From "Investigation of the properties influencing popcorn popping quality," Maga J.; Blach, B.; Developments in Food Science (1992), 29, 543-50:
The roles of popcorn moisture content and storage temperature prior to popping as well as popping temperature and the amount of added oil and salt on resulting popped volume and number of unpopped kernels were evaluated. Max. popped volume was in the 12.5-13.5% moisture range while the proportion of unpopped kernels increased with increasing moisture. Popped volume decreased while unpopped kernels increased with an increase in storage temperature. The addition of 2-4% oil maximized popped volume and minimized unpopped kernels. The addition of 2% salt gave the highest popped volume and the lowest amount of unpopped kernels. Optimum popping temperature was 180°.