Sweet corn (Zea mays convar. saccharata var. rugosa; also called sugar corn and pole corn) is a variety of maize with a high sugar content. Sweet corn is the result of a naturally occurring recessive mutation in the genes which control conversion of sugar to starch inside the endosperm of the corn kernel. Unlike field corn varieties, which are harvested when the kernels are dry and mature (dent stage), sweet corn is picked when immature (milk stage) and prepared and eaten as a vegetable, rather than a grain. Since the process of maturation involves converting sugar to starch, sweet corn stores poorly and must be eaten fresh, canned, or frozen, before the kernels become tough and starchy.
|Nutritional value per 100 g (3.5 oz)|
|Energy||360 kJ (86 kcal)|
|Dietary fiber||2.7 g|
|Aspartic acid||0.244 g|
|Glutamic acid||0.636 g|
|Vitamin A equiv.||
One ear of medium size (6-¾ to 7-½ inches long) maize has 90 grams of seeds
|Percentages are roughly approximated using US recommendations for adults.
Source: USDA Nutrient Database
Sweet corn occurs as a spontaneous mutation in field corn and was grown by several Native American tribes. The Iroquois gave the first recorded sweet corn (called Papoon) to European settlers in 1779. It soon became a popular food in southern and central regions of the United States.
Open pollinated varieties of white sweet corn started to become widely available in the United States in the 19th century. Two of the most enduring varieties, still available today, are Country Gentleman (a Shoepeg corn with small, white kernels in irregular rows) and Stowell's Evergreen.
Sweet corn production in the 20th century was influenced by the following key developments:
- hybridization allowed for more uniform maturity, improved quality and disease resistance
- identification of the separate gene mutations responsible for sweetness in corn and the ability to breed varieties based on these characteristics:
- su (normal sugary)
- se (sugary enhanced, originally called Everlasting Heritage)
- sh2 (shrunken-2)
There are currently hundreds of varieties, with more constantly being developed.
The fruit of the sweet corn plant is the corn kernel, a type of fruit called a caryopsis. The ear is a collection of kernels on the cob. Because corn is a monocot, there is always an even number of rows of kernels.[further explanation needed] The ear is covered by tightly wrapped leaves called the husk. Silk is the name for the pistillate flowers, which emerge from the husk. The husk and silk are removed by hand, before boiling but not before roasting, in a process called husking or shucking.
In most of Latin America, sweet corn is traditionally eaten with beans; each plant is deficient in an essential amino acid that happens to be abundant in the other, so together sweet corn and beans form a balanced diet. In Brazil, sweet corn cut off from the cobs is generally eaten with peas (where this combination, given the practicality of steamed canned grains in an urban diet, is a frequent addition to diverse meals such as salads, stews, seasoned white rice, risottos, soups, pasta, and, most famously, whole sausage hot dogs).
Similarly, sweet corn in Indonesia is traditionally ground or soaked with milk, which makes available the B vitamin niacin in the corn, the absence of which would otherwise lead to pellagra; in Brazil, a combination of ground sweet corn and milk is also the basis of various well-known dishes, such as pamonha and the pudding-like dessert curau, while sweet corn eaten directly off the cobs tends to be served with butter.
The kernels are boiled or steamed. In Europe, China, Korea, Japan and India, they are often used as a pizza topping, or in salads. Corn on the cob is a sweet corn cob that has been boiled, steamed, or grilled whole; the kernels are then eaten directly off the cob or cut off. Creamed corn is sweet corn served in a milk or cream sauce. Sweet corn can also be eaten as baby corn.
If left to dry on the plant, kernels may be taken off the cob and cooked in oil where, unlike popcorn, they expand to about double the original kernel size and are often called corn nuts. A soup may also be made from the plant, called sweet corn soup.
Open pollinated (non-hybrid) corn has largely been replaced in the commercial market by sweeter, earlier hybrids, which also have the advantage of maintaining their sweet flavor longer. Su varieties are best when cooked within 30 minutes of harvest. Despite their short storage life, many open pollinated varieties such as Golden Bantam remain popular for home gardeners and specialty markets, or are marketed as heirloom seeds. Although less sweet, they are often described as more tender and flavorful than hybrid varieties.
Supersweet corn are varieties of sweet corn which produce higher than normal levels of sugar developed by University of Illinois at Urbana–Champaign professor John Laughnan. He was investigating two specific genes in sweet corn, one of which, the sh2 gene, caused the corn to shrivel when dry. After further investigation Laughnan discovered that the endosperm of sh2 sweet corn kernels store less starch and from 4 to 10 times more sugar than normal su sweet corn. He published his findings in 1953, disclosing the advantages of growing supersweet sweet corn, but many corn breeders lacked enthusiasm for the new supersweet corn. Illinois Foundation Seeds Inc. was the first seed company to release a supersweet corn and it was called Illini Xtra Sweet, but widespread use of supersweet hybrids did not occur until the early 1980s. The popularity of supersweet corn rose due to its long shelf life and large sugar content when compared to conventional sweet corn. This has allowed the long-distance shipping of sweet corn and has enabled manufacturers to can sweet corn without adding extra sugar or salt.
The third gene mutation to be discovered is the se or "sugary enhanced" allele, responsible for so-called "Everlasting Heritage" varieties, such as Kandy Korn. Varieties with the se alleles have a longer storage life and contain 12–20% sugar compared to su varieties.
All of the alleles responsible for sweet corn are recessive, so it must be isolated from any field corn varieties that release pollen at the same time; the endosperm develops from genes from both parents, and heterozygous kernels will be tough and starchy. The se and su alleles do not need to be isolated from each other. However supersweet varieties containing the sh2 allele must be grown in isolation from other varieties to avoid cross-pollination and resulting starchiness, either in space (various sources quote minimum quarantine distances from 100 to 400 feet or 30 to 120 m) or in time (i.e., the supersweet corn does not pollinate at the same time as other corn in nearby fields).
Modern breeding methods have also introduced varieties incorporating multiple gene types:
- sy (for synergistic) adds the sh2 gene to some kernels (usually 25%) on the same cob as a se base (either homozygous or heterozygous)
- augmented sh2 adds the se and su gene to a sh2 parent
Often seed producers of the sy and augmented sh2 types will use brand names or trademarks to distinguish these varieties instead of mentioning the genetics behind them. Generally these brands or trademarks will offer a choice of white, bi-color and yellow varieties which otherwise have very similar characteristics.
Bt corn is genetically modified to resist certain insects. Commercial growers have access to sweet corn seed bred with this artificial trait. Bt corn and other transgenic varieties are not available to the home grower due to protocols that must be followed in their production.
- Erwin, A. T. (July 1951). "Sweet Corn—Mutant or historic species?". Economic Botany (Springer New York) 5 (3): 302. doi:10.1007/bf02985153.
- Schultheis, Jonathan R. "Sweet Corn Production." North Carolina Cooperative Extension Service, North Carolina State University. Revised 12/94.
- "Stewart's Wilt of Corn". Retrieved 2014-07-07.
- Levey Larson, Debra (August 2003). "Supersweet sweet corn: 50 years in the making". Inside Illinois (University of Illinois at Urbana-Champaign) 23 (3). Retrieved 2009-09-03.
- Mann, Charles Kellogg. 1491: New Revelations of the Americas Before Columbus. Vintage. p. 221. ISBN 1-4000-3205-9.
- "Cooking sweet corn boosts its ability to fight cancer and heart disease by freeing healthful compounds, Cornell scientists find". Cornell News. Retrieved 2009-09-07.