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Guide Index

A Feast at Plimoth

Feast or Famine

Truth or Consequences


Mushroom Mania

The Bite Stuff
in the classroom


Our very survival can be traced back to three regions of the world, where people living thousands of years ago figured out how to optimize the nutritional value of three basic foodstuffs -- corn, wheat and soy. Frontiers travels to New Mexico to find out how Native Americans unlock the essential vitamins in blue corn. Next, anthropologist Solomon Katz demonstrates how the Chinese transform the toxic soybean into a nutritious protein and how the chemistry of yeast turns wheat into bread.

Curriculum Links
Activity 1: Pop Goes the Kernel
Activity 2: Testing for pH: Acid-base Mini-lab
Math Challenge
More About Corn




acids and alkalis,
equations, reactions,
percent composition problems

ecosystems, minerals


plants as food


cooking methods,

Middle East


As you see on Frontiers, corn has been a key food in the Americas for thousands of years, but with the advent of microwave popcorn, we lost the experience of watching corn kernels pop. This popcorn lab helps enhance your observational, measuring and mathematical skills in a fun and tasty way!

Why do corn kernels pop? A large percentage of the composition of the kernel is water. As a corn kernel is heated, the water inside it increases in temperature. As the temperature rises, the pressure in the kernel increases, causing the kernel to burst open and form a piece of "popped corn."

With this lab, you will observe the popping corn and measure differences in the mass of the corn before and after heating.

  • hot plate
  • goggles
  • balance
  • cooking oil
  • 400ml beaker
  • container for massing popcorn
  • beaker tongs or a hot mitt
  • tin foil (for lid)
  • unpopped corn kernels

  1. Set up the hot plate and beaker.

  2. Record the mass of the empty beaker in the data table.

  3. Mass approximately 8g of popcorn in a container. (Don't forget to tare the balance. If you don't have an electronic balance, subtract the mass of the corn from the total mass of container plus corn.) Record the exact mass in the data table.

  4. Place 5ml of oil into the beaker, mass and record in the data table.

  5. Add corn and place a 10cm x 10cm foil cover on the beaker. Place the beaker on the hot plate, and slowly and carefully heat the corn. Use beaker tongs or a hot mitt to shake the beaker as the corn cooks. Record all observations (volume changes, condensation in beaker, detection of corn odor, etc.). Cook corn until as many kernels pop as possible without burning the corn.

  6. Remove the cover and allow the beaker to cool. Mass and record in the data table.

  7. If you are using food-safe glass, eat and enjoy!


 empty beaker  
 unpopped corn  
 beaker and oil  
 beaker, oil, and popped corn  

  1. Find the mass of the oil.

  2. Find the mass of the beaker, oil and unpopped corn.

  3. Find the difference in mass of the beaker, oil and corn before and after popping.

  1. What happened to the mass of popcorn after popping?

  2. What happened to the volume of popcorn during popping?

  3. Is it necessary to use oil when making popcorn? Explain.


As you saw on Frontiers, when lime water, a basic solution, is added to blue corn batter, an acidic mixture, the batter turns a particular shade of blue as it reaches the desired pH. The Native Americans who made piki bread did not realize it, but they were conducting an acid-base experiment. The blue corn acts as an indicator that changes to a different shade of blue as the batter becomes more basic (lime water equals calcium hydroxide Ca(OH)2). (You may want to review the definitions below before doing this activity.)

In this activity, you will make your own indicators using fruit, flowers or vegetables. The indicators become different colors in acidic or alkaline conditions.

  • fruit, vegetables (apples, plums, peaches, blueberries, strawberries, raspberries, onions, beets, etc.)
  • containers for boiling fruit and vegetables
  • 2 dropper bottles: one filled with an acidic solution (vinegar, weak hydrochloric acid) and one with a basic solution (ammonia, weak sodium hydroxide)

  1. Pick a fruit or vegetable that you want to test. Peel it. Place peels in water (enough water to cover).

  2. Boil the peels for 3 to 5 minutes to make a colorful juice. (You can do this in small beakers on a hot plate.) Repeat for each fruit and/or vegetable that you want to test.

  3. Cool the juice. Once cool, place two separate drops of juice on filter paper.

  4. Place one drop of the acid solution on the first drop of juice and one drop of the basic solution on the second drop. The juice will indicate one color under the acidic conditions and another color under basic conditions. Each fruit or vegetable indicator will react differently with the acid/base samples. For example, blueberries will indicate red in an acidic solution and blue in a basic solution. (You can also try this activity with flower petals.)


ACID: a substance that produces hydrogen ions in water solution. An acid donates protons (hydrogen ion equals H+).

BASE: an alkaline substance that produces hydroxide ions in water solution. A base is a proton acceptor (hydroxide ion equals OH-).

INDICATOR: a weak organic compound that is used to indicate the pH of a solution by a color change.

pH SCALE: a logarithmic scale expressing degree of acidity or basicity. A pH of 0 to 7 is acidic; a pH of 7 is neutral (distilled water); a pH of 7 to 14 is basic (or alkaline). Some common pH values: lemon juice equals 2.2 to 2.4; ammonia equals 11.


Cabbage juice acts as a unique indicator -- you can create an entire spectrum of colors if you add the juice to a series of solutions ranging in pH from 1 to 14. Follow the same procedure as above to make the cabbage indicator. Use a pH meter if you wish to choose solutions with varying pH values. Next, add the cabbage juice indicator to each solution. You should see a rainbow of colors with each change in pH. Make your own indicator paper by dipping filter paper into cabbage juice. Hang the paper to dry, then use it to test as you would universal indicator paper.


What's the best buy on popcorn? To find out, first convert to decimals.
A 7-oz. bag for $2.39
A 2 3/8-oz. bag for $.99
A 5/8-oz. bag for $.25
A 1-oz. bag for $.75

  • Many Native Americans enjoyed popcorn for thousands of years before Europeans landed on the shores of the New World. Chief Massasoit's brother, Quadequina, brought popcorn ("parched corn") to the first Thanksgiving feast.

  • Corn played an important role in cultures in Central and North America, not only as a significant food but as part of religious ceremonies for the Incas, Mayas, Aztecs and many Native American tribes. Find out more about the Green Corn ceremonies practiced by various tribes.

  • Tiny fossil popcorn cobs that dated back 7,000 years were discovered in New Mexico's Bat Cave in 1948. The find gave botanists a clue to the origins of corn, which derives from a wild grass, teosinte. How many products and foods can you list that contain corn?

  • To the Hopi, yellow corn symbolized the north; blue, the west; red, the south; and white, the east. Purple corn stood for the sky; gray stood for the underworld.


Scientific American Frontiers
Fall 1990 to Spring 2000
Sponsored by GTE Corporation,
now a part of Verizon Communications Inc.