Bioethanol, alcohol for drinking and technical-grade alcohol can also be obtained from raw materials containing starch with the aid of the dry process which, although an established process, does not allow protein to be obtained separately as in wet milling.
In the dry-milling process, the whole grain is milled and mashed with water, with the starch being gelatinized by the addition of steam. This is a necessary step for enzymatic splitting of the starch molecules. The pH-value is adjusted and enzymes are added to bring about saccharification. This sugar syrup is then fermented with yeast to form alcohol. The fermentation broth passes through a distillation column in which raw alcohol is distilled off and then further processed to produce ethanol.
What is left behind also has value. The remaining distillation bottoms are clarified in a decanter. The supernatant includes thin stillage which contains protein. The underflow consists of a solid cake containing the coarse components of the grain. Part of the thin stillage is fed back into the mashing process (backset). The supernatant with the proteins and the yeast is thickened into a syrup in an evaporator. The evaporated water can be reused as boiler water, for example. The syrup is mixed with the solid material from the decanter again and dried to form DDGS (dry distiller‘s grain with solubles) which is used as a valuable feed.