十万个为什么·科学启蒙30篇（2）

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爆米花为什么会爆开？

Popcorn kernels contain a small amount of water sealed inside a hard, moisture-proof hull — usually about 13–14% by weight.
When heated, the water turns to steam and builds pressure inside the kernel until the hull ruptures at around 175°C and 9 atmospheres.
The sudden release of steam causes the starchy interior to expand rapidly, cool, and solidify into the fluffy white shape we recognize.
Only certain corn varieties pop well because their hulls are strong enough to hold pressure but thin enough to burst cleanly.
Kernels that don’t pop — called 'old maids' — either lost moisture over time or have tiny cracks letting steam escape slowly.
Microwave popcorn works because the bag traps steam and heat, but overheating can burn kernels or release harmful fumes from artificial flavorings.
Ancient civilizations in Peru and Mexico cultivated popcorn over 7,000 years ago, long before modern cooking methods existed.
Each kernel pops with a small 'explosion' that produces a distinctive snap — audible up to 3 meters away in quiet conditions.