Types of Corn

Study Notes

Corn, Zea Mays, thrives in warmer climates and is cultivated worldwide.
Dent Corn: Possessing both hard and soft starch, it becomes indented upon maturation. Used for producing food, animal feed, and industrial products.
Flint Corn: Contains hard, horny kernels with a soft and starchy endosperm. It is similar to Dent Corn and has the same applications. Mainly grown in South America.
Waxy Corn: Contains solely branched-chain starch, resulting in grains with a waxy appearance when cut. Used to make special starches for thickening foods.
Sweet Corn: A specific mutation of Dent Corn, it has high sugar content during the Milk Stage which makes it ideal for table consumption.
Indian Corn: Features kernels in various colors including white, red, purple, brown, and multi-colored. It was the original corn cultivated by Native Americans.
Pop Corn: Characterized by small ears with rounded kernels. When exposed to dry heat, the contained moisture expands, and the kernel explodes to form a starchy mass.
Flour Corn: Primarily composed of soft starch. Small quantities are grown in the USA for making tortillas, chips, and baked goods.

Dry Milling: The separation of the maize kernel into its constituent parts.
Wet Milling: Another method for separating the maize kernel into its components. Both processes yield corn oil, which is extracted from the germ, and the hull is removed, leaving behind the high fiber portion.
Dry Milling Process:
- Cleaning: Removal of dust, foreign bodies through dry and wet methods, including sieving, particle separation by shape/density, and removing magnetic materials with magnets.
- Conditioning: Adding water to the kernel to achieve a desired moisture content (typically 21%).
- Degermination: Separation of the hull, tip cap, and germ, leaving the endosperm as larger grits.
- Drying: Reducing moisture to 15-18% for proper grinding and sifting. Performed using rotary steam tube dryers.
- Cooling: Dried products are cooled with counter-flow or cross-flow rotary coolers.
- Grading: Sifting and classification based on particle size, resulting in the separation of bran and germ while maximizing the amount of clean large grits.
- Milling: Involves grinding, sifting, classifying, purifying, aspirating, and in some cases, final drying. Typically uses break rolls, followed by reduction rolls to grind the endosperm to the desired particle size.

Cleaning: Removal of dust and foreign objects from shelled corn.
Steeping: Soaking corn in water (called steepwater) at 50°C for 20-30 hours, resulting in a doubling of the corn's size. Sulfur dioxide is often added to inhibit bacterial growth and preserve starch quality.
Degermination: The softened corn is ground in a wet state, separating the germ from the endosperm.
Separation: The resulting slurry is then further separated into its constituent parts – fiber, starch, and gluten – through a series of operations including hydro cyclones and centrifugation.
Oil Extraction: The germ is dried and pressed for oil extraction.
Ethanol Production: Some of the starch is processed into ethanol.
Animal Feed: Residues from the wet milling process are used as animal feed.
Corn Steep Liquor: The water from the steeping process (steepwater) is concentrated and dried, producing corn steep liquor which is used as a source of growth factors in animal feed.
Evaporation: Water is evaporated from the starch slurry, resulting in corn gluten meal.