Com wet mill process

Johnston, D.B. and Singh, V. 2001. Use of proteases to reduce steep time and S02 requirements in a com wet-milling process. Cereal Chem. 78, 405—411. 

Corn steep liquor (CSL), a byproduct of the com wet-milling process, was used in an immobilized cell continuous biofilm reactor to replace the expensive P2 medium ingredients. The use of CSL resulted in the production of 6.29 g/L of total acetone-butanol-ethanol (ABE) as compared with 6.86 g/L in a control experiment. These studies were performed at a dilution rate of 0.32 hr1. The productivities in the control and CSL experiment were 2.19 and 2.01 g/(Lh), respectively. Although the use of CSL resulted in a 10% decrease in productivity, it is viewed that its application would be economical compared to P2 medium. Hence, CSL may be used to replace the P2 medium. It was also demonstrated that inclusion of butyrate into the feed was beneficial to the butanol fermentation. A control experiment produced 4.77 g/L of total ABE, and the experiment with supplemented sodium butyrate produced 5.70 g/L of total ABE. The butanol concentration increased from 3.14 to 4.04 g/L. Inclusion of acetate in the feed medium of the immobilized cell biofilm reactor was not found to be beneficial for the ABE fermentation, as reported for the batch ABE fermentation. 

Volume 4 Technology of Com Wet Milling and Associated Processes (by P.H. Blanchard)... 

In 2002, approximately 2.2 billion bushels of corn were processed in the United States for the production of food, fuel, and industrial products. Of that 2.2 billion bushels, 19.22 million tonnes (757 million bushels) were used for high fructose corn syrup (HFCS), glucose and dextrose, 6.34 million tonnes (250 million bushels) for pearl starch, 26.69 million tonnes (1051 million bushels) for fuel and beverage alcohol, and 4.75 million tonnes (187 million bushels) for cereals and other products (Corn Refiners Association, 2003). More than 50% of the com processed in the United States is done so using the corn wet milling process. 

The corn wet milling process involves taking apart a corn kernel into its individual components. To take apart a com kernel for maximum and high-quality starch recovery, it is important to understand the structure and composition of the corn kernel. 

Steeping and wet-milling processes are also utilized to separate soluble compounds from com. One process involves removal of soluble starch and protein from com by steeping com in a warm sulfurous acid solution for about one to two days. The undissolved com solids are then coarsely wet-milled and processed to collect the oil-containing germ for com oil production. Also, for more enzyme-resistant cellulose biomass, sulfuric acid or hydrochloric acid can be used to digest the cellulose polysaccharide into fermentable molecules. 

Com refining plants tend to be located near sources of raw material. In 1992, nearly 75% of the US com wet-milling industry value of shipments was from plants located in Iowa, Indiana and Illinois.1 In the early 1990s, these three states accounted for about 45% of US corn production. Processing plants in the Com Belt are substantially larger than those in locations away from major corn producing areas. 

The chapter on com and sorghum starch production not only thoroughly covers advances in understanding and in carrying out the wet-milling process, but also alternative com kernel fractionation techniques, the relationship of starch production to other products from com grain and future directions. 

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