1 - Extrusion/Expeller® Pressing as a Means of Processing Green Oils and Meals

Abstract

This chapter highlights the concerns for operating extruders and screw presses within constraints of green processing and within the constraints of organic foods. The green processing goal of having little or no impact on the environment should favor mechanical crushing and discourage solvent extraction because of solvent losses in effluent air and water stream. The chapter explains that today, most vegetable oils serving the food market are separated by solvent extraction because solvent extraction permits large capacity plants and maximum separation of oil. However, concerns about foods exposed to hexane and other chemicals may encourage food processors to favor some method other than solvent extraction where no hexane or other chemical solvent will be introduced to the food material being processed. Mechanical screw presses can meet this requirement, but screw presses have traditionally been low capacity machines compared to solvent extractors and consume more horsepower per ton of oil extracted than solvent extractors. Concerns related to green processing and organic feeds might become an incentive for equipment manufacturers to design screw presses for higher capacities, pressing to lower residual oils and consuming less horsepower. Significant work is already being done in these areas. Today's higher capacity full-presses operate at around 130 MT/d and produce residual oil levels of approximately 8%. A modest first step goal for some manufacturers is to supply full presses that can achieve 150 MT/d on canola pressing to 3% residual oil and achieving this goal is just around the corner.