In a great article and video for The New Yorker’s Elements blog, Sky Dylan-Robbins and Matt Buchanan take a look at the technology and history behind puffed breakfast cereal.
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.