The secrets of popcorn

Updated: Dec 20, 2019

The relationship between popcorn and cinema is inseparable. Maybe without this crispy snack, the cinema would not be as we know it. Today popcorn reveals its secrets.

In the mid-nineteenth century, popcorn was already settled in the American diet but until the early 1930s, there was no boom in its consumption.

At the beginning theatres and cinemas banned its consumption. The fact that the cinema, at that time, was mute and the popping noise of the snack could distract the audience, discourage the owners of the cinemas to allow their consumption.

With the arrival of the sound cinema in 1927, its success was greater but until the Great Depression in 1929, there was no significant growth in its consumption.

The low price of the popcorn together with the fact that the cinema was the only entertainment of the average citizen, finished joining these two. Entrepreneurs began to install their popcorn machines at the doors of cinemas. The popularity of popcorn was progressively increasing and the cinemas started allowing to sell them in their rooms. As the benefits increased, the cinemas decided to eliminate the intermediaries and set up themselves their popcorn stands. The popcorn business was already rolling!.

If you want to know more information about its history, this blog is amazing!.

The physics behind popcorn

When the corn seed is heated, it behaves like a miniature pressure cooker. There are many varieties of corn capable of exploding when heated but the ideal one is Zea mays everta due to it has a higher proportion of translucent starch (where it accumulates from 12% to 14.5% of the humidity, necessary to produce the increase in pressure within of the grain).

Other corn seeds also produce popcorn but the proportion of unexploited seeds and especially their low expansion when heated makes them commercially unfeasible.

Popcorn can be expanded from 20 to 40 times the original volume of the seed!

The detailed mechanism of popcorn production was proposed in 1983 by Hoseney, Zeleznak and Abdelrahman. This model explains that the pericarp acts as a barrier to the increase in pressure that the seed undergoes when it is heated.

When the seed is heated between 170°C and 180°C, the gases contained within the grain begin to expand, then the water retained in the translucent starch begins to vaporize but due to the high pressure it reaches inside the grain, most of it remains as superheated water.

When the pressure inside the grain reaches 8 atm, the pericarp fails and breaks the outer layer of the grain, facilitating the exit of the gases. At this time, the starch is in a gelled state and when the internal pressure is equal to the atmospheric one, the superheated water suddenly vaporizes producing an expansion of the starch.

This rapid expansion of starch produces cooling of the starch, solidifying it and producing the "sponge" effect of the popcorn. Its appearance at this time is irregular and white.

The increase in the volume of the popcorn is approximately 30 times its original size. This expansion is adiabatic because the speed of the expansion does not allow the starch to exchange heat with the air around it and seeks balance with the environment.

The expansion ends when the pressure generated in the seed is balanced with the atmospheric pressure. This expansion determines the size of the popcorn, but is it possible to increase the size of the popcorn? The answer is yes. By modifying the pressure surrounding the seed, larger popcorn can be achieved!

Dr Daniel Hong of Lehigh University in Pennsylvania studied the effect of pressure in the increase of the volume of popcorn and he demonstrated that the pressure increases the size of popcorn and reduces the percentage of unexploded popcorn. Cool!

Corn seed contains many secrets. Did you ever imagine that a simple grain of corn contains so much chemistry and physics? I hope that after knowing all this, popcorn is no longer a simple snack that accompanies a good movie. Enjoy.