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The Maize Page

Could you or one of your students guide me to information about how or why popcorn pops?

Hello Erika,

"Popcorn" is an ancient type of corn that contains a hard, glassy (or "vitreous") type of starch on the outside, and a softer, "floury" starch on the inside. In fact, it is probable that popcorn was the original type of corn, and that the first human use of corn grain as a food item ocurred when people realized that when they parched this grain, a formerly hard kernel became soft and edible.

Most of the inside of a kernel is composed of starch, which is a storage carbohydrate, or fuel. This starch is known as the seed's "endosperm" (meaning it is inside the seed). Its purpose is to provide energy for the living part of the kernel, the "germ" or embryo, once this embryo germinates and establishes a new plant. Starch has a large water holding capacity, and for this reason it has a number of industrial uses as a dehydrating agent in powder form. When you heat popcorn, the water that is ordinarily bound in the floury endosperm becomes a vapor and bursts through the fruit case, or "pericarp" of the kernel. In order for this to happen successfully and dependably, therefore, the kernel must be relatively small, and the hard, or flinty, outer shell of the kernel must be quite strong to resist the building pressure. This is why popcorn produces grains that are smaller than most field corn.

For an enjoyable experiment that will teach you about the process of corn popping see this page from the Ohio Corn Marketing Program's Kid Corner.

Greetings from Iowa, and best of luck with your report.

Ricardo J. Salvador

I have a batch of popcorn that is not popping. Applying what I have read on your page I assume that the problem may be that my popcorn has dried out. I have had it stored in an open and exposed container. My guess is that if I moisten the kernels they should recover their ability to pop. Is this possible?

Most likely, you are right and the problem is that the popcorn has dried out. An old rule of thumb is that adding one tablespoon of water to a quart of unpopped popcorn kernels will raise the moisture content 1%. The optimum moisture is 14%.

Put unpopped kernels in a glass quart jar, add 1 tablespoon of water, make sure jar is sealed so that no moisture can escape, shake well; 1 hour later shake well again. Over the next 4 to 7 days shake vigorously 2 to 3 times a day, then try popping the popcorn.

If the corn still doesn't pop well, repeat the above procedure. If the original popcorn was not in a moisture proof container it may have dried down to around 9% to 10% moisture, so it may take awhile to get it rehydrated. With situations like this, usually this is the best place to start. Let me know how it works for you.

Ken Ziegler
Popcorn Specialist
Iowa State University Agronomy Department

P. S. The procedure worked, and needless to say the writer was very pleased with the results!

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