It is known that the water binding capacity of starch increases after vacuum microwave treatment. Microwave radiation absorbed by the starch sample affects its sensible, latent internal and chemical (bond and conformational) energy levels. A phenomenological model was developed based on energy sinks in starch, practically described as increasing temperature, breaking bonds between water and amylopectin/amylose molecules, changing the phase of water from liquid to vapor and structural rearrangements at short (single/double helices) and long (crystalline/amorphous) order. The model was validated by experimental data for different vacuum microwave treatment parameters, viz, incident power (460, 500 and 750 W), duration (30 to 340 s) and sample mass (10 to 70 g) at 4000 Pa. The results provide an insight into the physical aspects of the process and would facilitate its development on an industrial scale.