Limited multilayer desorption of brown, parboiled rice

Two mathematical models, the BET-equation and the Caurie-equation, are used to analyse experimental desorption isotherms of two long-grain varieties of brown, parboiled rice at different temperatures. Monolayer moisture contents and maximum number of sorbed water layers, estimated by the Caurie-model, decrease with increasing temperature. From the temperature dependence of the desorption isotherms, isosteric heats of desorption are calculated. For both varieties, the differential heats of desorption are already very small (1.4 kJ/mol) at a moisture content of 20%. Thus, additional moisture behaves almost like pure water.