By Markham Heid
March 28, 2018

If you’ve ever wondered exactly what happens when a popcorn kernel pops, well, scientific research has the answer. An un-popped corn kernel is a drop of water surrounding by soft starch and encased in a hull. Heat up that kernel, and the water molecules locked inside will expand until the pressure and heat cause the starch to inflate and explode, bursting the hull and turning the kernel inside-out.

What you have left after this popping occurs is a filling, low-calorie, whole-grain food packed with fiber. “Popcorn is an extremely nutritious snack compared to most,” says Joe Vinson, a professor of chemistry at the University of Scranton.

Along with fiber, popcorn is a source of polyphenols—a type of plant antioxidant linked to improved cell health. Most fruits and vegetables are mainly water—meaning you have to eat a relatively large portion of them to get meaningful amounts of their healthful nutrients, Vinson says. Popcorn is a much more condensed source of antioxidants. Vinson’s research has shown that a serving of popcorn contains roughly double the amount of polyphenols as a serving of fruit (although fruit may have different or more numerous amounts of other vitamins and healthy phytochemicals).

But while popcorn in its natural state is a snack you can feel good about, how you prepare it can lessen its healthful properties.

Research has linked the coatings used in microwave popcorn to health issues. “One of the ingredients found in many brands of microwaveable popcorn is diacetyl, a flavoring which has been linked to the lung disease bronchiolitis obliterans,” says Anna Taylor, a clinical dietician with Cleveland Clinic. That disorder is nicknamed “popcorn lung,” for the condition contracted by some workers in microwave popcorn factories — though the risks aren’t clear for people who only eat popcorn, and don’t work with it.

Reports from the Environmental Working Group and others have also revealed that some chemicals used to coat microwave popcorn bags and keep the oils inside from leaching through are likely carcinogens. Those reports led the FDA to ban some of these chemicals from popcorn bags and other consumer goods. But there’s no guarantee the chemicals replacing them are any safer, the EWG says.

While those health concerns associated with pre-bagged microwave popcorn are not definitive, other prep methods are probably safer choices, Taylor says.

But even if you heat popcorn kernels in a stovetop crank-style popper, experts say there are some reasons to be wary. Some people add oil to their naked corn kernels in order to encourage rapid heating. But many oils will burn and smoke before the popcorn has popped.

That’s bad. “Anytime you burn fats or oils, you run the risk of creating chemical compounds that potentially can cause oxidative damage to cells,” says Lona Sandon, an assistant professor in the department of clinical nutrition at the University of Texas Southwestern Medical Center. How bad this burned oil is for you depends on how often you consume it. “There is not definitive data on just how much you would have to eat for it to be a problem,” she says. But if you’re coating your popcorn in scorched oil every night, that’s not ideal. “In general, it is not advised to eat burned oil or fat regularly, no matter what type of food you are cooking,” she adds.

Some oils have a higher smoke point than others, and so may be safe to employ for stove-top popping. “Peanut, corn, soybean and sesame oil have high smoke points,” says Marie-Pierre St-Onge, an associate professor of nutritional medicine at Columbia University’s Institute of Human Nutrition. “If using these oils, higher heat can be tolerated.”

But the healthiest prep method of all is one that removes oil from the equation. “If you are an avid popcorn eater, it is probably best to go with air-popped,” Sandon says. Electric air poppers are inexpensive and energy efficient, and good ones heat up popcorn quickly and thoroughly enough to ensure you end up with fluffy, bulbous pieces.

If you’re wondering just how hot popcorn has to get for a perfect pop, two French researchers have you covered. Their 2015 study found that 356 degrees Fahrenheit is the ideal temperature at which to pop your kernels. Simply spread naked popcorn kernels on a baking sheet and slide it into an oven preheated to 356 degrees, says Emmanuel Virot, first author of the study, who is now a postdoctoral research fellow at Harvard University.

It’s not the easiest way to make popcorn, but it is the funniest, Virot says, because your popped kernels will end up all over your oven. You’ll have to pick up those scattered pieces, but you’ll enjoy the show through your oven window.

Contact us at editors@time.com.

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