Life is studded with little pockets of magic. These are the moments with mysterious emergent qualities, when the whole is greater than the sum of the parts, when one plus one somehow equals three. Such magic is even better when it comes in edible form.

When an unassuming little kernel of corn meets hot oil, it is transformed. It is elevated into with an unmistakable “pop!” into a fluffy cloud of goodness ready to be dressed with butter, caramel or whatever your heart desires.

This magic is called popcorn.

Popcorn has one of the longest and richest histories in all of American food lore. Some sources even purport that it was shared between Native Americans and settlers at the “First Thanksgiving” celebrated in 1630 (Smith, 3). While the hard evidence required to support or deny that claim has yet to be found, by 1848, popcorn was prevalent enough in the U.S. to be included in the Dictionary of Americanisms (22).

Popcorn exploded in popularity in the early 20^th century but surprisingly only made it into movie theatres with the advent of sound films, or “talkies,” in 1927. Silent films catered to a smaller, more exclusive clientele and owners worried that the sound of the snack being munched would detract from the experience (Geiling).

By the 1940s, popcorn’s popularity had made it an inextricable part of going to the movies, and from then on, over half of the popcorn consumed yearly in America was eaten at movie theaters (Geiling). Fast-forward some 70 years and the relationship remains unbreakable. Step into any movie theatre lobby across America and your senses are bombarded by the unmistakable scent of salt and butter.

Popcorn snuck into the American household in the 1960s with Jiffy Pop, a self-contained stovetop popper including kernels, oil, and even the pan, and flourished with the popularity of microwave ovens in the 1970s (Smith, 124). Popcorn cultivated an important relationship with microwaves in the latter half of the 20^th century, important enough to have bequeathed upon it the rare honor of its own designated button (127).

“But how?” you might ask. How has popcorn continued to be among the most popular American snacks year in and year out? How do these ordinary kernels magically spring to life with a little heat and oil, enchanting kids and grown-ups alike?

Like most acts of magic, popcorn’s “pop” can be understood with a little science.

Botanically speaking, popcorn is a type of maize, the only domesticated subgroup in the genus Zea, a group of plants in the grass family. The different types of maize are classified based on their kernel’s size, shape and composition (Smith, 6).

Corn kernels have three main structural components. First, there is the germ (from the Latin germen, meaning seed or sprout), a small pocket of genetic material essentially composing a baby corn plant waiting to grow. The germ is surrounded by the endosperm (the Greek endon, within, and sperma, seed), a larger parcel of water mixed with soft and hard starch granules that make up most of the kernel’s weight and would provide food for the corn plant if it were to sprout. Finally, the germ-endosperm complex is surrounded by the pericarp (from the Greek peri, around, and karpos, fruit), the hard shell that winds up stuck between your molars after enjoying a bag of popcorn (Ghose).

Popcorn kernels are unique in that they are relatively small, they have endosperms containing a larger number of hard starch granules, and their pericarps are hard and impermeable, essentially sealing off the contents of the kernel from the outside environment. These characteristics have endowed popcorn kernels with the ability to pop (Ghose).

When heat is applied to the kernels via hot oil on a stovetop or in a microwave, the temperature of the kernels begins to rise accordingly. Most affected by this increase in heat is the water stored between the starch granules in endosperm. Much like a bubbling pot of water brought to a boil, the water in the kernel begins to change from liquid into gas (Ponomarenko and Virot).

While liquid water is content to stay put, gaseous water in the form of steam craves space to move, but the hard shell of the pericarp effectively keeps it trapped inside the kernel. As a result, the kernel acts like a tiny steamer and the starch granules inside are cooked into a gooey mass. As the mass gets hotter and hotter, the steam presses harder and harder on the inside surface of the kernel’s shell like the hands of a million tiny creatures trapped inside a bubble (Ponomarenko and Virot).

The tension is palpable. The kernel begins to shake with anticipation. It rocks back and forth, back and forth, faster and faster, and faster still. Then finally … pop! The bubble bursts, the lid flies off the pot, fireworks explode, and a gospel choir sings “Hallelujah!” as the hard shell of the pericarp cracks and the steam breaks free from its kernel prison. The starchy goop also bubbles out into the world, where it meets cold, fresh air and rapidly hardens into spongy cloudlike shapes. Just like that, in just one-fifteenth of a second, a new piece of popcorn is born (Ponomarenko and Virot).

For those who enjoy numbers, a pair of French researchers (physicist Alexandre Ponomarenko and aeronautical engineer Emmanuel Virot), who seem to have also fallen under popcorn’s spell (judging by the language of their published report), conducted a study on popcorn and determined that the temperature at which kernels typically pop is 180 degrees Celsius. The pair also determined that the resulting popped kernel can be up to 40 times its un-popped volume, although usually the kernel’s radius merely doubles.

But what propels the kernel, with what Ponomarenko and Virot call “all the grace of a seasoned gymnast,” into the air as it pops? When the pericarp fractures, it does so in only one place first, giving some of the steam and starchy goop a head start on escaping. The starch released first extends to create a leg of sorts, off of which the rest of the kernel springboards, launching it somersaulting into the air like an Olympic gymnast. Popcorn jumps typically only reach a height of a few centimeters, but still manage to create endless entertainment for the hungry viewer (Ponomarenko and Virot).

But where does the “pop” sound come from? Arguably the most important part of the whole experience, popcorn’s characteristic noise is not, contrary to popular belief, the sound of the kernel’s shell breaking open. The popping sound is created by the release of trapped water vapor resonating in the kernel, similar to how, when removed, a champagne cork makes a popping sound that resonates in the glass bottle (Ponomarenko and Virot).

Making popcorn hardly seems like an opportunity to learn about physics, but the kernels’ unique transformation illustrates some principles of thermodynamics, biomechanics and acoustics, as the properties of different materials dictate how they respond to pressure and heat.

Life is studded with little pockets of magic. From the enticing smell during a night at the movies to the rising staccato sound of a bag coming to life in your microwave, popcorn is magic meets science in its most delicious form. And it always leaves you hungry for more.

 

Works Cited

Geiling, Natasha. “Why Do We Eat Popcorn at the Movies?” Smithsonian.com. The Smithsonian Institute, 3 Oct. 2013. Web. 20 Sep. 2015.

Ghose, Tia. “The Secret Acrobatics of Popcorn Revealed.” LiveScience, 10 Feb. 2015. Web. 19 Sep. 2015.

Ponomarenko, Alexandre and Emmanuel Virot. “Popcorn: critical temperature, jump and sound.” Journal of the Royal Society Interface 12.104 (Mar 2015). Web. 19 Sep. 2015.

Smith, Andrew F. Popped Culture : A Social History of Popcorn in America. Columbia, SC: University of South Carolina Press, 1999. Print.