Corn is a cereal crop used in food and animal feed. Wet milling extracts germ, fiber, starch, and gluten for various products. Dry milling ferments corn into ethanol for fuel and produces by-products for animal feed.
Maize, also known as maize in many countries, is an important cereal crop produced around the world for use in a wide variety of foods and as livestock fodder. After being harvested, corn must undergo milling to be refined into products. The two main corn milling processes are wet milling and dry milling. Wet milling is used to make food ingredients and animal feed, while dry milling is mainly used to make ethanol, a widely used alcoholic compound that has applications as a biofuel.
A single grain of corn consists of several useful components. The germ, or embryo of the plant, contains oil. The fleshy part of the kernel that surrounds the germ, called the endosperm, contains starch; a carbohydrate or sugar; and gluten, a protein. In industrial corn milling, the goal is to extract these components from the kernel so they can be used to create various products.
Wet milling of corn begins with dry corn cobs, which are soaked in tanks of water with lactic acid and sulfur dioxide to soften the kernels and dissolve the starch. After this step, the corn is ground. The germ is removed by passing the ground corn and water through a separator, which causes the oily germ to float to the surface. This part of the kernel can be used to make corn oil; foodstuffs; and germ meal, a livestock feed.
After the germ has been removed, the fiber, also used in animal feed, is separated from the remaining starch and gluten. Centrifuges spin the starch and gluten at high speeds, causing them to separate by density. Gluten is added to fiber for use in animal feed, and starch is used in human food, textiles, paper, and many other applications. Starch makes up the majority of products obtained from wet milling of corn, followed by gluten and corn oil.
Dry milling corn involves fermentation, a biochemical process in which ethanol is produced from the sugars in the corn kernels. In the first stage of this process, the corn is ground into a fine flour. The starch in this meal must then undergo liquefaction. Water and an enzyme are added to aid in a hydrolysis reaction, which breaks down starch molecules into long sugar chains.
Next, the starch is heated to destroy unwanted bacteria and broken down into more basic sugars using another enzyme. Yeast is added to metabolize sugar. Through the metabolic activity of the yeast, the sugar is converted into ethanol and carbon dioxide. This process is known as fermentation. The main product of dry milling, ethanol, has a multitude of uses as a chemical and industrial fuel, while the by-products of the process can be used as further additions to animal feed.
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