Know your Sweet Corn

  • Sweet corn (Zea mays convar. saccharata var. rugosa; also called Indian corn, sugar corn, and pole corn) is a variety of maize with a high sugar content and it is prepared for consumption as a vegetable.

Know your Sweet Corn - Botany

  • Sweet corn, Zea mays, is a monocot in the grass family, Gramineae
  • Modern sweet corn cultivars arose in the 19th century when a single gene (su) mutated in field corn. 
  • Plants descended from this mutant had kernels with a sugary rather than a starchy endosperm and a creamy texture. 
  • The low starch levels make the kernel wrinkled rather than plump. 
  • Sweet corn also has a thinner pericarp (seed coat) than field corn, making it more tender. 
  • Corn is monoecious, which means that there are both male and female flowers on each corn plant. 
  • In some monoecious plants, male and female parts are in the same flower. 
  • In corn, male and female flowers are in different locations - the male flowers form a tassel which is at the top of the plant. 
  • The female flower is located at the junction of leaves and stem. 
  • It consists of a collection of hairs (silks) enclosed in the husks of what will become the ears. 
  • These silks are pollen-receiving tubes. 
  • Wind-blown pollen from the male flowers (tassel) falls on the silks below. 
  • Each silk leads to a kernel, and pollen must land on all silks for the ear to fill out completely with kernels. 
  • Kernel "skips" (ears only partly filled out with kernels) often are the result of poor pollination.

Know your Sweet Corn - Origin

  • Field corn traces its lineage to ancient types such as pod corn, which was grown in Mexico in prehistoric times. 
  • In pod corn, each kernel is enclosed in its own husk. 
  • Many colourful and flavourful types of corn are still grown in the southwestern United States and in Central and South America. 
  • Collectively these types are sometimes referred to as 'Indian corn' and are grown in the United States for the decorative ears.
  • Within the last 20 years, sweet corn breeders in the USA have introduced new genes which further increase kernel sugar content and extend shelf life. 

Know your Sweet Corn - Culinary Uses

  • 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 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 fresh, canned, or frozen before the kernels become tough and starchy.

Know your Sweet Corn - Varieties

  • Sweet corn may be divided into three distinct types according to it's genetic background:

Standard sweet corn

  • Seeds germinate early
  • Seedlings have good vigour
  • Cobs are fairly sweet, but the sugar they contain quickly turns to starch after picking.

Supersweet corn

  • Difficult to germinate as seeds are wizened, small and tend to rot in the soil.
  • This is the corn usually found fresh in supermarkets.
  • With 30% more sugar than standard they loose their sweetness more slowly.
  • Kernels can be chewy.
  • Grown closer than about 75m (246ft) to standard sweetcorn or livestock maize they cross-pollinate and loose their 'supersweetness'.

Extra tender, also called Triple Sweet

  • The latest cultivars, even sweeter than supersweet.
  • Meltingly tender kernels are ideal for growing on allotments.
  • Do not plant near ordinary or livestock maize because of cross-pollination.
  • Can be grown near supersweet cultivars.