How popcorn pops or does not pop – some new ideas

How does popcorn pop? Why is it that other grains don’t pop?

Wikipedia entry on popcorn says:

As with all cereal grains, each kernel of popcorn contains a certain amount of moisture in its starchy endosperm. Unlike most other grains, the outer hull, or pericarp, of the popcorn kernel is thick and impervious to moisture.

As the kernel is heated past the boiling point, water in the kernel begins to turn to steam, generating an internal pressure of about 9 atm. In kernels of other grains (and in damaged kernels of popcorn), this steam escapes as fast as it forms, but in the tightly sealed popcorn kernel, the steam is held tight by the pericarp and the pressure starts to build until the pericarp suddenly ruptures, causing a small explosion. The force of the explosion turns the kernel inside out. More importantly, because the moisture is evenly distributed throughout the starchy endosperm, the sudden expansion turns the endosperm into an airy foam which gives popcorn its unique texture.

Two explanations exist for kernels which do not pop, known in the popcorn industry as “old maids,” after being exposed to high temperatures. The first is that unpopped kernels do not have enough moisture to create enough steam for an explosion. The second explanation, according to research led by Dr. Bruce Hamaker of Purdue University, is that the unpopped kernel may have a leaky hull.


I was wondering about this leaky hull theory and while browsing the Chemistry World magazine from the Royal Society of Chemistry, I found this really interesting explanation:

The secret to maximising pop-ability lies in the chemistry of the corn kernel, says Hamaker. He has identified a
crystalline structure in popcorn that appears to determine popping success. His team tested a variety of popcorn
brands, and found the most poppable ones share a characteristic chemical structure of the outer hull (pericarp).

The data suggest that cellulose in the pericarp is responsible for the development of exothermal events and increased crystallinity. ‘The propensity of cellulose to form crystalline structures in the popcorn pericarp during microwave heating improves moisture retention and hence popping performance,’ they write. Improving pop-ability – by breeding varieties with optimal crystalline structure; by chemical modification of corn kernels; or by genetic modification – could result in a better product in three to five years, predicts Hamaker.

So, the perfectly popping popcorn is not too far off in the future. Can’t wait.