The sugar content of sweet corn is measured with a refractometer. The amount of sugar in sweet corn depends on the type of corn, the variety, the maturity at the time of harvest and the post harvest handling. Three general types of sweet corn are recognized. Normal sugary (su) corn contains the sugary1 gene mutation. Sugar enhanced (se) corn contains the sugary enhancer1 gene mutation, in addition to sugary1. Supersweet (sh2) corn contains the shrunken2 gene variation. Newer varieties may have a combination of all three genes. Brix readings range from 10% to 15% for su corn, 13% to 28% for se corn, and 25% to 35% for sh2 corn. Sugars are converted to starch as the corn matures and after harvest. In sh2 corn, this conversion is much reduced, leading to greater retention of sugar content after harvest.

The texture of the sweet corn also depends on the type of corn, the variety, and the maturity at the time of harvest. Sweet corn kernels contain phytoglycogen, which provides the characteristic creamy texture. The covering or pericarp of the kernel contributes to the sense of texture. The pericarp of su and se corn is similar, while the pericarp of sh2 corn may have a crunchy texture or firmness, depending on variety. Within each sweet corn type there is a range of firmness associated with the pericarp; se corn tends to have a more tender pericarp than su corn. Kernel size and number creates a visual texture. Early-maturing varieties with fewer rows (12 to 14 rows per ear) and large kernels appear coarse textured compared to the more refined look of a mid-season or main season 18-row corn with smaller kernels.

Sweet corn is seldom harvested or sold based on brix readings, but rather by percent moisture or for fresh market, by the way the ear feels when grasped. Fresh market corn is normally harvested when less mature than corn for processing. The percent moisture for su or se corn for processing will be in the range of 72% to74% moisture while fresh market corn will be 75% to77% moisture. Shrunken2 corn can be as high as 78% moisture for fresh market.

Supersweet corn must be grown in isolation from either su or se corn or field corn. Pollen from any other corn type will cause sh2 corn to be starchy. A distance of 250-300 feet will generally prevent cross pollination. If distance can not be provided planting days can be planned to insure at least 14 days separation between tasseling and silking dates of the different varieties. Similarly, su and se corn must be isolated from field corn and from sh2 corn to prevent cross-pollination and development of starchy kernels.

Sweet corn harvested too early will have a watery taste and the kernels will resemble blisters. The sugar level will not be high enough. Sweet corn harvested past optimum maturity will be starchy and the kernels will be more like dough instead of milky or creamy. Sh2 corn has a wider window of time during which the crop may be harvested with good quality.

Sweet corn has a high respiration rate at warm temperatures causing rapid conversion of sugar to starch, and loss of sugars to oxidation. The field heat must be removed as soon as possible to avoid loss of quality. Hydro-cooling or slush ice injection are excellent choices for cooling.

All types of sweet corn are available in yellow, white and bicolor. A few specialty varieties with partly red or all red kernels are available. The various varieties come in different shades. White corn for example comes in bright white to a cream or ivory. The kernels may appear dull or bright.

Cross pollination of yellow varieties with white or bicolor varieties will cause yellow kernels in the white variety and a reduction in the number of white kernels in the bicolor. Pollen from white varieties will have no effect on yellow or bicolor varieties.

An ear with dark green husk color and medium size flag leaves presents an attractive package to the consumer

The size of ear is small for early varieties and increases with later maturing varieties. The length ranges from 6 inches to 10 inches. The ear diameter varies from 1.5 inches to 2.00 inches. Ears that are 10 inches long with a 2-inch diameter are difficult to pack in bags and crates in the customary 5 dozen count.

Ear size will be reduced by any condition placing stress on the plant including poor nutrition, drought, excess moisture, weeds, cold temperatures, compacted soils or plant populations that are too high. The plant population should be about 22,000 plants per acre. Recommendations for spacing and cultural practices are available in the Midwest Vegetable Production Guide for Commercial Growers or through your local Cooperative Extension Service.

The bacterial disease Stewart's Wilt (Xanthomonas stewartii) and the virus Maize Dwarf Mosaic can debilitate the plant enough reduce the ear size and in severe cases kill the plant. Resistant varieties are becoming available in greater numbers with time.

Sweet corn is vulnerable to loss in quality from the environment, disease and insects. The grower is concerned about all of the problems involving growing the crop at a profit whereas the customer is concerned primarily with ear quality. A variety must have good eating quality, but aside from that the plant must perform well.

Stand Establishment in cold soils is an important consideration. Unless enough plants come up uniformly in early plantings the yield will be light and harvest may be inefficient. se corn has better cold soil emergence than sh2 and therefore is used for early plantings.

Stress on the plant can result in many defects. Varieties that have marginal tip cover will have exposed tips. The exposed tips then result in more bird damage. Dry and hot weather during silk can result in poor tip fill. Some varieties that are excellent in most other characteristics may have a lodging problem when the wind blows. Hand harvest crews are very much aware if a variety picks hard. Stress will cause a plant that normally has good flag leaves to have poor flags.

Smut Rust European Corn Borer, Corn Earowrm, and Fall Armyworm

Shelf life is dependent on harvesting the sweet corn at the optimum maturity and reducing temperature immediately down to 32˚F to 34˚F. Sweet corn should be kept at this temperature during transit and any storage that is necessary incident to sale. Sweet corn storage time is 5 to 8 days. Icing or slush icing is recommended. The relative humidity in storage should be 95% 98%.

Serving Size: 1 medium ear of corn (90g)
Amount Per Serving	% Daily Value*
Calories 80 Calories from Fat 10
Total Fat 1g	2%
___Saturated Fat 0g	0%
___Cholesterol 0mg	0%
Sodium 0mg	0%
Total Carbohydrate 18g	6%
___Dietary Fiber 3g	12%
___Sugars 5g
Protein 3g
Vitamin A	2%
Vitamin C	10%
Calcium	0%
Iron	2%
*Percent Daily Values are based on a 2,000 calorie diet.
(Source: Produce Marketing Association's Labeling Facts, February 1994.)