Why Does Popcorn Pop? | A2 ESL Science Reading Passage

A hard seed becomes a light snack in seconds. Read about what happens inside, then try five questions.

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An illustration of popcorn beside unpopped kernels.

Reading Level: A2–B1

Word Count: 180 words

Reading Passage

A bowl of popcorn looks very different from the small seeds used to make it. Heat causes this change, but something inside each seed makes it possible.

Each popcorn kernel contains a little water and starch. A hard outer layer, called the hull, surrounds them. The kernel may feel dry, but there is still water inside.

When the kernel gets hot, some of its water becomes water vapor. The gas pushes against the hull. Because the hull holds it inside, pressure builds up. The starch also becomes soft as the kernel heats up.

Eventually, the hull cannot hold the pressure any longer. It breaks open, and the water vapor escapes. The soft starch quickly spreads out and grows bigger. As it cools, it becomes the light, crisp part of popcorn.

Not every kernel pops well. A kernel needs the right amount of water inside. If it has too little or too much, it may not pop properly. Popcorn is also a special kind of corn. The sweet corn people eat with dinner does not turn into the same fluffy snack.

A simplified illustration of the changes inside a popcorn kernel.

Key Vocabulary

Word	Meaning
kernel	a single seed of corn
starch	a substance in plants that stores food
water vapor	water in the form of a gas
pressure	the force of something pushing on a surface

Reading Questions

1. What two things are inside a popcorn kernel?
2. What happens to some of the water when the kernel gets hot?
3. Why does pressure build up inside the kernel?
4. What becomes the light, crisp part of popcorn?
5. Why might a kernel with too little water not pop properly?

Answers

1. Water and starch are inside it.
2. It becomes water vapor.
3. The hull holds the water vapor inside as it pushes against the hull.
4. The starch spreads out, grows bigger, and becomes crisp as it cools.
5. A kernel needs the right amount of water inside to pop well.

A close-up illustration of a hard kernel and crisp popcorn.

Short Summary

Heat makes water vapor build pressure inside a kernel. When the hull breaks, soft starch expands and cools into popcorn.

More Easy Readings

• How Does a Microwave Heat Food?

Science Sources

• American Chemical Society: The Secret Science of Popcorn
• Popcorn Board: What Makes Popcorn Pop?