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What Makes Popcorn Pop?

Poppin PopcornThe Science of Popcorn

People have been fascinated by popcorn for centuries.  Some Native Americans believed that a spirit lived inside each kernel of popcorn.  When heated, the spirit grew angry and would eventually burst out of its home and into the air as a disgruntled puff of steam.  A less charming but more scientific explanation exists for why popcorn pops. 

Popcorn is scientifically known as Zea mays everta.  It’s a type of maize, or corn, and is a member of the grass family.  Popcorn is a whole grain and is made up of three components: the germ, endosperm, and pericarp (or hull).  Of the 4 most common types of corn—sweet, dent (also known as field), flint (also known as Indian corn), and popcorn—only popcorn pops!  Popcorn differs from other types of corn in that its hull has just the right thickness to allow it to burst open.

Each kernel of popcorn contains a small drop of water stored inside a circle of soft starch. Popcorn needs between 13.5-14% moisture to pop.  The soft starch is surrounded by the kernel's hard outer surface.

As the kernel heats up, the water begins to expand.  Around 212 degrees the water turns into steam and changes the starch inside each kernel into a superhot gelatinous goop.  The kernel continues to heat to about 347 degrees.  The pressure inside the grain will reach 135 pounds per square inch before finally bursting the hull open.

As it explodes, steam inside the kernel is released.  The soft starch inside the popcorn becomes inflated and spills out, cooling immediately and forming into the odd shape we know and love.  A kernel will swell 40-50 times its original size!