Fissure formation in rice during conventional and microwave drying

. Rice fissuring and breakage have negative economic impacts on rice processing. Many advances in multipass conventional rice drying technologies have not been successful in completely preventing rice fissure formation. Thankfully, novel drying technologies such as the 915 MHz industrial microwave have been shown to have a great potential for rice drying and may reduce rice fissuring (or increase head rice yield) due to the volumetric heating property of microwaves. This review assessed the mechanism of fissure formation in conventionally and microwave-dried grains to provide recommendations for managing fissure formation during the drying of freshly harvested paddy rice. Literature search indicates that fissure formation during microwave drying may be mainly a combination of different phenomena, such as the buildup of high internal temperature and pressure in the kernel, stresses generated from a higher flux of liquid at high microwave intensities, and other mechanisms that are yet to be discovered. Fissure formation in rice during conventional drying of the rice kernels can be explained using the glass transition phenomenon.