3.2.1.1 Dry Mill Process versus Wet Mill Process

Ethanol production facilities can be classified into two broad types: wet mill­ing and dry milling operations. As the term "dry" implies, the dry milling process first grinds the entire corn kernel into flour which is referred to as "meal" or "corn meal." Dry mills are usually smaller in size (capacity) and are built primarily to manufacture ethanol only. The remaining stillage from ethanol purification undergoes a different process treatment to produce a highly nutritious livestock feed. Wet mill facilities are called "corn refiner­ies," and also produce a list of high-valued coproducts such as high-fruc­tose corn syrup (HFCS), dextrose, and cornstarch. Both wet and dry milling operations are currently used to convert corn to ethanol. Wet milling is usu­ally a larger and more versatile process, and could be valuable for coping with volatile energy markets. Wet milling can be used to produce a greater variety of products such as cornstarch, corn syrup, ethanol, dry distillers grains, artificial sweeteners like Splenda®, and more. Although wet milling is a more versatile process and offers a more diverse product portfolio than dry milling, when producing fuel ethanol, dry milling has higher efficiency and lower capital and operating costs than wet milling. Most of the recent ethanol plants built in the United States are based on dry milling operations [13]. As of the end of 2008, a total of 86% of corn ethanol in the United States was commercially produced using the dry mill process using a total of 150 dry milling plants [14].