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'Sweet corn' (''Zea mays'' var. ''rugosa''^[1]), also called 'sweetcorn', 'sugar corn', or simply 'corn', is a variety of corn 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 fully mature, sweet corn is picked when immature and eaten as a vegetable, rather than a grain. Since the process of maturation involves converting sugar into starch, sweet corn stores poorly and must be eaten, canned, or frozen before the kernels become tough and starchy.

Contents

History

Anatomy

Consumption

Varieties

Genetics

References

History

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.^[2] It soon became a popular vegetable in southern and central states.
Commercial production in the 20th century saw the rise of the ''se'' (''sugary enhanced'') mutants, which are more suitable for local fresh sales, and in the 1950s the ''sh2'' (''shrunken-2'') gene was isolated that minimized production of the enzyme that converts sugar to starch.^[3] There are currently hundreds of varieties, with more constantly being developed.

Anatomy

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''. The ear is covered by tightly wrapped leaves called the ''husk''. ''Silk'' is the name for the styles of 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''.

Consumption

The kernels are boiled or steamed, and usually served with butter and salt. In the UK, China, and Japan, they are sometimes used as a pizza topping. ''Corn on the cob'' is sweet corn cob that has been boiled, steamed, or grilled whole; the kernels are then bitten off the cob with the teeth or cut off the cob. ''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. See Corn nuts. A soup may also be made from the plant, called sweet corn soup.

Varieties

''Shoepeg corn'' is a particularly small, white variety of sweet corn. Kernels that are allowed to mature to hard grains are used as seed corn or ground into corn flour.
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. Some older varieties are best when cooked within 30 minutes of harvest [3]. 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.

Genetics

There are several different genetic mutations responsible for various types of sweet corn. Early varieties, such as those used by American Indians, were the result of the mutant ''su'' ("sugary") allele.^[4] They contain about 5-10% sugar by weight. Another form of the same gene, the ''se'' or "sugary enhanced" allele, was responsible for so-called "Everlasting Heritage" varieties, such as 'Silver Queen'. Varieties with the ''se'' alleles have a much longer storage life and contain 12-20% sugar.^[5] Beginning in the 1950s, plant breeders at the University of Illinois at Urbana-Champaign began developing 'supersweet' varieties, which occur due to a mutation at another gene (the ''sh'' or "shrunken" gene).^[6]
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 are on the same gene and do not need to isolated from each other. However, since ''sh2'' is a recessive allele on a different gene, supersweet varieties 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 / 30.5 to 122 m) or in time (i.e. the supersweet corn does not pollinate at the same time as other corn in nearby fields).
In colder areas, a fourth type of sweet corn, known as ''sy'' (for ''synergistic''), is often grown. This variety of corn mixes ''se'' and ''sh2'' kernels on the same cob and does not require isolation.

References

1. Sweet Corn
2. "Sweet Corn Production." Jonathan R. Schultheis, North Carolina Cooperative Extension Service,
North Carolina State University. Revised 12/94. [1]
3. [2]"Supersweet sweet corn: 50 years in the making." Debra Levey Larson. ''Inside Illinois'' Vol. 23, No. 3, Aug. 7, 2003. University of Illinois at Urbana-Champaign news bureau.
4. "Sweet Corn Production." Jonathan R. Schultheis, North Carolina Cooperative Extension Service,
North Carolina State University. Revised 12/94. [4]
5. "Sweet Corn." Oregon State University Horticulture 233 webpage. [5]
6. [6]"Supersweet sweet corn: 50 years in the making." Debra Levey Larson. ''Inside Illinois'' Vol. 23, No. 3, Aug. 7, 2003. University of Illinois at Urbana-Champaign news bureau.