Abstract:
Drying and milling of the
paddy are known as the most important
process influencing the rice grain breakage.
Therefore in this study, influence of
tempering period and the reduced
atmospheric pressure (vacuum) on the crack
formation of two rice varieties (Nemat and
Pajouhesh) during the tempering stage is
presented. Four different level of drying
temperature (40, 50, 60 and 70°C) were
used in this study. After drying, paddies
have been transferred to a vacuum chamber
ranging from 0.4 at to 1 atm (ambient
pressure). Based on the results obtained in
this study, crack formation in rice grains
increases with increasing drying time and
drying temperature. In contrast, a reduced
pressure during the relaxation stage
significantly reduced the rice grain
breakage. During the relaxation period in
the vacuum chamber, heat transfer within
the rice grain occurs slowly, yields
minimizing the thermal and moisture
stresses. The optimized combination of
temperature, time, and pressure for the
Nemat and Pajouhesh rice varieties obtained
60°C, 5 hr, and 0.8 atm, respectively.
