Physico‐mechanical properties of unripe grape berries relevant in the design of juicing machine

Abstract

AbstractTo optimally design post‐harvest handling and processing equipment for unripe green grape berries, it is necessary to determine the physical and mechanical properties of the product. In the current study, dimensional (by image processing), gravimetrical, frictional, and aerodynamic (by image processing) properties of unripe green grape berries affected by storage time (31 days in refrigerator) were investigated. Besides, rupture force, rupture energy, elasticity modulus, toughness, hardness, maximum compressive contact stress, Poisson's ratio (by image processing), and shear modulus in horizontal and vertical loading under different moisture content and loading rate levels were measured. Moreover, to model loading and stress‐relaxation behavior of bulk berries, berries were poured into cylinder and compressed. Effects of cylinder diameter, loading rate, the height of layers, and number of layers on loading and stress‐relaxation behavior were investigated. During storage, as the moisture content decreased from 94.57 to 83.88% (w.b.), dimensions and mass of the berries decreased while bulk density and true density increased. With decreasing the moisture, friction angles on galvanized, iron, and rubber were ranged from 22.43° to 26.73°, from 25.38° to 28.53°, and from 29.7° to 34.2°, respectively. Filling angle of repose ranged from 13.44° to 17.65° and emptying angle of repose ranged from 13.95° to 18.33°. In the mentioned moisture range, terminal velocity increased from 0.202 to 0.275 m s−1, and drag coefficient increased from 0.180 to 0.272. Reducing moisture content and increasing rupture energy of the fruits during storage indicates that berries' juice should be extracted immediately after harvest.Practical ApplicationsUnripe grape berries with a sour taste can be processed into several sour sauce and verjuice products. Therefore, determining the physical properties of unripe grape berries is essential for the design of harvesting and post‐harvesting equipment. The current work aims to determine unripe grape berries' physical and mechanical properties to recognize their relevance in physico‐mechanical processing. Some of the necessary information for designing and manufacturing harvesting and post‐harvesting machines is provided in this research. Thus, the results provided in the present study would contribute to improving juice extractors, sorters, separators, cleaners, storage structures, dryers, aeration equipment, conveyors, pneumatic elevators, and so forth, designed for the unripe grape berries.