Materials and methods
Three di!erent varieties of rice used were Akita-
komachi (short grain), Delta and L201 (long grain). Bio-
yield point, and yield point were determined using
a stress}strain tester by compressing rough rice on a me-
tallic #at surface at 0)14 mms~1. A computer simulta-
neously recorded the compression force and time from
the tester. Grain deformation was then calculated and the
force}deformation curves plotted. Compression was
stopped when cracking of the grain was heard. The husk
was then manually removed to con"rm the yield. From
the force}deformation curves, k was determined and then
used to calculate s which was then substituted in Eqn (6)
to obtain the maximum deformation. Maximum impact
force was estimated using Eqn (2), the duration of impact
using Eqn (7) and "nal velocity of the grain after impact
using Eqn (1). Yield shear force was determined as the
maximum husking force between two rubber rolls using
the arrangement shown in Fig. 2. A computer simulta-
neously recorded shear force and time.