What’s in a Kernel?

• The popcorn kernel is the seed of a special kind of corn, known as popcorn. It consists of a tough outer shell, starch, and a trace amount of moisture. The moisture and heat are the keys to the kernels in your bag of microwave popcorn bursting open and releasing the starch inside the kernel, forming what we refer to as popcorn. To do this, conditions need to be just right.

Moisture Content

• To pop properly, popcorn needs between 13 and 14 percent moisture in the kernel. This means that farmers dry the kernels to the right amount of moisture and seal them in airtight containers to prevent the moisture from evaporating or to prevent the kernel from absorbing more moisture from the air. The popcorn kernels in a bag of microwave popcorn have been sealed with a plastic wrap around the bag to maintain the right amount of moisture for popping in the microwave.

Temperature

• When the kernel is heated, the moisture inside the kernel turns to steam. This occurs at about 212 degrees Fahrenheit, but that is not hot enough to pop the kernel. As the steam reaches higher temperatures, it continues to expand and exerts increased pressure against the outer coat of the kernel. At approximately 347 F, the pressure inside the kernel becomes strong enough to split the outer coat of the kernel. The steam bursts forth and the starch, which has turned to a gooey mass, spills out and dries instantly as it hits the air. This forms the white fluffy kernel of popcorn. The microwave heats each kernel quickly, which causes the kernel to pop.

Oven Conditions

• A bag of microwave popcorn will not pop in a standard oven for several reasons. Because the oven is filled with hot air and does not deliver heat directly to the kernel, as the microwave does, it takes longer for the center of the kernel to reach the desired temperature. When the kernels heat slowly, the moisture seeps out of the kernel and the moisture content drops below 13 percent. This means that the kernel no longer has enough moisture to explode the shell and create a fluffy kernel of popcorn. A microwave popcorn bag may catch fire in the oven or the kernels may burn because they are not moving. Some kernels may sputter and crack open, exposing a small amount of starch, but putting a bag of microwave popcorn in the oven will not result in a bag of fluffy corn.