Overview of the soybean process in the crushing industry☆

A minimal residual oil content in the meal coming out of the hexane extractor is a clear benefit for a crushing plant; the more oil yield the better revenue for the crusher. In a modern and efficient extraction plant, a residual oil content ≤ 0.5% for soybean meal is expected. The first step for an efficient solvent extraction is a good preparation process; its optimization makes it possible to shape the seeds for effective leaching and washing of the oil. Preparation also goes through an optimized dehulling (warm or hot dehulling) allowing, in an economical way, to maximize the protein content. The seed flaking can optionally be complemented by expanding which permits rupture of a more efficient portion of the cell walls. Solvent extraction consists in washing the prepared material in a countercurrent multistage process to enable a reasonable quantity of solvent to extract a maximal amount of oil. Major progresses in solvent extraction relate to plant production capacity increases which propelled technological improvements. Following extraction, the solvent is distilled from the miscella and recovered. A mineral oil system absorbs the residual solvent out of the effluent air stream. A single integrated unit also called desolventizer/toaster/dryer/cooler removes the solvent, toasts the meal in order to control the anti-nutritional factors and reduces moisture and temperature to levels appropriate for storage and transport. Although today the industry is mostly based on the solvent extraction process, certain strict constraints in the environmental aspects suggest alternative processes to minimize hexane emissions and even the return to mechanical operations (for example full press) allowing to completely eliminate the use of solvent at the expense of lower efficiency.