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Pop Science

By Joy Hought, NS/S Research & Education Program Manager and Melissa Kruse-Peeples, Conservation Program Manager. Published on January 23, 2015.

The earliest varieties of maize must certainly have had small kernels as hard as glass.
– Edgar Anderson & Hugh Cutler, Races of Maize

In many ways, popcorn growing in a farmer’s field today is an anachronism: an organism that stubbornly belongs to another time, a time not only centuries past, but millennia. Small, glassy kernels on compact little cobs were the first identifiable domesticants to emerge from corn’s wild ancestor, teosinte (Zea mays ssp. parviglumis) and haven’t changed all that much in 8,000 years. Right here in our own back yard in the Tucson Basin, some of the oldest archeological evidence of corn in North America was found dating to over 4,000 years ago. This ancient corn was similar to the modern caramel brown Chapalote flint corn but was only an inch or two in length with a very thin cob, about the size of your pinky finger. The Chapalote race of maize is still used today for pinole as well as for popping but the last few centuries the variety now produces much larger ears.


A 1,000 year old maize from Tularosa Cave in southern New Mexico. National Museum of Natural History, Smithsonian Institution, Catalog number 246279.

The teosinte plant is only a few feet tall and very leafy, bushy and grasslike with lots of tillers (side shoots) that each produce tiny cobs; many modern popcorn plants are recognizable as a modern corn, but more often retain some old feral traits of teosinte: They are often shorter by a foot or two. They produce more tillers and more cobs. They don’t hold up very well to the intensity of modern hybrid corn farming – their stalks are weaker, they are sensitive to herbicides, and they don’t thrive with a lot of fertilizer. The seeds germinate and grow more slowly, another trait of undomesticated species.

So, the guilty pleasure that is popcorn is not a modern invention, but has been passed around in bowls for a really long time. Archaeologists suspect that popcorns naturally resulted from the traditional process of parching corn, and were subsequently selected for better and better popping. The laziest way to pop corn was simply by throwing it directly into a fire, or by heating it slowly in a vessel nearby. Corn was sometimes parched in hot sand, and we might get to try this tomorrow.


OlIa canchera, a prehistoric vessel used to parch maize. Image from Valcárcel (1934).


Starch composition in different corn classes. Image from Brunson & Richardson (1958), USDA Farmer’s Bulletin #1769.

Compared to other types of corn we eat – flour corns for making tortillas, dent corns for producing sugars - popcorn is classified as a type of flint corn, hard and vitreous, due to the endosperm. Popcorns aren’t a single race or subspecies, but exist as types within many races. It’s specifically that glasslike kernel that gives popcorn its pop: when exposed to heat the tightly packed starch granules in the endosperm will release their water content all at once, in a bang, rather than slowly dissipating. Popcorns also have the thickest pericarps among corns which helps pressurize the moisture. Popcorn producers have to take special care to make sure that the exact optimum amount of moisture is retained in the kernel - about 13.5% - otherwise, no blow. Heating kernels slowly and evenly produces the greatest volume: this allows all of the starch inside the kernel to reach the right point at the same time. This site is a good resource for troubleshooting popping.

Expansion in popcorn kernels is a great example of what geneticists call a quantitative trait – to understand this, think of quantity, and of a trait that can be described in terms or how much of it is expressed in the phenotype; examples in humans are things like height and intelligence. These are traits affected by identifiable genes, but genes that interact with each other and with the environment in complex ways. In human traits we talk about nature versus nurture; and agronomists and plant breeders often speak of genotype-by-environment interactions. How much popcorn pops is due to 4 or 5 major genes, to growing environment, to handling and processing, and what researchers get to call the genotype-by-popping-method interaction. That is, some varieties pop better with hot oil, some with hot air, and some in the microwave – which has led to different strains of hybrid popcorns for each industry niche, with, you probably guessed it, microwave-loving genotypes dominating the market today.

Genetics also plays a big role in the type of “flake” that is produced. “Butterfly” flakes are more tender and crunchy, and tend to be preferred by the people who munch on them; larger “mushroom” flakes are chewier but are preferred by industry, which has a different aim: to get the popped thing to stay intact through processing, packaging and shipping until it reaches the people who munch on them.

Hungry yet?

Below are some of the coolest popcorns we conserve in the Native Seeds/SEARCH Seed Bank.

Reventador. Our most highly recommended variety for popping. It is very flavorful, hardy, and crunchy. Consistent and high volume expansion of the kernels – hence its name, which can be translated as “the exploder”. This variety is from central Sonora and has some day-length sensitivity (it will flower late in the summer) so it is not recommended for northern latitudes. Tall variety with plants reaching 9 feet.

Tarahumara. Very similar to Reventador. Great popping qualities, flavor, and texture. Extremely tall!

Chapalote. A specific variety, but also a race of corn that is considered to be one of the oldest known, with archaeological evidence of use dating 2,000 BC in the lowland areas of northwest Mexico and the American Southwest. NS/S conserves over a dozen Chapalote accessions including brown, white, and yellow variants. Deep chocolate brown is the most typical and is revered for making pinole, a toasted ground corn with a strong nutty flavor that is added to drinks and baked goods. Recently Chapalote is seeing a revival and is sought after for making polenta. Chapalote can also be popped with varying results. It is day-length sensitive and is not recommended for northern latitudes.

Navajo Copper. This has to be one of the cutest varieties! Plants are less than waist-high and produce several ears each. The color of this popcorn spans the colors of southwestern sunsets so it is beautiful to grow, but the flavor and texture as a popcorn are recommended as well. Fast maturing.


Flor del Rio (above). A multi-colored variety with moderate kernel expansion and good flavor and texture. One interesting quality is that it produces many plants with deep purple stalks and husks. Plant height is around 6-7 ft. Recent nutritional analysis of maize from the NS/S collection produced results that Flor del Rio (along with Chapalote Pinole Maiz) contained the highest concentrations of health-promoting carotenoid and anthocyanin pigments.

Tarahumara Epachi. An absolutely gorgeous variety with pearly white kernels and occasional lavender and dark purple shades. Similar popcorn qualities to the Reventador varieties but is faster maturing and has much shorter plants (5-6’).

Glass Gem. Arguably Glass Gem is one of the world’s best know popcorn varieties. It was bred for its aesthetics of highly translucent, gem-like kernels. Therefore the popping quality plays second string. There is a large variation in kernel size but the small and medium sized kernels do have moderate expansion. Flavor reports are quite positive and people have made Glass Gem into popcorn and cornmeal to use in breads and grits. Grows in a diversity of climates.

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