Hydration kinetics and energy analysis of parboiling Indica paddy.

Hydration of Indica paddy (variety IR-20) in hot water was studied as a function of time, pressure and
vacuum followed by pressure at temperatures ranging from 25 to 758C and time of soaking not exceeding 6 h.
Becker’s diffusion equation was used to predict the soaking behaviour of paddy. Soaking at 196 kPa and
above, maintaining temperatures of 658C, shows complete hydration within 2�5 h. Within the experimental
range studied, conditions such as hot water soaking under atmospheric pressure, soaking under vacuum alone
for 6 h and temperatures of 608C and below, will not result in the reduction of the soaking period as well as not
being sufficient for complete hydration necessary for parboiling. The activation energies of the diffusivity
through the grain were calculated using Arrhenius-type equation for diffusion dependence on temperature.
For the soaking conditions selected, the values of activation energy and diffusion coefficients of paddy were
found to be in the range of 19�49–23�09 kJ mol �1 and 0�406–0�647m2 s�1, respectively. The heat energy
required for the existing and proposed method of soaking amounts to 1�105 and 1�005 GJ, respectively. The
study showed that soaking of paddy involving heating of water to 758C, soaking at 658C, maintaining a gauge
pressure of 196 kPa and above, a reduction of soaking time from 4 to 2�5 h is possible over the existing process,
with a single-stage compression. Assuming perfect inter-cooling and neglecting inter-cooler pressure drops, the
power input can be further reduced by 5% with two-stage compression. The economic aspects of the suggested
method of parboiling as compared with the traditional method adopted indicated a saving of 4�4% besides
realising higher head rice yield and lower broken grains.