Effect of Altitude, Shade, and Processing Methods on the Quality and Biochemical Composition of Green Coffee Beans in Ethiopia

Abstract: There are growing demands for high quality coffee in the international market today. This has
given coffee producing countries an impetus to increase the quality as well as the quantity of coffee they
produce. For improving coffee quality and meet market demands, attention has been given to exploring
genetic and environmental factors as well as agronomic and other coffee management practices.
However, little information is available in Ethiopia regarding effect of environmental factors such as
altitude and coffee management practices such as shading and processing methods on the quality and
biochemical composition of green coffee beans. This problem has constrained efforts being made in the
country to further exploit the growing demands for quality coffees in the international market.
Therefore, a study was conducted during the 2010/11 main cropping season to determine coffee quality
attributes as a function of altitude, shade, and processing methods. Red ripe coffee cherries were
handpicked from three coffee farms in south-western Ethiopia located at altitudes of 1150, 1545 and
1802 meters above sea level, which represented lowland, midland, and highland coffee growing areas,
respectively. The coffee cherries were obtained from both shaded and unshaded farms in each of the
aforementioned coffee growing areas. The green coffee beans were subjected to both wet and dry coffee
processing methods. A total of 36 coded samples (18 washed and 18 unwashed green coffee beans) with
a moisture content of about 10.5% were subjected to cup and laboratory tests. Coffee cup test was done
according to the procedure of Ethiopian Commodity Exchange (ECX) using 36 green coffee bean
samples. Contents of caffeine, trigonelline, and chlorogenic acids were determined using
HPLC/THERMO. Sucrose was determined using GC VARIAN 3800. Univariate analysis of variance
and stepwise multiple regression analyses were conducted using SPSS 16 v2. The results revealed that
coffee beans originating from the high altitude had significantly higher first grade and Q1 grade points
than coffee beans originating from the low and middle altitudes. Unshaded and unwashed coffee grade
was better than the washed and shaded coffee grade. Caffeine content of the beans was affected neither
by altitude, shading, nor by the processing method. Shading affected only the content of bean
caffeoylferuloylquinic acids (CFQA), which was found to be significantly higher for the unshaded coffee
bean samples than the shaded coffee bean samples. Contents of 4,5-dicaffeoylquinic acid (4,5-DCQA),
feruloylquinic acids (FQA), and total chlorogenic acid (TCGA) were significantly higher for coffee beans
originating from the low and middle altitudes than those originating from the high altitude. Similarly,
coffee beans that originated from the low altitude had significantly higher contents of 3,4-
dicaffeoylquinic acid (3,4-DCQA), caffeoylferuloylquinic acids (CFQA), and trigonelline than coffee
beans that originated from the high altitude. However, coffee beans that originated from the high and
middle altitudes had significantly higher contents of chlorogenic acids, i.e., 3-caffeoylquinic (3-CQA) and
5-caffeoylquinic acid (5-CQA) than coffee beans that originated from the low altitude. The sucrose
content of coffee beans that originated from the low latitude was significantly higher than the sucrose
content of coffee beans that originated from middle and high altitudes. Washed coffee beans contained
significantly higher amounts of dicaffeoylquinic acid (4,5-DCQA), caffeoylquinic acid (5-CQA),
chlorogenic acid (TCGA), and trigonelline than unwashed coffee beans. However, unwashed coffee
beans had significantly higher 3-caffeoylquinic (3-CQA) and caffeoylferuloylquinic acids (CFQA)
contents than washed coffee beans. Unwashed coffee beans had higher values for primary defect,
secondary defect, odour, total-point and preliminary grade whilst washed coffee beans had better scores
for acidity, body, and flavour attributes, which distinctly influence the ultimate taste profile of coffee
origins. It is concluded that coffee bean quality attributes and contents of the associated chlorogenic
acids improved in response to increased altitude under both shaded and unshaded conditions regardless
of the type of processing method used. The results imply that growing coffee plants in the highlands and
midlands rather than in the lowlands as well as washing the beans results in the production of coffee
beans with high quality attributes and chlorogenic acid contents that could meet the rising international
market demands for high cup quality.