Corn wet-milling facts for kids
Corn wet-milling is a special way to take apart corn kernels. It separates them into different useful pieces. These pieces include corn oil, protein, corn starch, and fiber. This process uses water and several steps to get each part ready for many products.
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How Corn Wet-Milling Began
The corn wet-milling industry has been a big part of American making things for over 150 years. Companies learned how to separate corn kernels into their parts. This helped them make many valuable products. The main parts are oil, protein, starch, and fiber. These are the first products from corn wet-milling. In 1913, the corn refining companies grew a lot. They then formed a group called the Associated Manufacturers of Products from Corn.
What is Corn Wet-Milling?
Corn wet-milling is a process that takes out parts from corn kernels. It makes very pure products. Most of these products are valuable. The food industry uses them a lot. Every part of the corn is useful in this process. It helps make high-quality ingredients.
This process separates things mostly by their weight and size. Water is very important because it's a "wet" process. Water helps separate and carry the parts during washing. This process can cost a lot of money to set up. The only chemical used is a watery sulfur dioxide solution. This is used in the steeping process. Corn soaks in this solution. This softens the kernel. It also helps separate the oil from the germ. This stops the oil from mixing with other products.
Steps in the Process
Cleaning the Corn
The U.S. Department of Agriculture usually uses Grade 5 corn for wet-milling. First, harvested corn must be cleaned before it is milled. A special machine removes things that are not corn. These can be pieces of cob, other seeds, metal, leaves, or dirt. After cleaning, the corn is checked for what it contains. This is done using a special machine called an NIR spectrometer.
Steeping the Corn
In this step, corn soaks in water. This makes the starch granules loose from the protein. It also keeps the germ strong for milling. Soaking makes the germ lighter and softens the kernel. This makes milling easier. Chemicals like sulphur dioxide and lactic acid are added to the water. Lactic acid breaks down the protein in the endosperm. This helps starch separate better. It also lowers the pH, which stops tiny germs from growing. Sulphur dioxide helps weaken the bonds that hold the starch. This lets starch granules separate cleanly. It also stops germs from growing.
After soaking, the protein is weaker. Some parts of the endosperm dissolve into the steepwater. Clean corn soaks in big tanks. The water is warm (about 125-130˚F). It contains lactic acid and sulphur dioxide. This soaking lasts for about 40 hours. Then, the steepwater is drained using screens. It is then made stronger using special machines. This strong steepwater has a lot of protein. It can be used to grow enzymes or antibodies. It is also used in animal feed.
Getting the Germ Out
This step separates the germ from other corn parts. It is important to keep the germ whole. This stops oil from getting into the final products. Special mills, like disk mills, grind the softened corn kernels. The grinding is slow. The grinding parts are blunt. This makes sure the germ comes out whole. Water is added to the ground corn. This makes a thick liquid with crushed kernels and whole germ. The germ has 40-50% crude oil. This makes it lighter than other parts. So, the germ floats in the mixture.
The mixture then goes through germ hydrocyclones. These machines separate things by spinning them. The top part will have mostly germ and water. The bottom part will have fiber, starch, protein, and water. The top part goes through the hydrocyclone many times. This is because it's hard to separate everything in one try. The separated germ is cleaned and dried. Then, it goes through a germ press to get the oil out. Another way to get oil is using chemicals. The solid parts left after getting the oil out are called germ meal. This is dried further.
Germ meal has many amino acids. It is used in animal food. The refined corn oil can be used for salads and cooking. It also helps make corn oil margarines.
Getting the Fiber Out
The liquid from the hydrocyclone has fiber, protein, and starch. This is ground very finely. Then, it is screened using many grind mills and screens. Screens are used to separate the fiber from the mixture. Different screen sizes remove coarse and fine fibers. Starch and protein pass through the screen and are collected. The fibers stay on the screen. This is called corn gluten feed. Separation happens because of different sizes. Corn gluten feed has about 21% protein, 1% fat, 10% fiber, and 15% starch. It has many water-soluble nutrients. So, it is a main ingredient in animal feed. It can also be used to make refined corn fiber for people to eat.
Getting the Protein Out
The liquid with only protein and starch is called millstarch. Water is taken out of the millstarch. Then, it goes into a separator. Spinning forces separate the starch and gluten. They have different weights. The heavier starch liquid is washed many times. This is done in hydrocyclones with fresh water. The starch stream usually has 90% starch. The gluten stream has 60% protein. The lighter gluten separates from the top. It is made thicker. The heavy gluten is sent for dewatering into a vacuum rotary filter. This corn gluten meal has about 60% protein, 1% fat, and 3% fiber. Water from both processes is either added back to the steepwater or removed. Since it has about 60% protein, it is used as animal feed and for zein products.
Processing the Starch
Starch goes through many washing steps. This is done using hydrocyclones. The liquids from each washing step are separated. The water from each step is used again in earlier hydrocyclones. This makes sure almost all the starch is separated. Very pure starch (over 99.5%) can be recovered by wet-milling. Purity is important if the final product is high-fructose corn syrup. It is also important if the starch will be changed using chemicals or enzymes. But purity is not as important when making ethanol fuel. After spinning and washing, the starch is dried.
Other Products Made
Other products, called co-products, make up 34% of what comes from wet-milling. The fiber, strong steepwater, and germ meal are mixed. This makes corn gluten feed. As mentioned, corn gluten meal is also used for animal feed. Even though both have 'gluten' in their name, corn does not have gluten protein.
Main Products
The wet-milling process makes five main products. These are steep water solids, germ, fiber, starch, and gluten. But the co-products from this process make corn oil, corn gluten meal, corn germ meal, corn gluten, and feed steep water. On average, one bushel of corn usually gives about 32 pounds of starch. Or it can give 33 pounds of sweeteners. Or 2.5 gallons of fuel ethanol. It also gives 11.4 pounds of gluten feed, 3 pounds of gluten meal, and 1.6 pounds of corn oil.
New Ideas in Corn Wet-Milling
People have used corn wet-milling for many years. It makes food, animal feed, and fuel. But researchers are still looking for better ways to do it. For example, one study showed that soaking time can be much shorter. It can go from 40 hours to 6–8 hours. This happens if enzymes like protease are added. Also, if the milling is done in two steps. This method does not need sulphur dioxide. It still makes the same amount of product as the old way. Another study showed that adding other enzymes also shortens soaking time. In the usual process, a substance called phytic acid ends up in the steep liquor. Another study tried to use less water at the start. They also tried to use hotter drying air. But this led to less product. This was because low water made it hard to separate protein from starch.
