The Chemistry of Popcorn

About a month ago my roommate, Tyler, and I were going to sit down and watch a movie. Since she was getting the movie ready, it was my task to get snacks from the store. What do you have to have during movies? Popcorn!

Except that we don't have a microwave...I had lived my entire life either on movie popcorn, made with fancy machines, or the microwavable bags. So in the store when I saw a bag of unpoped popcorn, I thought "I'm great in the kitchen, how hard could making popcorn be?"

At home I put some oil and kernels into my wok, placed a lit on it...

And out came real popcorn! Since then we have both been making more popcorn than I have ever seen in my life. And not just normal popcorn; barbecue, garlic, even creole! But how exactly does it work? What is the chemistry behind popcorn?

To start, we need to look into the basic anatomy of a popcorn kernel:

Picture courtesy by

Picture courtesy by

  • Pericarp: the hard outer shell of the kernel
  • Endosperm: made up of starch and water
  • Germ: actual seed

When the kernel is planted, the endosperm gives the germ a great head start in nutrients while developing first roots. The pericarp is hard enough to prevent invaders but soft enough for the germ to bust open when rooting.

The key to popping is the unique ratio of water to starch in the endosperm. If the water is about 14% of the endosperm, and the kernel is heated up to around 180* F, the water starts to become steam. That water vapor then tries to expand, but is met by the pericarp. The outer shell holds back the pressure as much as it can, but eventually succumbs to the pressure and pops! The starch then expands rapidly, solidifying as it meets the oxygen in the air. The steam escapes as well, leaving perfectly cooked popcorn!

But every time I have made popcorn there are some kernels that didn't pop. There are three possible reasons for that:

  • There is less than 14% of water in the endosperm, so even if heated up perfectly there would not be enough pressure built up to pop it
  • It could have not been heated up fast enough which would result in a 'no pop'
  • If heated up too fast the pressure builds up faster than the endosperm has time to 'cook' so when the pericarp breaks the endosperm still is somewhat hard

If you have never made popcorn on the stove before (not counting Jiffy-pop), I highly recommend you try. Knowing how heating kernels make such a wonderful treat makes them taste even better!


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