Physicist presses corn cooking process to create super-size snack

Monday, July 31st 2000, 12:00 am
By: News On 6

By Emily Sohn / The Dallas Morning News

Big screens can magnify movie watching. Big popcorn could magnify movie munching.
Physicist Daniel Hong has found a way to at least triple the size of popcorn, and he has yet to identify a limit. With the route to popcorn grandeur now open, further research might help scientists better understand how a hard kernel of unpopped popcorn becomes a fluffy white nugget of snack food.

The physics of popcorn is actually quite simple, said Dr. Hong, of Lehigh University in Bethlehem, Pa. A popcorn kernel is not the completely solid pebble it appears to be – water lurks inside. As a popper or microwave warms up, water in the kernel gets hot, turns to gas, and expands. Like steam building inside a teapot might pop the kettle's top, pressure builds inside the kernel until its shell bursts. When the explosion happens, starch trapped inside the corn kernel expands. The result is the textured snowflake of fluff so popular in movie theaters and amusement parks around the world.

Knowledge about the popping process has already made possible many popcorn improvements. Most popcorn research to date has focused on corn genetics, said Bruce Hamaker, a food chemist at Purdue University in West Lafayette, Ind. Selective breeding has made popcorn kernels spherical, small and dense, a form that optimizes pressure buildup, Dr. Hamaker said.

But Dr. Hong may be the first to use physics to push the size limits of the light and airy snack food. He encountered the unusual challenge in a dinner speech at a physics meeting in March. A few days later, the idea came to him. By lowering the air pressure around the kernel, he figured he could make bigger popcorn.

Anyone who has ever driven up a mountain with a sealed bag of potato chips may have noticed the big popcorn effect. At higher altitudes, less air pressure pushes down on the bag. So air inside the bag expands, and the bag puffs up.

Instead of zooming up a winding road, Dr. Hong put popcorn kernels in a vacuum chamber, then pumped air out. Like a chip bag at high elevations, the popcorn expanded more when popped in a low-pressure environment.

Dr. Hong worked out an equation to predict the size of popcorn popped under different amounts of air pressure. Reducing pressure in the chamber to slightly less than half of normal air pressure, for example, would double the size of the popped product. Tripling popcorn size would require reducing the chamber's pressure to about one-quarter normal air pressure.

Preliminary experimental results so far this summer reveal a somewhat more complicated interaction between a popped kernel's radius and its overall volume. But in general, his results back up his model, Dr. Hong said. He has submitted his work to the journal Physical Review E.

Dr. Hong's technique seems like the most logical way to make popcorn bigger, Dr. Hamaker said. "If someone asked me how you could do that, that would probably be the way I would suggest trying." Not a huge popcorn fan himself, Dr. Hamaker said that the motivation to make a piece of popcorn as big as a grapefruit has been essentially nonexistent.

Dr. Hong agreed. Though he likes to eat popcorn, Dr. Hong acknowledged that he never craved more than what he already had. "Probably no one was interested in making big popcorn," Dr. Hong said. "If they had wanted to make big popcorn, they would have come up with this idea."

Still, like a famous mariner's first encounter with the New World, the technique opens new avenues for exploration in popcorn research. "It's like the Columbus question," Dr. Hong said. "Once someone does it, it's easy."

The future of big popcorn is still uncertain. For one thing, it's unclear how big popcorn can actually get. "I'm sure there should be a limit," he said, "but to find out a practical limit ... I'd have to take into account many things."

Oil, for example, acts as a second shell, so more pressure has to build inside buttered popcorn kernels before they pop. Salt can also hamper a kernel's ambitions, reported a group of Purdue scientists in 1993. And physical characteristics, such as shell thickness, kernel shape and moisture content, alter the size of the final product. Most varieties of corn won't pop, in fact, and popcorn kernels must contain between 13 percent and 14 percent moisture by weight to pop well.

With so many challenges already facing popcorn production, a quest for big popcorn may seem excessive. But the novelty factor of colossal popcorn is one draw to pursuing this kind of research. The vacuum chamber method might also be economically appealing to industries, Dr. Hong said. Getting more snack from each seed could save money.

Big popcorn is intriguing to Dave Lewis, owner of the Great American Popcorn Co. in Galena, Ill. He already uses two kinds of popcorn. For a highly textured snack, his company pops the "butterfly" variety, whose kernel takes on a teardrop shape. But he also uses "mushroom" popcorn, which emerges from a rounder shell in a more compact, buttonlike form and can better hold caramel or cheese without falling apart.

Mr. Lewis said he would consider selling big popcorn, but he's not sure how profitable it would be. "I'd love to say, 'Come look at our popcorn; it's 10 times bigger than normal,'" Mr. Lewis said. "I don't know if I'd sell much. You'd only have two kernels and you'd be done."

Beyond the precarious practicalities, Dr. Hong's work stands as an example for how physics can help people understand everyday things. "One thing I learned is that maybe I can use physics to solve many practical problems," Dr. Hong said. That might win science some unlikely fans, he said. "You know, people don't like science. Kids think it's very abstract and has nothing to do with real life. I think popcorn is probably one way to hook kids."