When corn kernels are put into a popcorn machine or pot, they are heated at a high temperature. With the increase of temperature, the water inside the corn kernels begins to vaporize and become water vapor. The volume of water vapor is much larger than that of water, so it will occupy more space and generate more pressure. This pressure will expand the shell and starch granules of corn kernels, and make corn kernels soft and gradually increase.
When the temperature of corn kernels reaches a certain critical value (about180 C), the shell of corn kernels will be unable to withstand the internal pressure and burst. At this time, the water vapor and starch gel inside the corn kernels will be released quickly, and the starch gel will quickly solidify into a film after contacting with air. In this way, the corn kernels become fluffy popcorn.
The Historical Origin of Popcorn
Popcorn is an ancient puffed food. Hundreds of years ago, before European immigrants moved into this "new continent", Indians living on this continent began to eat popcorn. After Columbus returned to Europe, he once described to people the vivid scene of Indian children in the "New World" selling popcorn in the street wearing necklaces. It was also the Indians who taught the new immigrants in Europe how to grow and bake corn.
A historian also found popcorn eaten by ancient Indians 5000 years ago in a cave in New Mexico, USA, but because of the "technology" at that time, the taste was far from crisp as that of popcorn of the times. Modern inventors designed an electric cooker for families who like popcorn. It is said that it only takes 10 minutes to make a large pot of popcorn.