14 A Primer oils Processing Technoloty or adjusts the speed of extractor to keep the baske as full possible, with typical total retention me in the extractor of 30 45 min. After ciher drops, or in the case of t ecreened basket diiringe, basket bottom design, has an opening strategically placed to allow stationary the solid phase to discharge. As the extracted material drops, the sereen is closed, and the cycle begi anew. Extracted material is kept a discharge equipment In this manner hopper prior to conveying to the equipment while the plug of a continuous flow is provided to downstream desolventizer-toaster material in the hopper helps prevent the possibility of (DT) sparge steam from entering tie extractor. Shallow-bed extractors, with bed depths generally less than 1 m. provide material similar drainage screens in the orm of slotted bars. The oil-bearing conveyed through zones in the extractor where e counter cur- is continuously rent washing of miscella occurs. At the discharge end of the extractor t hite flake material is dropped into a hopper and is conveyed to the desolvent- Shallow-bed extractors have gained significant ed control. are popularity izing system. recent years and, as they lend themselves very we well suited for modern programmable logic control (PLC)-based operations Temperature control is extremely important during the extraction pr As extractibility is enhanced with high temperatures, perator genera desires to keep temperatures as high as possible without flashing the solvent or creating excess pressure in the extractor. However, enzyme phospholiapase activity affects the quality at these elevated conditio par temperature while this trade-off nonhydratable tially causing an increase phosphatides. is generally not a problem. when processing sacrificing residual fats somewhat field-damaged seed it may be necessary to reduce extraction hat can be acceptably processed temperature, order to produce an undue refining losses. As mentioned earlier. several processes have been developed to help inactive enzyme activity prior to extraction. While hexane is widely ecepted as the most effective solvent used today there are concerns about its flammab exposure, and environmental im pacts. Research has focused on various alternative solvents in the hopes of performance while providing finding one with acceptable greatersafety. Alter native solvents that have received some attention include isopropyl alcoho supercritical carbon dioxide. and other fluids. However, no economical alterna tive to n-hexane has been accepted at this point, and the best available control containment and limiting fugitive hexane emissions emphasizes technology The extracted white flake material. containing around 25-35% residual solvent, is conveyed from the extractor to the Dr. In the traditional system steam is used to countercurrently flash the volati solvent from the solid phase. The vapor phase then passes through the distillation system on its way to condensing and collection. The desolventized meal contains a high amount of urease activity (measured as a pHrise) that is detrimental for certain anima feeding purposes. Under conditions of heat, moisture, and retention time this enzyme is inactivated. and these variables provide the basis of control for the