About the Effect of Moisture on the Popping of Popcorn Kernels

Moisture content needs to be just right for a popcorn kernel to burst to its maximum fluffiness.

Freshly popped popcorn is a treat, but if there's too much moisture inside the kernels, the popcorn turns out tough and chewy. Too little moisture, and not enough pressure can build up inside the kernels for them to properly explode.

Why Popcorn Pops

What sets popcorn apart from other grains, and even from other corn varieties, is how very tough its hull is: It can withstand internal pressure of up to 135 pounds per square inch (PSI). The hull is also nonporous. When the moisture in the endosperm heats up into expansive steam, there's only one way for the steam to come out: by popping. The starch inside cooks into a soft paste, which explodes into an airy foam when the kernel bursts.

Storage After Harvest

When popcorn is harvested, there's too much moisture inside the kernels. They won't pop right, and they can mold. The harvested corn must be conditioned until kernels contain no more than 13.5 percent moisture.

Reviving Overdried Kernels

If your corn has been in the pantry for a long time, it might be overdried. Place the kernels in the refrigerator, in an open container, for several days. In this environment, the corn takes on more moisture, regaining a good deal of its original pop.

References

• Purdue University: Alternative Field Crops Manual; Popcorn
• "Bull Cook and Authentic Historical Recipes and Practices"; George Leonard Herter, Berthe E. Herter; 1969
• The Old House Web: Popcorn; Moisture
• Cretors: Pop Science; How Popcorn Pops