The Science of Popcorn

THE SCIENCE OF POPCORN

Popcorn is a very special type of corn. It has a nonporous, tough outer hull that made of intense cellulose and arabinoxylan fibres which is the main reason for the “pop” sound. The unpopped dried corn kernel is composed of a starchy core and water droplets inside a dense, tough outer hull. The seed’s transformation into a crispy, fluffy popcorn requires a series of polymer transition steps consisting of heating, nucleation and popping, and expansion. 

Firstly, the seeds are exposed to heat. When the temperature exceeds 100°C during cooking, increased temperature causes the existing water inside the kernel to turn into steam. Because of the corn hull’s toughness and stronger crystalline structure enhanced by the help of increased temperature, formed steam can’t escape from the kernel, and internal pressure increases. Then, small bubbles form inside the endosperm and result in nucleation process. Also, starchy core cooks with heat. It undergoes gelatinization and crystalline melting by the interaction with the water vapor. The hull begins to rupture when the internal pressure exceeds the burst pressure of the hull and atmospheric pressure. With popcorn seeds at appropriate moisture contents around 11–15%, this explosion typically takes place when the internal kernel pressure is 760–930 kPa and internal kernel temperature is around 177–185°C. When the steam pressure reaches the critical value, the outer hull ruptures with a “pop” sound. The cooked starch erupts from the kernel in all directions by the help of the built-up steam. Expanded starch is also called as “starch bloom”. Just in seconds, the bloom structure turns into crispy, fluffy popcorn. 

Popcorn quality traits are categorized as expansion volume, unpopped kernels, hull dispersion, and the color, texture, and flavor of popped flakes. There are both intrinsic and extrinsic factors that affect these quality traits. The intrinsic factors can be listed as moisture content of the corn, kernel size, specific gravity, kernel sphericity, pericarp thickness, kernel damage, translucent and opaque endosperm, kernel lipids, and kernel proteins. The extrinsic factors are defined as heating methods, ingredient additions, and atmospheric pressure. However, one of the most important factor is the moisture content of the corn kernel. The optimum moisture value of each corn variety is different, although it is found that the optimum moisture content of the core for most variety is 13.0-14.5% to obtain the maximum expansion volume and for minimum unpopped kernel ratio. In order to protect this moisture content, popcorn seeds should be stored in an airtight container. 

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CONTENT: Gökçe Mavioğlu

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REFERENCES:

Gokmen, S. (2004). Effects of moisture content and popping method on popping characteristics of popcorn. Journal of Food Engineering, 65(3), 357-362. 

Lohner, S. (2016, August 18). Explore the "POP" in popcorn: A bursting science project. Retrieved from https://www.scientificamerican.com/article/explore-the-pop-in-popcorn/ 

Sweley, J. C., Rose, D. J., & Jackson, D. S. (2012). Quality Traits and Popping Performance Considerations for Popcorn (Zea mays Everta). Food Reviews International, 29(2), 157-177.