Design, fabrication and evaluation of small-scale disc and drum pulpers for Arabica (Coffea arabica L.) and Robusta (Coffea canephora L.) coffee

Abstract

This study describes small-scale drum and disc pulpers developed to depulp Arabica and Robusta cherries in line with Benin and Rwandan farmers' needs. The purpose of the machines is to improve the uncontrolled conventional depulping means, which have led to a decline in parchments quality and can discourage coffee farmers. The development of the machines started with the identification of coffee depulping requirements, followed by analytical sizing of the major components, modeling, fabrication and finally testing. The fabricated machines using local material consist mainly of a hopper, depulping unit, discharge outlet, transmission system and a diesel engine, all supported by a rigid frame. The performance parameters of the machines evaluated with three replications of 3 kg for each variety and depulping clearance of 16 and 12 mm for Arabica and Robusta, respectively at 1200 rpm were analysed in GraphPad Prism V10.0.3. The t-test results of the drum pulper showed a mean pulping efficiency of 98.37 ± 0.73 and 85.00 ± 3.81 %, a capacity of 872.3 ± 91.05 and 924.1 ± 108.3 kg/h, a breakage rate of 0.91 ± 0.27 and 0.00 ± 0.00 %, a pulping index of 0.95 ± 0.01 and 0.70 ± 0.07 and a fuel consumption rate of 1.22 ± 0.54 and 0.86 ± 0.072 l/h for Arabica and Robusta, respectively. Whereas, the disc pulper showed a mean pulping efficiency of 75.56 and 87.5 ± 5.63 %, a capacity of 684.4 ± 215.9 and 756.80 ± 91.54 kg/h, a breakage rate of 0.15 ± 0.26 and 0.00 ± 0.00 %, a pulping index of 0.50 ± 0.14 and 0.79 ± 0.89 and a fuel consumption rate of 0.71 ± 0.30 and 0.73 ± 0.16 l/h for Arabica and Robusta, respectively. The drum pulper outperformed the disc pulper considering efficiency, the pulping index, and the mass of unpulped cherries. The performances revealed that smallholders could prefer both machines based on their settings for each coffee variety.