Methods and Benefits of Cereal Milling: Wet vs. Dry Processing

Milling of cereals is an ancient art that dates back thousands of years, with evidence suggesting that it was practiced as early as 6000 BCE. The primary objective of milling is to make cereals more palatable and digestible, while also removing inedible or less desirable components, such as bran fractions, which consist of the outer layers of the grain. These bran fractions are often removed to produce finer, smoother flours that are easier to cook and consume, though in some cases, such as whole grain products, they are left in for added nutritional benefits like fiber, vitamins, and minerals.

Corn flour, a key product derived from cereal milling, can be produced through two main methods: wet milling and dry milling. Wet milling is a more intricate process that starts by thoroughly cleaning the corn to remove broken kernels, chaff, and other impurities. Once cleaned, the corn is steeped in warm water for an extended period, which softens the kernel and facilitates separation. This steeping process breaks down the corn’s cellular structure, making it easier to isolate the desired starch and germ from the bran. The resulting slurry, a mixture of softened corn and water, is then processed in a degerminating mill, which removes the germ (rich in oils) and produces a fine flour.

On the other hand, dry milling is a simpler, less time-consuming method. After the corn is cleaned, it is passed through a steaming conveyor. The steam toughens the hull, making it more brittle and easier to remove during the grinding process. This method yields a coarser product but retains more of the kernel's nutrients. Unlike wet milling, which focuses on starch production, dry milling is typically used when the goal is to produce cornmeal or other coarse flours for culinary applications.

Both methods are valuable, with wet milling commonly used for large-scale industrial purposes, and dry milling suited for traditional food products.
Methods and Benefits of Cereal Milling: Wet vs. Dry Processing

Oats processing: Cleaning

Mill processing starts with the arrival of oats from the farm or storage facility. The miller only accepts oats that will yield flakes of satisfactory quality and will attempt to maximize profits by estimating the potential yield.

Oats arrive at the mill via bulk railcar or truck and are sampled to ensure suitable quality for milling. Once the grain is deemed acceptable, the oats enter the mill, they pass under a magnetic separator to remove foreign metal objects.

The oats are then cleaned, mainly on the basis of physical properties of the grain. Sieves are used to remove contaminants on the basis of size.

The cleaning process utilizes several devices to take advantage of particular physical properties of the grain.

The oats experience a series of rotating or oscillating screens that can both retain large objects (such as straw, sticks and stone) and let small objects such as underdeveloped oats, dirt, weed seeds and dust to pass through. The retained oat stream is then subjected to aspiration to remove more of the light materials.

This is followed by a dry stoner that removes high-density but similar-sized particles such as rocks and other grains, such as maize.
Oats processing: Cleaning

Wheat milling in ancient history

It is generally believed that wheat had its origins in the regions of the ancient Eastern region of Egypt, Mesopotamia and the Levant, around 7000 B.C, although it had likely been gathered as a wild grain much earlier.

The grain was placed in a large saucer-shaped stone, a smaller rounded stone was used to crush it. Saddle querns seem to be the most common cereal grinding tools through all prehistory and early history of Mesopotamia and the Mediterranean.

The process of milling wheat into flour was revolutionized around 800 BC in Mesopotamia, when animal, water and wind power were harnessed for the first time to run the large stones used for grinding.

These mills were often constructed using good quality stones, the grinding process could have been repeated several times and finally flour was sieved.

In ancient Rome the mill and the bakery were the very same enterprise. The grains were milled and worked up without delay to dough and bread.

In the Middle Ages the milling of four became the monopoly of a few professional millers who were granted this concession by the wealthy landholders who built the large mills.

The first wind-powered mills were built in England in the 11th century, and in Belgium Luxemburg and the Netherlands in the 12th century.
Wheat milling in ancient history

Wheat processing: Milling

The single term ‘milling’ applied in the context of cereals, covers a wide range of processes. Wheat is milled in a continuous process to remove the bran and germ and reduce the wheat kernel to flour to be used in various baked and nonbaked goods.

A small portion of production is geared towards the production of whole-wheat flours employing a simplified process flow sheet, but most demand and effort is directed towards the production of white flour. The conventional milling process of wheat first involves washing to remove foreign substance such as dirt or rocks.

Milling is a process by which kernel components are separated physically or chemically. Once the endosperm is separated it subsequently is ground multiple times in reduction rolls to become finer and finer for flour.

As the bran and germ are removed, the refined flour contains streams that contain less vitamins and minerals. If flours streams of the endosperm are blended during the milling process various flours are created. Other products of the process, e.g. vital gluten, can supplement other edible products.

Millfeeds, the material remaining after all the usable flour is extracted is used by the feed industry either directly or as a feed supplement.

Wheat milling practices might cause significant differences in flour quality, which are due to flour particle size, extraction rate, and the level of starch damage.

In general, 100 pounds of wheat will produce 72 pounds of flour. The remaining 28 pounds is classified as millfeed.
Wheat processing: Milling

The Wet Milling of Corn

The corn wet milling process was developed in the early 19th century at which time alkali was used. This wet milling is a complex used for manufacturing of corn starch and the various sweeteners obtained from its hydrolysis.

The development of wet milling was based on the observation that a white, insoluble granular material settled to the bottom of the pan when quantities of cut tubers were washed.

As opposed to dry milling, which separates the anatomical parts of the corn kernel, wet milling separates the kernel components into their chemical constituents.

In the corn wet milling process, the use of SO2 is very important. It breaks down the protein matrix that surrounds the starch particles and increases starch yield during milling.

The wet milling process consist of cleaning the grain, an initial soaking in water to soften the kernels, milling to separate the components through screening, centrifuging and washing and finally, production of the end products: starches, sweeteners, proteins and co-products.

An enzymatic corn wet milling then has been developed that’s shows the potential to reduce or completely eliminate the use of SO2 and produce starch yields comparable to the conventional corn wet milling.

Wet milling creates a high-quality cornstarch slurry used in the production of syrup as well as in the manufacture of high quality dry starch.
The Wet Milling of Corn

Grain Processing: Milling

Milling is a series of operations involving the grinding of grains to produce starch or flour, most commonly from wheat, oats, corn, rye, barley or rice.

Threshing removes the grain from the stem. However, the grain is not usually ready for cooking until the husk (glumes) has been removed.

The exact details of grain processing depend on two main factors; the physical structure of the grain concerned and the nature of the flour product being made from that given grain.

Wheat, sorghum and pearl millet usually thresh naked that is without the glumes. Maize is on a cob covered with a sheath: the sheath must be removed and the grain taken from the cob.

A combine harvester threshes the maize free from both sheath and cob. Barley, oats, rice and most of the small millets thresh with the glumes adhering tightly to the kernel so that even a modern threshing machine or a combine harvester cannot remove the grain from this husk.

The first step in any milling process for this latter group is to remove the glummer. This is done by rubbing the grains one against the other in a mortar or by simple rotary machine, by splitting off the glumes in a disk huller, or by use of rubber rollers rotating at a differential speed.

The objective at this stage of milling is to obtain as high an out-turn as possible of whole grains.

Once free from glumes, all grains may be treated in the same way. Cereals have an outer layer and a gem, known collectively as bran, which is rich in lipids that rapidly oxidize to give off-flavors. The bran also tends to be less easily digested than the endosperm.

Milling of wheat into flour has two principle aims: to separate the bran from the endosperm; and to reduce the endosperm particles to assize sufficiently small to be rapidly hydrated on subsequent processing.

The objective of the second stage of milling is, therefore, to remove the bran. In the case of rice, the grain is required whole, so great care is taken not to break the grain.

In the process of rice polishing, separation of bran from endosperm is achieved simply by abrading the outer bran layers away leaving the intact endosperm.

Most other cereals are eaten as flour or meal (a coarse flour). The more of the bran that is removed, the better the flour will keep.

Grain Processing: Milling

Wheat cleaning and milling

Before the wheat reaches the milling stage, first it has undergo several preliminary operations that ensure the correct of the main process. The first of these is wheat cleaning.

Wheat is passed through a series of machines that apply the principles of particle size and density separation.

Foreign materials such as metal, sticks, stones, straw, seeds and other grain are removed in steps by a magnetic separator, vibrating screens, a destoner, a disc separator and a scourer.

Sieves remove contaminants larger than wheat kernels as well as finer contaminants such as sand. In addition, air is used to remove plant material that is lighter than the grain.

After cleaning, the wheat is tempered prior to be milled. In this stage, the moisture content of the grain is increased by adding water and by allowing the grain to sit for a period of time.

Wheat is milled to remove the bran and germ and reduce the wheat kernel to flour to be used in various baked and nonbaked goods.

In general, 100 pounds of wheat will produce 72 pounds of flour. The aimed of white flour milling is to extract a maximum amount do endosperm from the wheat berry in as pure a form as possible.

The wheat is passed through a series of machines to break open the wheat kernels and reducing of the endosperm by grinding to obtain the final product – plain flour.

Additives of less than 1 weight % are added to the flour by a mixing process.

Family four for retail sale is packed in 5, 10, or 25 pound bags. Bakery flour may be packed in 50 or 100 pound bags or shipped in bulk trucks or railcars.

Wheat cleaning and milling