Quality response of robusta coffee (coffea robusta var. canephora) beans to methods and depths of drying.
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Date
2011
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Abstract
Due to the poor quality of coffee beans arising from poor processing methods, studies were conducted at KwahuBepong, with laboratory support at the Cocoa Research Institute of Ghana (CRIG) and the Horticulture Department of KNUST from November, 2010 to March, 2011. The objectives of the studies were to; (I) determine the combined effect of the method of drying and the depth of drying on the coffee cup quality of Robusta coffee beans, (II) determine the effect of the drying process (method and depth) on the incidence and percentage infestation of fungal mould as a determinant of quality. The experimental design was a 3 x 3 factorial arrangement in randomized complete block with three replications. The first factor was methods of drying at three levels - M1:- drying on a raised raffia mat at 0.8 m above ground; M2:- drying on a concrete floor and M3:- drying on a black polythene sheet on concrete floor. The second factor was the depth of drying at three levels - D1:- 5 cm; D2:- 10 cm and D3:- 15 cm. Data collected included number of days to drying, percent caffeine and crude protein contents, temperature and moisture within bean heap, fungal load and defective beans. The number of days to drying, temperature and moisture within heaps, total fungal load and defective beans differed significantly (P < 0.05) with respect to drying methods and depth of drying of the coffee beans. However, the treatments did not have any effect on the caffeine contents. Microbial counts were found in all samples during drying of the coffee beans with Aspergillusspecies being the most prevalent. Generally, beans dried on raised raffia mat dried faster and with less microbial count. There was a significant relationship between percentage crude protein content and temperature within the heap of coffee beans.
The temperature in the heap of coffee beans during drying accounted for 77% of the variation in total crude protein content. The relationship is expressed as Total Crude Protein = 0.891 + 0.098 (Temperature); R2 = 0.77; P = 0.002. The study concluded that drying coffee beans on black polythene sheet on concrete floor at a depth of 5 cm resulted in desirable effects similar to those obtained using the raised raffia mat. The desirable effects included faster drying time and increased crude protein content of beans coupled with lower fungal load contamination. Consequently, in the absence of a raised raffia mat due to the unavailability of its basic materials, the black polythene sheet on concrete floor could be a worthy substitute without compromising on coffee bean quality with its consequent effect on cup quality.
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A thesis submitted to the School of Research and Graduate Studies, Kwame Nkrumah University of Science and Technology, in partial fulfilment of the requirements for the award of Master of Science (Msc. Postharvest Technology) degree