Popping mechanism of popped rice

Abstract

This thesis presents the popping mechanism and the influence of temperature on the pore structure of popped rice. We compared the popping process of popped rice with popped corn. When a rice grain/corn kernel was heated by hot air, they exploded into popped products with an emitted characteristic “pop” sound. The thermally stable rice husk with an air-tight interlocking of lemma and palea made rice grain popped at a higher temperature as compared to that of popped corn. The higher popping temperature generated superheated water of higher pressure and greater mass of water involved in the popping process. The high pressure of superheated steam ruptured the rice husk. At this moment, the superheated steam exploded the microscopic starch granules into inter-connected starch balloons with micrometer-thin starch walls. SEM images confirmed larger pore sizes at greater popping temperature. The popped rice expanded about 21 times the grain volume while the popped corn expanded about 13 times the volume of kernel. During the popping process, the transformation of rice and corn did not undergo chemical changes as they only transformed their structures. Due to the higher popping temperature and the greater mass of water involved in the popping process, the popped rice jumped higher into the air with an instantaneous separation of popped rice and its husk.