If you thought the secret to making delicious kettle corn at home was the temperature of the oil or the technique for adding the seasonings, you are partially correct. These do matter, but the real secret to producing puffy popcorn with a crispy, sugary coating is starting with the right kind of popcorn kernels.
Traditional movie theater popcorn is made from snowflake popcorn. These kernels pop big and fluffy with an irregular shape. Snowflake popcorn can be either white or yellow and is the most common type sold in stores for homemade popcorn. Commercial vendors of kettle corn use a different kind of popcorn kernels to produce ball-shaped popped corn that works well for holding a coating. This type of popcorn is called mushroom popcorn. It pops up tender and puffy and resists breaking and crumbling when handled. For the best homemade kettle corn, buy mushroom popcorn kernels. Gourmet popcorn suppliers sell mushroom popcorn kernels.
When the moisture inside a popcorn kernel is heated, it turns to steam and bursts the outer hull, creating popped corn. While they will pop at approximately 250 degrees Fahrenheit, for the fluffiest kernels and tastiest popped corn, they need to reach a temperature of 400 F or more. That means that popping corn requires medium to high heat. Lower heat may prevent burning but will also produce smaller nuggets of popped corn and more unpopped kernels. The trick to preventing burning your popcorn at high temperatures is to shake the kettle while you pop the corn to keep the kernels moving.
The sugary coating on kettle corn comes from adding the sugar with the oil before popping the corn. As the kernels burst open, the sugar mixes with the steam and coats the popped corn. How much sugar you use depends on how sweet you want your kettle corn. As a rule, start with approximately the same amount of sugar as oil and twice that amount for the corn kernels. For example, if you are popping 1/2 cup of corn kernels, you will need 1/4 cup of oil and 1/4 cup of sugar to make kettle corn. Add a teaspoon of salt per 1/4 cup of oil if you want sweet and salty kettle corn.
Add the oil, sugar and salt to the kettle and heat over medium-high heat. Drop in two to three popcorn kernels and listen for them to pop. This lets you know that the oil is at the right temperature for popping. Pour in the remaining kernels and cook, shaking constantly, until the popping slows. Do not wait until all kernels have popped because the sugar burns easily. Serve the kettle corn warm right from the pan or layer it on waxed paper to cool. Kettle corn will keep fresh for several days if stored in an airtight container.