Sweet corn (Zea mays convar. saccharata var. rugosa) is a grouping of maize known for high sugar content. 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.
The Iroquois Indians gave the first recorded sweet corn (called Papoon) to European settlers in 1779. Open-pollinated varieties of white sweet corn started to become widely available in the United States in the 19th century. Two of those varieties – still available today as “Heirlooms” – are Country Gentleman and Stowell's Evergreen.
Sweet corn production in the 20th century was influenced by the following key developments:
1. Hybridization allowed for more uniform maturity, improved quality and disease resistance.
2. Identification of the separate genes responsible for sweetness in corn and the ability to breed varieties based on these characteristics:
• su (normal sugary) – su varieties are best when cooked within 30 minutes of harvest.
• se (sugary-enhanced; originally called Everlasting Heritage) – se varieties have a longer storage life and contain 12 to 20% sugar compared to su varieties.
• sh2 (“supersweet” shrunken-2) – sh2 varieties’ kernels store less starch and from 4 to 10 times more sugar than su varieties.
3. There are currently hundreds of varieties of corn, with more constantly being developed. The se and su varieties do not need to be isolated from each other. However sh2 supersweet varieties must be grown in isolation from other varieties to avoid cross-pollination and resulting starchiness.
Despite their short storage life, many O.P. (open-pollinated) varieties such as Golden Bantam still remain popular for home gardeners – often marketed as heirloom seeds. Although less sweet, they are often described as more tender and more flavorful than many hybrid varieties.
Modern breeding methods have also introduced varieties incorporating multiple gene types. They are normally marketed with brand names and/or trademarks by seed producers, and offered as a choice of white, bi-color and yellow varieties which otherwise have very similar traits.