Popcorn kernels only pop perfectly when their internal moisture is between 13.5% and 14%.

The science of popcorn is centered on the unique structure of the Zea mays everta kernel. Unlike other corn varieties, popcorn has an unusually thick outer shell called the pericarp, which acts as a pressure vessel. Inside the kernel is a small droplet of water surrounded by a circle of soft starch. As the kernel heats up to approximately 355 degrees Fahrenheit (180 degrees Celsius), the internal water turns into pressurized steam.According to research from Purdue University, the ideal moisture content for a successful pop is exactly 13.5% to 14%. If the moisture is too low, the kernel lacks the steam volume necessary to rupture the hull, leaving behind unpopped kernels known as 'old maids.' If the moisture exceeds 14%, the internal pressure builds too rapidly, causing the hull to fail before the starch has fully gelatinized. This results in a dense, crunchy texture rather than a fluffy one.When the hull finally bursts at a critical pressure of about 135 pounds per square inch, the gelatinized starch expands rapidly into a foam. This foam cools almost instantly, solidifying into the white, crispy structure we eat. Maintaining this moisture balance is so critical that commercial processors use airtight silos and specialized packaging to prevent the kernels from drying out or absorbing humidity from the air. This ensures that the expansion ratio remains high, often reaching up to 40 to 50 times the original kernel size.