Raw oats used by the oat milling industry undergo initial processes of cleaning and hulling. Cleaning removes the unwanted materials – such as corn, soybeans, foreign material, weed seeds, wheat, or barley. – from the milling quality oats. Various screening machinery, making size separation by length and width, remove these unwanted materials and also size the oats. With the use of air, called aspiration, loose hulls and lighter feed grade oats are also removed.
The next step is the hulling process, where the outer shell (hull) is removed from the inner kernel, called the groat. The hull is removed by large machines that fling the oats against a rubber ring, knocking the hull off without damaging the groat.
These groats are then further processed to make an edible food product from a raw grain. The mixture of groats and loose hulls flow into another set of aspirators, where the much lighter hulls are blown off. The groats enter scouring machines where brushes clean the groats.
In the conditioning process, moisture content is increased before the groats pass through a kiln where they are heated using dry heat radiators to a temperature of approximately 215 degrees F. During the heating process, steam inactivates enzymes present in raw grain, the groats are given a roasted nutty flavor, starch gelatinization occurs, and moisture level is reduced to a point acceptable for product storage. Adjustments are made to the conditioning system depending on the desired finished product characteristics.
Product then enters the sizing system where width graders are used to size the individual pieces. Large groats enter the groat stream, while small groats and broken pieces are sent to the cutting system. In the cutting system, steelcut is produced from the groats and broken pieces. A small sifter is used to segregate the large and small pieces of steelcut. Small pieces are often referred to as baby steelcut (baby flakes are produced from it), while the mixture is referred to as regular steelcut. The large pieces are called large steelcut.
The flaking system uses steelcut or groats as raw material and produces flakes. Before flaking, the products must be steamed to increase the moisture and elasticity. Large steelcut passes through the flaking mill to produce quick (minute oats, three minute) and thick quick, while baby steelcut produces baby flakes. Whole oat groats are rolled into various old fashioned type flakes.
Following rolling, the flakes are dried to approximately 11% moisture on a bed dryer before being packaged.
The flour and bran system produces whole oat flour, or a combination of low bran oat flour and oat bran. Rollstands and hammermills are used to grind the product into flour or bran. Various granulations of both flour and bran can be produced.
Crushed oat products are produced using an attrition mill. Steelcut, groats, or flakes can be milled into crushed oat products. Granulation requirements determine which product to mill, and how to set the mill.