Corn

Categories: Agriculture; economic botany and plant uses; food

Corn (Zea mays), also called maize, is a coarse, annual plant of the grass family (Poaceae, also called Gramineae). It ranges in height from three to fifteen feet and has a solid, jointed stalk and long, narrow leaves. One stalk usually bears one to three cobs, which develop kernels of corn when fertilized. Corn no longer grows in the wild; it requires human help in removing and planting the kernels to ensure reproduction. In the United States and Canada, “corn” is the common name for this cereal, but in Europe, “corn” refers to any of the small-seeded cereals, such as barley, wheat, and rye. “Maize” (or its translation) is the term used for Zea mays in Europe and Latin America.

Historians believe that an early form of corn was originally domesticated in what is now Mexico. Explorer Christopher Columbus brought corn kernels back to Europe with him in 1493, and within one hundred years it had spread through Europe, Asia, and Africa. Corn grows as far north as Canada and Siberia (roughly 58 degrees north latitude) and as far south as Argentina and New Zealand (roughly 40 degrees south). Although adaptable to a wide range of conditions, corn does best with at least twenty inches of rainfall (corn is often irrigated in drier regions) and daytime temperatures between 70 and 80 degrees Fahrenheit (about 24 degrees Celsius). Much of the United States meets these criteria, hence its ranking as the top corn-producing country in the world.

Origins and Hybridization

Corn’s exact origins remain uncertain, but archaeological records suggest the gathering of a wild precursor to corn, called teosinte, began in ancient Mesoamerica sometime between 12,000 BCE and 8000 BCE. Domestication began around 7000 BCE, if not earlier; through a combination of genetic mutation and selective planting, teosinte evolved relatively quickly into a primitive type of corn, with tiny cobs containing just eight rows of kernels. Experimentation by geneticist George W. Beadle in the latter half of the twentieth century revealed that just five or so genes were responsible for the differences between teosinte and this early corn. The fossil record shows a marked change in corn by 3400 BCE, notably increased cob and kernel size, indicating greater domestication. Fully domesticated corn (which could not survive without human help) had replaced the wild and other early types of corn by 700 CE.

Extensive attempts at hybridization began in the late nineteenth century, but the increase in yield was usually a disappointing 10 percent or so. By 1920 researchers had turned to inbreeding hybridization programs, in which the corn was self-fertilized rather than being allowed to cross-pollinate naturally. Following a complex sequence of crossing and testing different varieties, the lines with the most desirable traits were put into commercial use, and they often produced 25 to 30 percent gains in yield. Although these early hybrids focused on increasing the yield, researchers later began to look for insect-resistant and disease-resistant qualities as well. One of the hybridizers of the 1920s was Henry A. Wallace, founder of Pioneer Seed Company (the world’s largest seed company) and later US vice president under Franklin D. Roosevelt. By the 1950s hybrid corn varieties were in widespread use.

Types and Uses

There are six major types of corn still in use: dent corn, flint corn, flour corn, sweet corn, pod corn, and popcorn. Dent corn, characterized by a “dent” in the top of each dried kernel caused by the shrinking of soft starch, is the most important commercial variety. Flint corn contains little to no soft starch and tends to be resistant to the rots and blights known to attack other types; it is also more tolerant of low temperatures and therefore appears at the geographical edge of corn’s range. Flour corn is known for the soft starch in its kernel, which makes it easier to grind into flour and thus popular for hand-grinding. Sweet corn has a higher sugar content than other types of corn, because most of the sugars in its kernel are not converted to starch; as a result, it does not store well and is best eaten fresh from the cob. Pod corn, the most primitive type of corn and one of the oldest, has little commercial value and is primarily grown for research purposes. Finally, popcorn, a mainstay at American movie theaters and as a snack food, has an optimum moisture content of about 13 percent and will explode to as much as thirty times its original volume when heated.

Commercially, corn is used mostly for livestock feed and industrial processing. It is high in energy and low in crude fiber but requires supplements to make a truly good feed. Industrial processing creates a great variety of products found in everyday life—underscoring the importance of corn to the world’s economy. In addition, corn is increasingly being used as feedstock for corn ethanol, a biofuel, and for biogas production.

Industrial processing of corn takes place in one of three ways: wet milling, dry milling, or fermentation. In wet milling, corn is soaked in a weak sulfurous acid solution, ground to break apart the kernel, and then separated. The resulting by-products are found nearly everywhere. The cornstarch supplies corn syrup (it is sweeter than sugar and less expensive, and billions of dollars’ worth is produced for soft-drink manufacturers each year), starches used in the textile industry, ingredients for cooking and candymaking, and substances used in adhesives, to name a few. Other by-products provide cooking oil; oil used in mayonnaise, margarine, and salad dressing; soap powders; and livestock feed. Dry milling is a simpler process, involving the separation of the hull from the endosperm (the food storage organ, which is primarily starch in most corn) and the germ (the plant embryo) by repeated grinding and sieving. Dry milling produces hominy, grits, meal, and flour, all of which are used for human consumption. Fermentation of corn changes the starch to sugar, which is then converted by yeast to alcohol. The process eventually results in ethyl alcohol, or ethanol (which can be blended with gasoline to reduce carbon monoxide emissions or used in higher concentrations as an alternative fuel for specially designed vehicles), acetone, and other substances.

Bibliography

Carroll, Sean B. “Tracking the Ancestry of Corn Back 9,000 Years.” The New York Times, 24 May 2010, www.nytimes.com/2010/05/25/science/25creature.html. Accessed 20 Apr. 2017.

“Evolution of Corn.” Learn.Genetics, Genetic Science Learning Center, U of Utah, 1 July 2013, learn.genetics.utah.edu/content/selection/corn/. Accessed 20 Apr. 2017.

Hardeman, Nicholas P. Shucks, Shocks, and Hominy Blocks: Corn as a Way of Life in Pioneer America. Louisiana State UP, 1981. Addresses the often-overlooked period between the early domestication of corn and its modern improvements.

Johannessen, Sissel, and Christine A. Hastorf, editors. Corn and Culture in the Prehistoric New World. Westview Press, 1994. A collection of twenty-eight essays that examine the relationships between corn and people in the Americas from perspectives of archaeology, anthropology, genetics, linguistics, and biochemistry.

McCann, James. “Maize and Grace: History, Corn, and Africa’s New Landscapes, 1500–1999.” Comparative Studies in Society and History, vol. 43, no. 2, 2001, pp. 246–72. McCann chronicles the historical advance of corn in Africa since its introduction around 1500 and delineates different histories of change through three different areas of its advance.

Mangelsdorf, Paul C. Corn: Its Origin, Evolution, and Improvement. Belknap P of Harvard UP, 1974. Offers a thorough and balanced discussion of the different theories of corn’s origins, with good illustrations.

Plaisted, Susan McLellan. “Corn.” The Oxford Encyclopedia of Food and Drink in America, edited by Andrew F. Smith, 2nd ed., Oxford UP, 2013, pp. 552–56.

Piperno, Dolores R. “The Origins of Plant Cultivation and Domestication in the New World Tropics: Patterns, Process, and New Developments.” Current Anthropology, vol. 52, no. S4, 2011, pp. S453–70. Academic Search Complete, search.ebscohost.com/login.aspx?direct=true&db=a9h&AN=66998650&site=ehost-live. Accessed 20 Apr. 2017.

Sprague, George F., and John W. Dudley, editors. Corn and Corn Improvement. 3rd ed., American Society of Agronomy, 1988. Provides articles on all aspects of corn, including history, genetics, cultivation, and uses.

Wallace, Henry A., and William L. Brown. Corn and Its Early Fathers. Rev. ed., Iowa State UP, 1988. Focuses on the individuals who contributed to the improvement of corn.