Influence of Soaking on Crushing Strength of Raw and Parboiled Rice

Hardness (crushing strength) of rice decreased with increase in soaking time. A remarkable
reduction was observed after complete hydration in parboiled rice (~85%) than raw
rice (27%), which was attributed to greater hydration capacity of parboiled rice (63%
d.b.) compared to raw rice (38% d.b.). Crushing strength of unsoaked parboiled rice
(~150 N) was greater than raw rice (~76 N). On the contrary, crushing strength of fully
hydrated parboiled rice (~23 N) was lower than raw rice (~55 N). The significant
decrease in the hardness of parboiled rice grains upon hydration, however, could not
explain the greater energy requirement for wet grinding parboiled rice studied earlier,
which, perhaps, could be attributed to the higher slurry viscosity of parboiled rice compared
to raw rice.