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 (similar to 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 (similar to 150 N) was greater than raw rice (similar to 76 N). On the contrary, crushing strength of fully hydrated parboiled rice (similar to 23 N) was lower than raw rice (similar to 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.