Fig. 6 presents the pore size distribution of representative freeze-dried rice samples, as measured with mercury porosimeter, for various boiling periods. Fig. 6a and b presents the pore size distribution of rice kernels for 0.13 and 1.25 mbar of absolute freeze-drying pressure, respectively. The percentage of large pores increased with the increment of the boiling period for various applied pressures. As the boiling procedure is elongated, rice will absorb more water, resulting in expansion of the material and pro- duction of larger water-containing regions and larger ice crystals. Consequently, the sublimation of ice will create larger pores or gaps inside the kernel. In addition, Fig. 7 shows the pore size distri- bution of freeze-dried rice samples as a function of the applied pressure during freeze-drying. The percentage of large pores is higher at the lower applied pressure, where the porosity is higher. The higher applied pressure during freeze-drying leads to the reduction of viscosity of food materials which causes acceleration of shrinkage (Krokida et al., 1998). As a result, the porosity and pore size of rice kernels will be lower at higher pressures. These re- sults strengthen the observation obtained from helium stereopyc- nometer data, which indicate the high porosity with the decrement of the applied pressure.