Post-harvest evaluation of Arabica and Robusta coffee for physical, mechanical and aerodynamic properties

Knowledge about physicomechanical and aerodynamic properties is indispensable for any crop that undergoes post-harvest processing; coffee is no exception. These properties are the most crucial parameters for designing and developing processing machinery and storage structure. As far as coffee is concerned, these properties are imperative for designing dryers, hullers, peeler-cum-polisher and size graders. Though coffee is one of the leading plantation crops in India, published reports on physical, mechanical and aerodynamic properties are rather limited. In this direction, a study was attempted to generate data in respect of physical (length, width, thickness, volume, surface area, thousand seed weight, bulk density, true density and porosity), mechanical (angle of repose and co-efficient of friction) and aerodynamic (terminal velocity) property in different coffee types (parchment, cherry and clean coffees of both Arabica and Robusta varieties). At the prescribed moisture content of 11 per cent, the length, width, thickness, volume and surface area were significantly higher (p=0.05) in cherry coffee, followed by parchment and clean coffees. The porosity, bulk density and true density were found in the order of 45 to 58 per cent, 395 to 466 kg m-3 and 856 to 944 kg m-3 for cherry, 56 to 57 per cent, 400 to 410 kg m-3, 950 to 966 kg m-3 for parchment and 37.5 to 44 per cent, 691 to 780 kg m-3 and 1,106 to 1,401 kg m-3 for clean coffee, respectively. There were no significant differences between coffee types in respect of angle of repose, co-efficient of friction and terminal velocity. The data generated under this study can be harnessed while configuring or improving the coffee processing machinery and helps achieve the final product with desirable quality characteristics

The effect of drying temperature on cup quality of coffee subjected to mechanical drying

The objective of the work was to study the effect of drying temperature on cup quality of the robusta coffee subjected to mechanical drying in comparison with conventional sun drying. The robusta coffee processed by wet (parchment coffee) and dry (cherry coffee) methods were subjected to drying at different temperature regimes (40 oC, 50 oC and 60 oC) in a rotary mechanical dryer. The results of the study indicated that as the drying temperature increased, the time of drying reduced. Sun drying of parchment coffee took 48 hours (approximately seven days) to attain the desired moisture content of 11-12 per cent, while mechanical drying reduced the drying time to 16 to 24 hours. Similarly, cherry coffee subjected to sun drying took 88 hours (approximately 15 days), while mechanical drying reduced the drying time to 32 to 48 hours. The cup quality rating of coffee dried by different drying methods revealed that sun-dried robusta parchment coffee scored the highest cup rating. As the drying temperature increased, the cup quality ratings decreased. A similar cup quality rating was also observed with cherry coffee. These results indicate a considerable reduction of drying time when coffee beans are dried in a mechanical dryer. However, there is a need to regulate the drying temperature, which otherwise would negatively impact the quality of coffee. The drying temperature should not exceed 40oC for preserving the innate quality of robusta coffee because the high drying rates provoked by high temperatures can cause damage to the coffee quality due to the damage caused to the cell membranes. Overall, mechanical drying is more advantageous to sun drying in-terms of drying hours (indirectly reduces dependency on manpower) and preservation of innate quality of the coffee