Cracking characteristics and kernel extraction quality of hazelnuts: Effects of compression speed and positions

Abstract

Force, energy, and specific deformation required for initial rupture and kernel extraction quality of hazelnuts were investigated as functions of shell thickness and geometric mean diameter at different compression positions (length, width, and thickness) and speeds (0.5, 1.0, 1.5, and 2.0 mm/s). For this purpose, two groups of nuts of hazelnut (Corylus avellana L.) cv. Tombul were compressed with a universal testing machine. The lowest rupture force values were obtained from along the width direction, while nuts compressed at length position had higher quality scores (5.00 and 4.89) compared with other positions in both groups. The force for cracking increased with increasing test speeds, and reached to 214 N at the speed of 2 mm/s in the first group (larger than 16 mm diameter) samples. Less energy was required to crack nuts at the speeds of 0.5 and 1.0 mm/s compared with 1.5 and 2.0 mm/s compression speeds in both sample groups. Generally, rupture force and energy for cracking increased linearly by increasing shell thickness. The energy required to initiate cracking increased as the size of hazelnuts increased for all three axes. Results revealed that there was no relationship between kernel extraction quality and geometric mean diameter. Experimental results from compression tests indicated that cracking nuts at the width position required less force and yielded good kernel extraction quality at the speed lower than 1 mm/s.