Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/28/2007
Publication Date: 5/14/2007
Citation: Dickey, L.C., Cooke, P.H., Kurantz, M.J., Mcaloon, A.J., Parris, N., Moreau, R.A. 2007. Using microwave heating to determine optimal corn germ oil yield with a bench-scale press. 2007. Journal of the American Oil Chemists' Society 84(5):489-495. Interpretive Summary: Dry grind production of ethanol from corn creates a byproduct, distillers’ dried grains, that contains the embryo of the kernel, also called the germ. The germ which contains > 90% of all the oil in the kernel, can be separated from the corn prior to fermentation by several new processes and then oil can be separated from the germ and made available to consumers, keeping the vegetable oil price stable despite likely increased use for biodiesel production. Sale of germ as a byproduct, in place of some of the distillers’ dried grains, should significantly reduce the overall cost of producing ethanol and benefit this industry. More dry grind ethanol production will bolster the U.S. corn market, reduce petroleum imports and slow depletion of world petroleum supplies. The germ price and its impact on dry grind plant profitability will increase if the cost of removing the oil from the germ can be reduced. This study shows that 65% of the oil can be pressed from heated germ at practical rates. We use the production rate to show that an oil expeller plant will need germ from several typical size dry grind plants to be economical.
Technical Abstract: Methods have been proposed recently to separate germ from corn prior to fermentation to improve dry grind ethanol process economic return. Oil would be extracted from the germ and sold as a separate product. It is not clear that available methods to extract oil from this germ are economically practical. Corn germ was preheated in a microwave oven and oil was then extracted with a bench-scale press. Preheating improved the yield obtained for the press used and allowed prediction of optimum conditions obtainable by larger presses. Microwave heating appeared to heat oil in the germ more quickly than the other components of the germ, as indicated by microscopic inspection of heated germ specimens. Less oil could be pressed from germ initially containing 3-6% moisture than germ containing 15-20% moisture. For the wetter germ, oil recovery generally increased with increased microwave heating time until the heated germ moisture reached 6%. A maximum oil recovery of about 65% was obtained for all germs tested when the optimum expeller temperature/germ feed moisture was used. For a commercial expeller moisture would be added to minimize cooling of the expeller. Using the maximum oil recovery from the pressing experiments a commercial cost for expressed corn oil can be estimated from soy oil plants. The cost advantage of a larger pressing facility recommends pressing the germ output of several dry grind ethanol plant of average size. Feasibility of expelling germ from several plants is not endangered by the likely necessity of drying the germ for temporary storage since we found that rehydrating germ that had been dried to optimum moisture for pressing did not reduce pressed oil yield.