Salty Science: The Remarkable Research Behind Your Favorite Snack Foods

You’ve just nestled into the sofa to binge watch the latest Netflix series. What must-have snack are bringing to your couch potato marathon? Whether it’s sweet or salty, chewy or crunchy, you’re not alone in your love of these tasty treats. The average American spends about $500.00 per year on snack foods. With profits like these on the line, it’s not surprising that food science is a booming field. Here are just a few examples of the remarkable research behind your favorite snack foods.

Kernel of Truth

If you are a fan of microwave popcorn (and who isn’t), you know that listening for the intervals between pops is crucial to achieving perfectly fluffy popcorn. If you stop the microwave too soon, you’re left with lots of stubborn unpopped kernels. If you wait too long, the popcorn burns.

As you stand there waiting, have you ever wondered what makes popcorn jump or why it makes a popping noise? Well, so did a team of engineers in France, and they set out to find the answers using thermodynamics and fracture mechanics.

Each popcorn kernel contains a pocket of water surrounded by soft starch and a hard outer hull. When heated, the water inside the kernel turns to steam and expands, creating pressure against the hull. The heat also turns the starch into a gelatinous goo. Eventually, the hull cracks and explodes, releasing the steam. At the same time, the starch inflates and bursts out, becoming spongy as it cools.

The white “flakes,” as they are called in the popcorn biz, are two times larger and eight times less dense than the kernels that produced them.

Using a high-speed camera at 2900 frames per second, the French engineers were able to capture photos of individual kernels cooking on hotplates. They discovered that a starch “leg” emerges from the hull just after it fractures and triggers the jumping motion.

This leg, which is initially compressed against the hotplate, acts like a spring and pushes the popcorn into the air. A portion of the elastic energy stored in the starch leg converts to rotational energy, causing the popcorn to somersault like a gymnast.

To understand the origin of the popping sound, the researchers added a microphone to the camera setup. They found that the sound is triggered by the release of water vapor as the hull of the kernel begins to burst.

The signature pop occurs right before the jump and lasts for about 50 milliseconds. Although the pop of each individual kernel is brief, the successive popping of 400 to 500 kernels in a bag of microwave popcorn sounds a lot like the Fourth of July.

Hot Potato

It seems everyone has an opinion when it comes to potato chips. Do you prefer traditional or crinkle-cut? Are you a fan of sour cream and onion, or is barbecue flavor more to your liking? Regardless of your potato chip preferences, there is one thing everyone can agree on – the crispier, the better. No one likes a soggy chip.

Raw potatoes are about 80% water, and their internal structure is a matrix of starch granules and tiny interconnected pores. These microstructural features affect the oil uptake during frying, which ultimately impacts the texture of the potato chips. Too little or too much oil results in the dreaded soggy chip.

In 2016, a team of scientists at the University of Illinois used 3-dimentional (3D) imaging to study changes to the potatoes’ microstructural features during the frying process. They were particularly interested in how the number and size of the pores (porosity) and the twistiness (tortuosity) of the passages between the pores contributed to the uptake and dispersion of oil. 

The scientists fried uniform discs of Russet potatoes for 20, 40, 60, and 80 seconds and then created 3D models of the internal structures. They found that both the pore size and the oil flow changed as the length of the frying time increased.

With longer frying times, more water evaporated from the potatoes, and the pressure of the escaping water vapor created larger pores. These pores initially formed near surface, but as frying time continued, pore formation spread toward the core of the potato slice.

The passages between pores also changed when frying time increased. As the pores expanded in size, the pathways between them became less complicated (decreased tortuosity), allowing oil to flow deeper into the potato slice. The deeper penetration of oil produced crispier and tastier chips.

Knotty Situation

If you’ve ever felt your stomach rumbling or your mouth watering when you passed the soft pretzel kiosk in the mall, you can appreciate the potent power of pretzel aroma. The smell of these twisty treats is so adored that, in 2018, pretzel purveyor Auntie Anne’s delighted many pretzel lovers when they announced a line of pretzel scented essential oils. Sadly, the announcement was a well-orchestrated April Fools’ Day prank, much to the chagrin of loyal customers. 

Why does the smell of soft pretzels make you so eager to follow your nose to the nearest pretzel stand and empty your wallet for a bite of these salty snacks? A 2019 study may have found the answer.

During the pretzel-making process, the raw dough is treated with lye, giving pretzels their shiny brown crust and imbuing them with their distinctive scent. The crust contains a number of volatile aromatic compounds, but only a small portion of them can interact with the olfactory receptors inside the human nose.

A pair of German scientists set out to identify the precise chemical compounds responsible for the distinguishing scent of these doughy delights. The scientists extracted the volatile compounds from the pretzel crust and separated them using gas chromatography. After conducting a sniff test to determine which of the extracted compounds elicited odors, they identified those compounds using mass spectrometry.

Next, a team of specially trained super sniffers helped isolate the compounds most responsible for the pretzel scent. Initially, the testers detected several different aromas, including malty, buttery, cheesy, honey-like, caramel-like, and even sweaty.

Using a series of elimination tests, they finally identified the roasty, popcorn-like smell (2-acetyl-1-pyrroline) and the caramel-like aroma (4-hydroxy-2,5-dimethyl-3(2H)-furanone) as the key odorants in the soft pretzel crust. Some of these same compounds are found in the crust of wheat bread, but the quantities and proportions differ from those in pretzels.

Now that scientists have identified the compounds that give pretzels their seductive scent, perhaps those essential oils aren’t too far-fetched after all.

To learn more about food science, check out this post about bananas.