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Pop-Ability of the Popcorn

Daksha Shah 6

Popcorn is the favorite snack whether you are in a theatre or a carnival or at home.

The site of watching these corn kernels pop inside that closed glass case is blissful.

Nowadays these come in a wide range of flavors too, like butter, pepper, caramel etc.

No, wonder movies seem incomplete without a bucket full of palatable popcorn to satisfy your taste buds. 

But, have you ever thought why and how these little fluffy snacks pop? The reason must be unknown to many. Let us find out the mystery behind the popping corns. 

The kernel structurepk

Popcorn is actually the cultivated strain of flint corn known as Zea mays everta. 
The yellow kernel of the corn has a unique structure. It is made of 3 main parts – the pericarp, germ, and endosperm.
Pericarp – It is the tough outer shell that surrounds the kernel. This shell is also known as the hull and is the impervious protective layer around the germ and the endosperm. The hull is what makes the distinctive popping sound.
Endosperm – contains the food for the germ when it sprouts. It contains starch and some trapped water. The optimum amount of water for a good popcorn is around 13-14%. 

3. The germ is the “embryo” that germinates into a plant. 

The reason behind the pop

pk11. As the kernel is heated up, the small amount of water trapped inside the endosperm too gets heated. 

2. The heat converts the water into steam. The expansion ratio between water in its liquid form and steam is about 1:1700. This means that under ideal conditions, 1 part of liquid water expands to 1700 times the volume of steam when boiled. The expanded steam creates enormous pressure inside the kernel. The strong pericarp shell is able to retain this pressurized steam up to 9.2 atm pressure (135 psi).

3. The pressurized and super-heated steam converts the starch of the endosperm layer into a gelatinous material. 

4. The pressure continues to increase until the breaking point of the hull is reached: a pressure of about 135 psi (930 kPa and a temperature of 180 °C (356 °F). As this point, the strong Hull gives in and bursts, letting out the popcornsteam and making the characteristic pop sound. A typical kernel of popcorn once it pops will complete the popping/expanding process in less than 1/50th of a second. The resulting popped kernel is 40 to 50 times its original size.

5. As the hull bursts, the gelatinized starch also expands and cools down rapidly to form fluffy flakes of corn that we relish. The jelly bubbles of starch that formed due to heating fuse together and quickly solidifies on cooling on exposure to air.  The cooling sets the starch and the protein polymers into the white puffy flakes.

8mrvwGood popcorn 

Three main elements of popcorn together are required to produce popcorn kernels that are good for popping.  Those three elements are: 

1. The percentage of water content – The ideal water content is around 13.5%, with the typical bursting point at around 350-450 degrees.
2. Hard, undamaged, water impermeable shell is required to survive the increasing pressure until the starch gets gelatinized.
3. A starchy center – to produce the fluffy flake.


“Butterfly” and “Mushroom” are the two varieties of popcorn flakes that you usually get.
Butterfly” or “snowflake” flakes are irregular in shape and have a number of protruding “wings”.
A mushroom kernel is round in shape like a baseball, perfectly suited for coatings of caramel, cheese, or even chocolate.

Popping Pitfalls

mushroom-popcorn-kernels-2Faulty hull – If the hull is cracked or porous, it allows the steam to escape. Hence, enough pressure is not built to pop the corn. 

Low moisture content – Without enough water there is less of steam formed. Less steam is unable to create the required pressure for the pop.

Cooking style – Heating the kernel too quickly will not give the starch inside it enough time to gelatinize and hence flake less.  If heated too slowly, the shell may form cracks and let the steam escape and the corn may not pop at all.   

Next time, you prepare or order popcorn you can boast of knowing the science behind the delicious snack. 

Daksha Shah

Daksha is an integral part of the editorial team at Zigya. Armed with a B.Tech degree, she oversees content quality assurance for Biology. Her subtle wit, observation skills and agile demeanour bring the buzz in the editorial team and ensures meeting stiff deadlines. An astute blogger, when not working Daksha prefers to spend her time with her canine companion, Spiky. Follow her work at

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