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Distillers Dried Grains with Solubles (DDGS)

Currently corn grain is the primary biological material that can be economically converted into ethanol on an industrial scale. The corn-based fuel ethanol industry is poised to produce substantial quantities of biofuel during the coming century as this industry continues its rapid expansion. The number of corn ethanol plants, and their processing capacities, has been markedly increasing in recent years. For example, at the end of 2005, 97 manufacturing plants in the U.S. had an aggregate production capacity of nearly 16.3 billion L/y (4.3 billion gal/y), which represents a growth of 226% over the previous five year period. More information on the growth of this industry can be found in Lyons (2003), BBI (2006), and RFA (2006).

Bioethanol manufacturing from corn grain results in three main products: bioethanol, the primary end product; residual nonfermentable corn kernel components, which are typically marketed as “distillers grains” (Figure 1); and carbon dioxide. Anecdotally, the rule of thumb commonly used in industry states that for each 1 kg of corn processed, approximately 1/3 kg of each of these constituent product streams will be produced. The production process consists of several steps, including grinding, cooking, liquefying, saccharifying, fermenting, and distilling the corn grain.

The nonfermentable residues are removed from the process stream during the distillation stage in the form of whole stillage. They are centrifuged and dried, to ensure a substantial shelf life, and then sold as distillers grains (most commonly as DDGS – “dried distillers grains with solubles”) for feed rations to local livestock producers, or shipped via truck or rail for use by distant customers. The sale of distillers grains contributes substantially to the economic viability of bioethanol manufacturing, and is thus a vital component to each plant’s operations. Hence the nutritional content and quality of distillers grains is important to ethanol processors. Several studies have thoroughly examined chemical and nutritional properties of these byproduct feeds, including Belyea et al. (1998), Belyea et al., (2004), Shurson et al. (2004), and Spiehs et al. (2002). Rosentrater et al. (2005) comprehensively reviewed much of the available chemical and nutritional research.

To date, however, no studies have examined the physical properties of distillers grains. Property data are not only essential for livestock diet formulation, but also for the design and optimization of material handling systems, various unit operations, processing facilities, and storage structures. As this industry continues its rapid growth, it is imperative to establish baseline information from which engineers and scientists can work. Toward this end, it is the goal of this project to provide such information. The specific objective of this paper is to report initial findings for some of the physical properties of DDGS that have been determined to date, including moisture content, water activity, thermal properties, bulk density, angle of repose, and color.

Physical propertiesEdit

nminmaxmeans.d.reference
Moisture content (%, d.b.)7213.2121.1614.721.52Rosentrater, 2006
Water activity (-)720.5270.6340.5520.021Rosentrater, 2006
Thermal Conductivity (W / m °C)720.060.080.070.01Rosentrater, 2006
Resistivity (m °C / W)7213.1015.6014.000.52Rosentrater, 2006
Diffusivity (mm2 / s)720.130.150.130.01Rosentrater, 2006
Bulk density (kg / m3)72389.28501.46483.2724.12Rosentrater, 2006
Angle of Repose (deg)7226.5134.2331.481.81Rosentrater, 2006
Color
Hunter L (-)7239.9949.8243.131.62Rosentrater, 2006
Hunter a (-)728.009.818.690.38Rosentrater, 2006
Hunter b (-)7218.2223.5019.370.93Rosentrater, 2006

Table 2. Correlation coefficients (r) between physical properties of DDGS and (associated p values; significance level of 0.05).

Moisture Content Water Activity Conductivity Resistivity Diffusivity Bulk Density Angle L a b Moisture Content 1.000 --- Water Activity -0.053 1.000 (0.661) --- Conductivity 0.064 -0.443 1.000 (0.590) (0.000) --- Resistivity -0.091 0.679 -0.643 1.000 (0.447) (0.000) (0.000) --- Diffusivity 0.025 0.634 -0.414 0.828 1.000 (0.835) (0.000) (0.000) (0.000) --- Bulk Density 0.074 -0.932 0.414 -0.709 -0.671 1.000 (0.538) (0.000) (0.000) (0.000) (0.000) --- Angle -0.329 0.040 -0.097 0.049 -0.026 -0.097 1.000 (0.005) (0.739) (0.415) (0.684) (0.826) (0.418) --- L -0.253 0.729 -0.323 0.570 0.476 -0.784 0.198 1.000 (0.032) (0.000) (0.006) (0.000) (0.000) (0.000) (0.095) --- a 0.043 0.697 -0.243 0.393 0.473 -0.731 -0.075 0.435 1.000 (0.720) (0.000) (0.040) (0.001) (0.000) (0.000) (0.532) (0.000) --- b -0.247 0.832 -0.375 0.568 0.520 -0.886 0.236 0.917 0.640 1.000 (0.036) (0.000) (0.001) (0.000) (0.000) (0.000) (0.046) (0.000) (0.000) ---

ReferencesEdit

ASAE Standards, 51st ed. 2004. S352.2: Moisture measurement – Grains and seeds. St. Joseph, Mich.: ASAE. Baghe-Khandan, M., S. Y. Choi, and M. R. Okos. 1981. Improved line heat source thermal conductivity probe. Journal of Food Science 46(5): 1430-1432. BBI. 2006. U.S. Production Capacity. Existing Plants. BBI International: Grand Forks, ND. Available online: http://www.bbiethanol.com/plant_production/uspc.html [Accessed 11 February 2005]. Belyea, R. L., S. Eckhoff, M. Wallig, and M. Tumbleson. 1998. Variability in the nutritional quality of distillers solubles. Bioresource Technology 66: 207-212. Belyea, R. L., K. D. Rausch, and M. E. Tumbleson. 2004. Composition of corn and distillers dried grains with solubles from dry grind ethanol processing. Bioresource Technology 94: 293-298. Dien, B. S., R. J. Bothast, N. N. Nichols, and M. A. Cotta. 2003. The U.S. corn ethanol industry: an overview of current technology and future prospects. In The Third International Starch Technology Conference – Coproducts Program Proceedings, eds. M. Tumbleson, V. Singh, and K. Rausch, 2-4 June, 2003, University of Illinois, pp. 10-21. Everitt, B. S., and G. Dunn. 1991. Applied Multivariate Data Analysis. New York, NY: Halsted Press. Hunter Associates Laboratory. 2002. Universal Software User’s Manual, Version 2.5. Reston, VA: Hunter Laboratory Associates. Jaques, K. A., T. P. Lyons, and D. R. Kelsall. 2003. The Alcohol Textbook. Nottingham University Press: Nottingham, UK. Lyons, T. P. 2003. Ethanol around the world: rapid growth in policies, technology, and production. In The Alcohol Textbook, K. A. Jaques, T. P. Lyons, and D. R. Kelsall, eds. Nottingham University Press: Nottingham, UK. Mohsenin, N. N. 1980. Physical Properties of Plant and Animal materials, Vol. I – Structure, Physical Characteristics, and Mechanical Properties. Gordon and Breach Science Publishers, New York, NY. RFA. 2006. Homegrown for the Heartland – Ethanol Industry Outlook. Washington, D.C.: Renewable Fuels Association. Rosentrater, K. A., K. Muthukumarappan, J. Julson, and P. Krishnan. 2005. Update on Ethanol Processing Residue Properties. ASAE Paper No. 056024. St. Joseph, MI: ASAE. Tibelius, C. 1996. Coproducts and Near Coproducts of Fuel Ethanol Fermentation from Grain. Agriculture and Agri-Food Canada – Canadian Green Plan Ethanol Program: Starchy Waste Streams Evaluation Project. Available online: http://res2.agr.ca/publications/cfar/index_e.htm [Accessed 01 February 2005]. Shurson, G. C., M. J. Spiehs, and M. Whitney. 2004. The use of maize distiller’s dried grains with solubles in pig diets. Pig News and Information 25(2): 75N-83N. Speigel, M. R. 1994. Statistics. New York, NY: McGraw-Hill, Inc. Spiehs, M. J., M. H. Whitney, and G. C. Shurson. 2002. Nutrient database for distiller’s dried grains with solubles produced from new ethanol plants in Minnesota and South Dakota. Journal of Animal Science 80: 2639-2645. UMN. 2005. The Value and Use of Distillers Dried Grains with Solubles (DDGS) in Livestock and Poultry Feeds. University of Minnesota. Available online: http://www.ddgs.umn.edu/. [Accessed 01 May 2005]. USDA. 1999. Practical Procedures for Grain Handlers: Inspecting Grain. United States Department of Agriculture – Grain Inspection, Packers, and Stockyards Administration: Washington, D.C. Available online: http://web.archive.org/web/20051210170220/http://151.121.3.117/pubs/primer.pdf [Accessed 01 February 2005]. Weigel, J. C., D. Loy, and L. Kilmer. 1997. Feed Co-Products of the Dry Corn Milling Process. Iowa State University, Iowa Corn Promotion Board, Iowa Department of Agriculture, Renewable Fuels Association, National Corn Growers Association. Available online: www.iowacorn.org/ethanol/ethanol_17.html [Accessed 01 February 2005].

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