Drying Induced Changes in Engineering Properties of Cherry and Parchment Coffee

Abstract

Engineering properties of coffee are important for the efficient design of drying, handling, storage, and processing equipment in post-harvest operations. This study investigated the effect of drying on the physical and frictional properties of arabica and robusta coffee cherries and parchment coffee at the Central Coffee Research Institute, Adigebylu village, Koppa taluk, Chikkamagaluru district, Karnataka, India. Significant variations (P = 0.05) were observed due to coffee species and moisture content. Fresh arabica cherries exhibited larger dimensions, with mean length, width, and thickness values of 15.50 ± 0.05 mm, 13.40 ± 0.42 mm and 11.94 ± 0.09 mm, respectively, compared to robusta cherries. Drying significantly reduced the dimensional characteristics of both coffee species. The volume of arabica cherries decreased from 1338.18 ± 21.01 mm³ to 757.92 ± 121.08 mm³, while robusta cherries showed a reduction from 1059.29 ± 12.09 mm³ to 704.39 ± 73.04 mm³ after drying. Sphericity decreased from 87.35 ± 0.96% to 79.01 ± 3.43%, whereas the shape index increased from 1.23 ± 0.02 to 1.42 ± 0.09 in arabica cherries. Thousand bean weight and bulk density also declined considerably following drying, while porosity increased markedly. Similar trends were observed in parchment coffee samples, where volume decreased from 441.98 ± 12.45 mm³ to 268.36 ± 32.91 mm³. The observed changes in size, density and flow properties indicate the significant influence of moisture reduction on the engineering properties of coffee. These findings provide essential information for the design and optimization of coffee drying, handling, processing, storage, and transportation equipment.