Shelled corn enters the system through cleaning machines,which remove foreign material. Cleaned corn then goes to a steep tank holding up to 25,000 bushels, where it soaks in circulating water, maintained at 125 and slightly acidified with 0.1 to 0.2 percent of sulfur dioxide. Steeping the corn for 24 to 48 hours softens the kernel, loosens the hull and germ and swells the endosperm. Steeping takes place in a series of tanks, which are operated in a continuous batch process.
The water circulates counter currently through the tanks, so when it is finally with drawn from the newest batch, it has a relatively high concentration of soluble. The steeping process facilitates separation of the components of the kernel and loosens the gluten bonds to release the starch. Discharged steep water, rich in protein at 35 to 45 percent of total solids, is concentrated in vacuum evaporators to a solids content of 35 to 55 percent. Steep water concentrate is utilized in feed products or in industrial fermentation media.
Softened corn from the steep tanks is coarsely ground with water in an attrition mill to free the hull, the germ and a large portion of the floury endosperm starch and gluten. The slurry of coarsely ground corn is forced under pressure into hydro cyclone, which centrifugally separate the lighter corn germ, which is then carried off to washing screens. Washed germ is conveyed to a dryer and from there to oil recovery facilities. Washings from the germ are piped to the starch centrifuges. Heavy fractions from the coarse grinding mills and germ separators are passed through fine grinding mills and washing screens for fiber separation. Finally, the slurry is sent to centrifuges for separation of gluten (light phase) from starch (heavy phase).
The gluten fraction passes to a centrifugal concentrator and is filtered and dried. The starch stream goes to washing cyclones fed with fresh water; overflow, containing residual gluten from the ¡°mill starch, is recycled to the starch centrifuge; underflow from the washing cyclones, a suspension of starch containing only about 0.3 percent protein, is passed through a concentrator and dryer, from which the finished starch product emerges.
