You've learned a lot about the history of breakfast cereals here at Neatorama, and if you are in the New York area, you can see a part of that history. The Museum of Food and Drink in Manhattan will have one of the original puffing guns on display beginning August 17th. It was used in the mid-20th century to make puffed rice, wheat, and other grains. The gun was developed after puffed cereal was discovered accidentally.
In 1901, while attempting to determine the moisture content in a granule of starch, a botanist at the New York Botanical Garden, Alexander P. Anderson, filled hermetically sealed test tubes with cornstarch and wheat flour, and toasted the contents in a five-hundred-degree oven. Hit with a hammer, the still-hot tubes, which became pressurized as the temperature rose, exploded. The cornstarch, he found, had ballooned into a “porous puffed mass, white as snow” and nearly ten times its original volume, according to one account. Essentially, the water in the starch, unable to boil because of the hermetic seal, immediately vaporizes when the seal is released and the pressure drops; the steam expands outward and puffs the starch.
American cereal manufacturers use a more continuous puffing system now, but puffing guns are still made for use in other countries. However, only two men know how to make them, and when they are gone, so will puffing guns be gone. See the puffing gun in action in a video at The New Yorker. Link
(Image credit: General Mills)