Peer review

During the popping of popcorn the pericarp acts as a pressure vessel. It was found that the initial break in the pericarp affects popped volume more radically than do any subsequent breaks. Popping occurs at about 177 °C, which is equivalent to a pressure of 135 psi inside the kernel. Most of the water in the kernel is superheated at the moment of popping and provides the driving force for expanding the kernel once the pericarp ruptures. At temperatures below 177 °C the proportion of kernels that have popped declines markedly. The scanning electron microscope was used to document changes occurring in the kernel as a result of popping. In the translucent endosperm the superheated water appears to vaporize into the hilum, expanding the starch to a thin film. In the opaque endosperm large voids are produced and the starch granules remain birefringent. The voids around the starch provide an alternative site into which the superheated water vaporizes. Thus, the starch granules are not expanded and retain their birefringence.

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