Cooking With Science: Why Does Popcorn Pop?

What is Popcorn Made Of?

Popcorn is a whole grain.

• Popcorn is made from corn kernels. It is the only type of corn that can pop!
• A kernel of popcorn has three parts: 
  • Germ (the very middle)
  • Endosperm
  • Pericarp (the hull).
• There are several varieties of corn, including sweet, dent, flint (Indian corn), and popcorn.

Why Does Popcorn Pop?

Let’s discover how all three states of matter (solid, liquid, and gas) contribute to the making of popcorn.

• Each kernel of popcorn (solid) contains a small drop of water (liquid) stored inside a circle of soft starch.  The kernel’s hard outer surface surrounds the soft starch.
• Popcorn needs between 13.5-14% moisture to pop.
• As the kernel heats up, the water expands and turns into steam (gas). Pressure builds up inside the kernel before finally bursting the hull open.
• As it explodes, steam inside the kernel is released. The soft starch inside the popcorn becomes inflated and spills out.

Shape of Popcorn

Popcorn pops into different shapes because of the unique way its kernel is designed.

The shape of the popped popcorn depends on how the kernel’s outer hull breaks open when the steam bursts out. 

Factors such as the thickness of the hull, the distribution of moisture inside the kernel, and the temperature and pressure during popping can influence the shape. 

• Butterfly popcorn: Popcorn with several lobes.
• Mushroom popcorn: Popcorn that expands uniformly.

 

Fun Facts

 

Here are some interesting facts about popcorn:

• Popcorn is over 5000 years old. 
• The first commercial popcorn machine was invented by Charles Cretors in 1885.
• Popcorn is a healthy, GMO-free, and gluten-free snack.
• Popcorn can reach up to 3 feet in distance when popping.
• The unpopped popcorn kernels at the bottom of a popcorn bag are called “old maids.”

 

Review

 

Let’s quickly recap what we learned about the science behind popcorn:

• What are the three parts of popcorn? Germ, Endosperm, and Pericarp
• What is stored inside a circle of soft starch in the kernel? A Drop of Water
• How much moisture does popcorn need to pop?  13.5 to 14 %
• What happens to the water when the kernel heats up? Turns into Steam
• What spills out when the kernel bursts open? Soft Starch 
• What are the two common shapes of popcorn? Mushroom & Butterfly