Experimental characterization and finite element modeling of mechanical compression in Coffea arabica fruits from different varieties

Mechanical damage during coffee pulping may affect bean quality, making the characterization of coffee cherry mechanical properties relevant for machine design. This study evaluated the firmness and fracture force of ripe Coffea arabica cherries from Castillo and Colombia varieties as functions of fruit size and compression orientation. A total of 192 cherries were tested by parallel-plate compression using a factorial experimental design and ANOVA. Firmness was determined from the slope of the pre-fracture linear region of the force–displacement curve, whereas fracture force was identified at the onset of structural failure. The mean fracture force was 38.19 ± 19.35 N and increased from 34.78 ± 17.30 N for small fruits to 41.61 ± 20.73 N for large fruits. Fracture force was significantly affected by variety (p = .027), size (p = .011), and compression orientation (p = .027), in both equatorial directions, and polar direction. Mean firmness was 11.52 ± 5.04 N/mm and was significantly influenced only by variety (p = .001). A finite element model reproduced the nonlinear compression tendency and identified stress concentrations along the load-transfer paths toward the seeds. These findings provide quantitative mechanical parameters for coffee pulper calibration and design.