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Wet mill is both a cereal grain production process and the machinery used for wet milling. The wet milling process involves using water to break down grains prior to milling. This allows the individual parts of the grain to separate from one another for easier harvesting. The wet mill process is a common method of harvesting grain for food components, but dry milling is more common for flour or ethanol production.
It is common to use a wet mill on a variety of different feed materials commonly called cereal grains. The basic idea is that the material softens and breaks down in the water. When the feed material is milled, it will take less energy to pulverize it since it is already soft, and it will break down into its constituent pieces more easily.
The first step in a wet mill procedure is steeping the material to turn it into slurry. The food is placed in a tank filled with warm water and allowed to sit for one to two days. While in the water, the food softens as its internal protein bonds begin to break down. This water generally has a small amount of sulfur dioxide mixed in. This prevents the warm and mushy food from growing harmful bacteria. After the slurry leaves the tank, the starch-rich water is purified and condensed for use in animal food or fermentation.
The slurry is very coarsely ground to finish its basic dissolution. This results in a warm and wet mash that is near uniform in consistency. During this stage, any germ that is still attached to the food product is broken apart. In a grain, the germ is the part of the seed that would actually grow into another plant. This portion of the grain is used to create the majority of vegetable oils.
The next step in the wet mill process is the separation of the germ from the rest of the slurry. The slurry is placed into cyclone tanks and spun. The germ’s lower density allows it to separate from the rest of the material so it may be pulled out of the mixture.
The slurry is now mainly made up of fiber, starch and gluten. The material is ground again, this time very thoroughly. After grinding, the mixture moves over a series of screens, separating the fiber from the rest. This fiber is screened several more times to assure its relative purity, and then it is made into animal feed.
The gluten and starch enter a centrifuge, where the lower density gluten comes apart from the starch. The gluten is turned into several products, both for humans and animals. The starch is converted into products like cornstarch or processed into corn syrup and dextrose.