“It’s bothersome,” says Bruce Hamaker. He’s a food chemist at Purdue University in West Lafayette, Indiana. “It can chip teeth if people aren’t paying attention.”

Artville

Instead of just grumbling about the problem, Hamaker and his coworkers have used science to try to figure out a way to reduce the number of unpopped kernels at the bottom of a bag of microwave popcorn.

The results may do more than just do away with the annoyance of biting into rock-hard kernels in the middle of a movie. Popcorn is an important crop in Indiana, Nebraska, and other states. Growing types of popcorn that pop better than current varieties do could improve popcorn sales.

Pressure cooker

Not just any type of corn will pop. Popcorn kernels are rounded and hard on the outside. They contain moisture on the inside. For a kernel to pop properly, water must make up between 14.5 and 15 percent of a kernel’s weight

Each kernel of popcorn is like a pressure cooker waiting to blow. As a kernel heats up in a microwave, pot, or air popper, water naturally found inside heats up, turns to gas, and expands. The pressure builds up inside the heated kernel until its shell bursts.

These little explosions turn kernels inside out, leaving behind airy balls of fluff that somehow make movies more special.

Depending on the variety of popcorn, kernels pop to form one of two shapes. The “butterfly” type, which is most common, is big and fluffy and looks as if it has wings. The “mushroom” type is round and compact. It’s better at holding cheese, caramel, and other coatings without falling apart.

The “butterfly” type of popcorn is big and fluffy.

Fatty coatings

To tackle the unpoppable popcorn problem, Hamaker and his coworkers started with a hunch.

Previous research had suggested that certain kernels lose moisture too quickly, either when stored or when heated. Without the proper amount of steam inside, the kernels would then fail to pop.

So, the researchers began by looking for coatings that would prevent moisture loss. Pretty soon, they found that coating kernels with certain types of fat could practically eliminate unpopped kernels.

Coating kernels before popping them isn’t an ideal solution, however. Extra fat could make popcorn greasy. And adding coatings would create more work for popcorn processing companies.

“They’d rather not add something to the process,” Hamaker says.

Crystal hull

Instead, the scientists decided that it might help to understand why some kernels lose moisture faster than others do in the first place.

Food chemist Bruce Hamaker has studied a variety of foods. Here, he’s examining samples of sorghum.

Purdue University

So, they studied 14 varieties of popcorn that had different microwave popping qualities. When the worst varieties were heated, as many as 47 percent of the kernels didn’t pop. The best varieties had only a 4 percent failure rate.

The secret, it turns out, lies in the structure of a kernel’s outer hull, also called the pericarp.

One-third of a popcorn kernel’s hull is made up of a material called cellulose. Found in all plant cells, cellulose is a kind of carbohydrate—a compound made up of carbon, hydrogen, and oxygen.

When heated, the cellulose in a kernel’s pericarp rearranges itself into an orderly structure known as a crystal. “It’s interesting that cellulose would undergo this kind of transition,” Hamaker says.

The crystalline sheet is tighter than the original cellulose, which is only partially ordered. “It forms a better barrier,” he says, “and keeps moisture in the kernel better.”

Why some popcorn kernels are better poppers than others depends on how orderly these crystalline sheets are, the researchers found. The best poppers have cellulose that’s especially good at turning into crystals.

Better coatings

This popcorn research could prove useful to popcorn growers. One good strategy would be to breed corn that produces kernels with pericarps made of a type of cellulose that turns into nice crystals.

NASA

The chemical processes involved in popcorn popping could also end up being of interest in other fields of food science, Hamaker says. Perhaps scientists could come up with cellulose coatings that would keep moisture inside fruits or grains and keep them fresher longer.

Hamaker had never studied popcorn before. After endless batches of popcorn, popped and eaten in his lab, he was surprised at how much there is to learn about something as seemingly simple as popcorn.

“Everything’s more complicated than you think,” Hamaker says. “The interesting thing about science to me is when you learn something unexpected that gives you an answer to a problem you’re working on.”

Going Deeper:

Additional Information

Questions about the Article

Word Find: Popcorn

Science Project Brainstorms

Are you interested in investigating popcorn? Here are some questions that may be worth tackling.

• How does the type of coating (fat) affect the number of unpopped popcorn kernels?
• Do different brands of popcorn leave different amounts of unpopped kernels?

For other science project ideas, go to www.popweaver.com/popcorn101/science/
science_list.html (Weaver Popcorn Company) or www.exploringminds.ca/e/featuring_science_fair/
qp_pop_corn.html (Exploring Minds).

You might want to dwell a little longer on the conditioned air that magically wafts out of household vents, however. The way you heat or cool your home has a big effect on the Earth, says John Carmody. He’s director of the Center for Sustainable Building Research at the University of Minnesota in Minneapolis.

“Most people don’t usually think about where their heat comes from,” Carmody says. Yet nearly every type of energy source dumps waste or spews pollution into the air.

Heating and cooling the millions of buildings in the United States require a lot of energy and have a huge impact on the environment.

South Florida Restoration Science Forum, U.S. Geological Survey

Buildings have a huge impact on the environment. There are more than 81 million buildings in the United States, according to the U.S. Department of Energy. Buildings consume more energy than any other economic category, including transportation and industry. Almost half of the energy that buildings use goes into heating and cooling.

Like Carmody, a growing number of engineers, planners, and architects have been looking for new ways to make buildings less wasteful and kinder to the environment. Improvements have come in many forms, including better insulation, windows, and construction materials.

Architects are also realizing that the size, location, and positioning of a building affects how much energy it uses. Even the arrangement of buildings in a neighborhood makes a difference.

“In the last 10 years,” Carmody says, “there has been a major movement toward what you’d call ‘green’ buildings.” Such buildings are sometimes also described as sustainable, environmentally friendly, or healthy.

Temperature control

The amount of energy you use for heating and cooling depends on where you live.

In places such as San Diego, Calif., for instance, the temperature is mild all year round. People rarely have to regulate the temperature of their homes.

Where I live in Minnesota, on the other hand, winters are unbearably cold, and summers can be unbearably hot. Without heaters and air conditioners, we’d be in big trouble. (At least, I know I would be pretty miserable.)

Transmission lines carry electricity from power plants to communities.

Oak Ridge National Laboratory

To get a sense of your own environmental impact, you can look at the climate where you live. Ask yourself how often you turn on the heater or the air conditioner, and how high you pump them up.

You might also want to figure out the source of the energy that your house or school uses for temperature control. Most air conditioners run on electricity. Some heaters do, too. If you find a furnace in the basement and radiators around your house, though, that probably means you have a system that burns natural gas or oil to heat water.

These energy sources have their downsides. Electricity, for example, usually comes from power plants that burn coal or use nuclear fuel. Both produce dangerous waste.

And there’s energy lost along the way. “Only about a third of the energy generated at a power plant makes its way to a house,” Carmody says.

One alternative energy source is to use wind to generate electricity.

U.S. Department of Energy

As an alternative energy source, harnessing the power of the wind or sun is becoming more popular in some places. Windmills for generating electricity are springing up from California to Germany. And researchers are working to make solar cells, which absorb light from the sun and convert it into electricity, more efficient.

Sunlight can also be used to heat tanks of water. Still, the technology needs some work. For now, solar power is more expensive than traditional sources. And some places don’t have enough reliable sunshine or wind to make these approaches practical.

Windows, walls, and roofs

No matter where the energy comes from to heat or cool your home, simple design and construction choices can have a big effect on how much energy you end up using.

First, consider when your home was built. Old houses tend to be drafty, Carmody says. They lose energy to the outdoors.

Newer buildings have more insulation packed into the walls. Fluffy materials such as fiberglass and Styrofoam have lots of pockets for trapping air. Such a structure holds heat in, just like a cozy sleeping bag. Many environmentalists prefer cellulose fiber, which is made from recycled paper and wood, for insulation.

When it comes to energy efficiency, windows are a big issue. Instead of just looking through them, take a closer look at the windows where you live. If you can feel cold air rushing in even when the window is closed, that’s a good sign that you’re wasting a lot of energy.

Researchers can monitor the energy efficiency of a wall and window combination.

Oak Ridge National Laboratory

New technologies are drastically improving window performance.

Windows used to be made from single sheets of glass. Today, windows are almost always double-glazed. This means there are two panes of glass set in a frame with an air space between them for insulation. Sometimes, windows are triple-glazed.

Scientists have also developed special coatings for windows. These invisible materials reflect heat. In a double-glazed window, coating the two sides of glass that face each other traps heat between the panes and increases insulation.

Chemists in England recently developed a kind of “smart” window coating. It reflects heat, but only when the window gets warmer than room temperature. If the technology becomes more affordable and practical, it could make windows even better at keeping the inside air in and the outside air out.

On the other side of the temperature fence, researchers from Oak Ridge and Lawrence Berkeley National Laboratories are working on a new type of roofing material that they hope will cut the cost of air conditioning by 20 percent.

At Oak Ridge National Laboratory, researchers test “cool-color” roofing materials, which reflect more sunlight than typical shingles or tiles do.

Oak Ridge National Laboratory

If you’ve ever worn a black T-shirt on a sunny day, you know that dark colors absorb light and create heat. Most roofs are dark, so they absorb infrared and visible light, which makes a building warmer. The idea is to make shingles with colors that reflect certain wavelengths of sunlight. Such “cool” roofs should be available in 3 to 5 years, the scientists say.

Living spaces

Perhaps the most innovative strategy for increasing energy efficiency actually has nothing to do with technology. Instead, architects take advantage of the environment and landscape to control temperature inside a building.

In the northern hemisphere, this can mean installing lots of south-facing windows so that plenty of sunlight can pour in. At the same time, well-designed overhangs keep summer sun out but let winter sun in.

Some people are choosing to live in communities that have been specifically designed to promote energy-efficient living. Village Homes in Davis, Calif., was one of the first of such green, or sustainable, developments.

Completed in 1981, the neighborhood has a network of paths that encourages people to bike or walk instead of drive (and pollute). The development’s 240 houses face south for lots of exposure to the sun. Overhangs provide shade. Houses run on solar power. There are lots of trees. And narrow streets have as little pavement as possible.

The strategy seems to be working. The air temperature around Village Homes is 15 degrees F. cooler than surrounding areas that have more pavement. And residents spend between one-third and one-half as much on energy bills compared to more conventional homes in nearby neighborhoods.

“We have a shadier, cooler microclimate,” says developer and resident Judith Corbett, who spoke at an environmental design conference in Minneapolis last April. “I don’t even have an air conditioner.”

As people see communities such as Village Homes thrive, these types of developments are becoming more popular. They’re springing up in places such as Colorado, Arizona, Virginia, and Australia.

Zero energy

The U.S. government itself is taking steps to boost the energy efficiency of the nation’s buildings. In one project, the Department of Energy has a long-term goal to create a “net-zero-energy” house—a house that wastes no energy.

In Tennessee, builders are putting up a house that should produce about as much energy as it uses. The roof and walls are made from special insulated panels, and solar cells on the roof generate electricity for the home.

Oak Ridge National Laboratory

The Department of Energy’s development of “near-zero-energy” homes is one step in that direction. One such house in Tennessee runs completely on electricity for just 82 cents a day. Conventional homes in the same area use between $4 and $5 in electricity a day.

As research on efficient energy use continues, think about what you can do to live a more energy-efficient life in the meantime.

Keep the heat low or off when you’re not home. Make sure leaks around doors and windows get patched. Turn off lights, TVs, and computers when they’re not needed.

Better yet, if you’re cold, put on a sweater and have a hot drink. If you’re hot, consider having an ice cream cone or going for a swim.

Going Deeper:

Word Find: Hot and Cold

Additional Information

Questions about the Article

Energy Facts

Energy use in the United States (Quadrillion Btu)

Btu, short for British Thermal Unit, is a unit of heat energy. One Btu is the amount of heat needed to raise the temperature of one pound of water 1° F. The heat given off by burning one wooden kitchen match is about 1 Btu.

Source: Energy Information Administration, U.S. Department of Energy