What Makes Popcorn Pop?

Some of the popcorn kernels need to soak in water for at least 8 hours or up to 24 hours before beginning this experiment. Make sure to use plain paper lunch bags without any writing on them (colored inks are often not microwave-safe).

1. Use masking tape and marker to label 1 airtight container “Hydrated” and second airtight container “Dehydrated.” (“Hydrate” means “to add water” and “dehydrate” means “to take away water.”)

2. Add ¼ cup popcorn kernels and water to container labeled “Hydrated.” Place lid on container and set aside for at least 8 hours or up to 24 hours.

3. Meanwhile, heat oven to 200 degrees. Add ¼ cup popcorn kernels to rimmed baking sheet and spread into even layer. Place baking sheet in oven. Bake kernels for 2 hours.

4. Use oven mitts to remove baking sheet from oven and place on cooling rack (ask an adult for help). Let popcorn kernels cool completely, about 15 minutes. 

5. Transfer popcorn kernels from rimmed baking sheet to airtight container labeled “Dehydrated.” Store at room temperature until hydrated popcorn kernels are ready. 

6. When hydrated popcorn kernels are ready, line 1 large microwave-safe plate with 2 paper towels. Set colander in sink. Pour hydrated kernels into colander. Shake colander to drain well. Transfer drained kernels to paper towel–lined plate. Use another paper towel to blot kernels until dry.

7. Use masking tape and marker to label 1 bowl “Hydrated,” second bowl “Dehydrated,” and remaining bowl “Control.” (In a science experiment, a control sample does not have any variables changed—in this case, the amount of water in the kernels is our variable.)

8. Make a prediction: What do you think will happen when you pop the hydrated kernels, the dehydrated kernels, and the control kernels? Will the popped popcorn look the same or different? Why?

9. Add remaining ¼ cup popcorn kernels to 1 paper lunch bag. Drizzle kernels with ½ teaspoon oil. Fold over top of bag 3 times to seal (do not tape or staple it). Shake bag to coat kernels evenly with oil, place bag on its side on large microwave-safe plate, and shake kernels into even layer in bag.

10. Place plate in microwave and cook until popping slows down to 1 or 2 pops at a time, 3 to 5 minutes. Use oven mitts to remove plate from microwave (ask an adult for help). Carefully open paper bag (be careful of hot steam) and pour popcorn into bowl labeled “Control.”

11. Repeat steps 9 and 10 with hydrated and dehydrated popcorn kernels, using different microwave-safe plate each time. 

12. Observe your results: Compare your 3 samples. Do they look similar or different? Which bowl is filled up the most? That’s the fluffiest popcorn! Taste each sample. Which is your favorite?

13. Eat your experiment: Add 1 tablespoon melted unsalted butter to bowl of control popcorn. Use rubber spatula to toss popcorn with butter. Sprinkle with ¼ teaspoon table salt. Serve.

In the ATK Kids Recipe Lab, we found that the control popcorn kernels produced the fluffiest popcorn, the dried kernels produced less fluffy popcorn, and the soaked kernels produced hard popcorn that was the opposite of fluffy. 

Every popcorn kernel is surrounded by a hard outer layer called the hull. Inside the kernel you’ll find the germ and the endosperm. The endosperm is made of starch, tiny droplets of water, and a bit of protein. As kernels heat up, those tiny droplets of water expand and turn into steam, pushing against the tough hull. When enough pressure builds up inside the kernel the starch BURSTS through the hull and quickly solidifies in the cooler air—kind of like a small, corny balloon. The white-yellow, billowy part of popcorn? That’s solidified starch. 

If you change the amount of water inside a popcorn kernel, by either soaking or drying it out, you’ll definitely change the way it pops!

Drying the kernels in the oven causes some of the water inside to evaporate, so less steam builds up inside the kernels as they cook. When a dehydrated kernel finally does pop, there isn't as much force to make it fluffy. Think about popping a half-blown-up balloon (your dehydrated popcorn) versus popping a fully blown-up balloon (your control popcorn). The fully blown-up balloon would pop with more force, since there’s more gas and pressure in the balloon. Same with popcorn. 

As the hydrated kernels soak, water travels through their hulls into their starchy interiors, making them expand and making the hull weaker. This causes the hydrated kernels to pop before much pressure builds up inside the kernel. They make some loud popping sounds in the microwave, but the results are pretty flat—literally!