±1.34 6.52±1.25 7.21±2.20 8.49±1.00 0.000
c b b a
Total N (% DM 0.32±0.07 0.41±0.05 0.41±0.13 0.52±0.005 0.000
a b b b
Avail. P (ppm) 39.99±34.48 3.44±7.52 11.22±12.56 1.94±2.09 0.000
c b a
Na (meq/100 g) 0.05±0.06 0.10±0.06 0.04±0.02 0.16±0.07 0.000
a a a b
K (meq/100 g) 1.23±0.68 1.34±0.80 1.07±0.74 0.56±0.40 0.002
bc c b a
Ca (meq/100 g) 11.88±4.87 9.40±3.52 13.15±5.74 19.18±3.89 0.000
Mg (meq/100 g) 3.70±1.77 2.91±1.09 3.04±1.56 3.73±0.58 NS
b b b a
CEC (meq/100 g) 29.08±7.39 34.96±5.05 32.22±12.33 43.77±4.69 0.000
a b a a
BS (%) 56.58±12.57 39.01±13.68 53.89±11.83 54.44±10.23 0.000
b c b a
pH 5.90±0.24 5.47±0.43 5.82±0.22 6.42±0.18 0.000
c b a a
Sand (% DM) 20.18±9.07 29.13±6.37 43.82±11.14 46.70±5.92 0.000
a a b b
Silt (% DM) 37.76±4.76 34.57±3.37 28.88±7.76 27.86±2.70 0.000
a b c c
Clay (% DM) 42.06±8.02 36.31±5.49 27.30±4.69 25.44±5.95 0.000
b a b b
Fe (ppm) 57.39±34.98 246.36±313.99 50.93±40.78 82.61±50.44 0.000
ab b b a
Mn (ppm) 136.91±45.96 212.10±158.79 66.29±28.11 738.74±179.06 0.000
a a b ab
Zn (ppm) 2.97±1.72 3.26±01.85 1.41±0.60 2.38±0.55 0.000
Means followed by similar letters within a row are not significantly different, DM = dry matter, BS= base saturation, SOM = soil organic
matter, 1 ppm=mg/L (liquid substance) or 1 mg/kg (solid substance). In terms of percents, 1 ppm equals 0.0001 percent.
Source: Yadessa et al. (2019).

Table 2. Leaf nutrient content in the Afrontane rainforests of southwest and southeast Ethiopia harbouring wild C.
crabica populations.

Nutrient Harenna Bonga Yayu B.-Kontir

c b c a
P (%) 0.07 0.12 0.11 0.15
c b b a
K (%) 1.80 2.2 2.1 2.7
a b c c
Ca (%) 1.60 1.2 0.33 0.02
a b bc ac
Mg (%) 0.35 0.33 0.26 0.28
b b c b
Zn (ppm) 13.9 11.5 9.7 11.1
b b b a
Mn (ppm) 61.0 67 59 98
Means followed by similar letters within a row are not significantly different.
Source: Beining (2007).

Table 3. Screen sizes and descriptions.

Screen no. Screen diameter (mm) ISO norm Bean size description
20 7.94 8.00 Very large
19 7.54 7.50 Extra large
18 7.14 7.10 Large
17 6.75 6.70 Bold
16 6.35 6.30 Good
15 5.95 6.0 Medium
14 5.55 5.6 Small
13 5.16 5.0
12 4.76 4.75
Source: Wintgens (2004b).