National Popcorn Day (January 19, 2023)

Jan 18, 2023 • 3:08 PM UTC

Rock Hill, SC, USA

140x Magnification

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Holly Stuart

Education Specialist at Foldscope Instruments

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Thursday, January 19th is National Popcorn Day, so I decided to get a head start and take a closer look at this delicious snack by putting it under the Foldscope! Enjoy!

Figure 1. Unpopped popcorn kernels in a petri dish on a light box.
(Photo Credit: Holly A. Stuart)

Popcorn kernels are small, hard, and protected by a waterproof transparent outer layer called a pericarp. This outer layer is key to the popping of popcorn. Because it is a solid waterproof seal, nothing can get in or out without a great deal of pressure being applied to it.

Figure 2. A view of the pericarp under a Foldscope at 140X magnification plus 5X zoom on my phone.
(Photo Credit: Holly A. Stuart)

Inside the kernel is a mixture of starch and water molecules. The image below shows a cross section of an unpopped kernel of corn. The small dark colored spots are the pockets where the water droplets are situated. The rest of the yellow material is the starch, which is the food source for the seed of corn.

Figure 3. A view of the cross section of an unpopped corn kernel under a Foldscope at 140X magnification plus 5X zoom on my phone.
(Photo Credit: Holly A. Stuart)

When the unpopped corn kernel gets heated up to a high enough temperature, the water turns to steam and expands. The expansion of the water molecules causes a tremendous build up of pressure. When the pressure inside becomes too much for the pericarp to contain, a mini explosion occurs. This rapid release of the excess internal pressure allows for the expansion of starch molecules and results in a popped kernel of corn. The image below shows a cross section of a popped corn kernel. The compact starch molecules have expanded and the spaces where the water molecules once were are now filled with air and and the whole thing now looks light and airy - like bubbles!

Figure 4. A view of the cross section of a popped corn kernel under a Foldscope at 140X magnification plus 5X zoom on my phone.
(Photo Credit: Holly A. Stuart)

So, the next time you pop popcorn, you can thank the laws of physics that explain why pressure builds up inside a kernel causing it to pop! And of course, you should always take time to check out your popcorn under a Foldscope! Happy National Popcorn Day!