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Chewing on Some Science

INCREDIBLE EDIBLE SCIENCE By Tina L. Seelig, Illustrated by Lynn Brunelle Scientific American Books for Young Readers W. H. Freeman 80 pp., $19.95.

HOW do you make popcorn? In the microwave? In an air popper or an oil popper? Maybe you make it on the stove. Maybe you have even tried making it over a campfire.

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Every Sunday night, my brothers have ``movie night'' at their house, and they invite me and some friends over. We rent a movie and almost always make microwave popcorn.

One time I asked, ``What makes popcorn pop?''

``The kernels turn inside out to get some air,'' someone said.

``If you got that hot, you'd pop, too,'' someone else joked.

When I asked my three-year-old nephew if he knew why popcorn pops, he turned the table on me: ``I don't know. Why does popcorn pop?''

I decided I had better find the correct answer.

So I picked up the phone and called Tina Seelig.

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Dr. Seelig is a food scientist who lives near San Francisco, a city in California. When she was studying to be a scientist, she found that many of the things she did in the laboratory were the same kinds of things she did in the kitchen: measuring, mixing, heating, cooling, and more.

Soon, Dr. Seelig started asking herself scientific questions about food, and began searching for the answers. Then, she wrote two books about what she'd learned - one for adults and one especially for kids, ``Incredible Edible Science.''

In the book, Dr. Seelig explains the answers to such questions as: Why does water boil? Why do onions make you cry? Why does some fruit turn brown after you slice it? Why are hard-boiled eggs hard? She writes about solutions (a mixture in which one or more ingredients dissolve in a liquid) and chemical reactions. She also includes interesting experiments and tasty recipes to try.

``It's a tricky way of teaching kids that science exists in their everyday lives,'' Dr. Seelig says. ``The goal is to experience the thrill of discovery.'' In other words, it's cool to learn things you didn't know before.

Dr. Seelig's son, Josh, is five years old and loves to experiment in the kitchen. If he doesn't know the answer to a question, he and his mom will work on a hypothesis.

A what?

A hypothesis is sometimes called an ``educated guess'' - or a way to explain something after you've thought about it a lot.

When Tina and Josh Seelig come up with a hypothesis, they try to prove it with experiments.

Confused? Let's go back to the popcorn.

What if someone told you that there's a small amount of water inside each popcorn kernel? Since water turns to steam when it gets really hot and boils, you could guess - or form a hypothesis - that when the water inside the kernels turns into steam, the steam expands and blows up the kernels. Pretty neat, huh?

That hypothesis happens to be true.

Dr. Seelig often uses popcorn to teach kids about science in school. Once they find out that it's the water inside the kernels that makes popcorn pop, for example, they try different ways of making it. They soak some kernels in water first, and some they dry out. Some they just pop normally. Then, they compare their ``popped'' results.

Popcorn reacts to heat, but let's take a look at ice cream, which reacts to cold. Dr. Seelig says that ice cream contains just a few simple ingredients: cream, sugar, sometimes eggs, and flavorings such as vanilla or chocolate. But if you mix these ingredients together and stick them in the freezer, you don't get good ice cream. Why? The secret is in ice crystals and air bubbles.

Here are the three things that must happen to make good ice cream, Dr. Seelig writes:

* The water in the cream must freeze into tiny ice crystals. The crystals make the ice cream firm.

* The mixture must be whipped in order to mix in tiny air bubbles. The bubbles make the ice cream light.

* The fat in the cream must coat the ice crystals and the air bubbles. The fat makes the ice cream rich and creamy.

All this is just the beginning.

After you know about popcorn and ice cream, you may want to know why pickles are sour, what makes gravy lumpy, and what makes bread rise.

That reminds me: One time, a friend of mine decided to bake bread. Well, something went wrong, and the two loaves of bread did not ``puff up.'' Out of the oven came two hard bricks of bread - burned.

I asked Dr. Seelig how bread rises in the oven. Usually, the secret is carbon-dioxide gas - or bubbles - that results from yeast, baking soda, or baking powder reacting with the other ingredients in the batter. Those gas bubbles expand during baking and make the batter rise as it cooks.

Have you ever looked at a piece of bread to see where the bubbles might have been?

Here's a simple experiment you can try:

1. Take a zip-lock bag and put a couple of teaspoons of baking soda in it. Zip it almost shut (not all the way).

2. Add a few teaspoons of vinegar.

3. Now close the bag all the way and see what happens.

``You don't have to believe there's a reaction; you can see it,'' Dr. Seelig says. The temperature inside the bag will probably drop, and you'll see bubbles.

You can also try the same experiment using a bottle and a balloon. Put the baking soda in a small bottle and the vinegar in a balloon. Then attach the balloon to the end of the bottle and let the vinegar dribble into the bottle. Shake it up. The balloon should blow up a little. (Remember, if you're cooking or experimenting in the kitchen, let an adult help you.)

By solving cooking mysteries, you can learn a lot about science. ``It's very exciting when you know something other people don't,'' Dr. Seelig says. ``Knowing how the world works is power.''

If you have a food-science question that you can't find an answer to, you can write Dr. Seelig:

Tina L. Seelig, author of ``Incredible Edible Science, c/o W. H. Freeman and Company Publishers, 41 Madison Avenue, New York, NY 10010. Please include a self-addressed, stamped envelope.