Refining of oils and fats

The technique of continuous refining of oils and fats has steadily improved since the first commercial installation some 30 years ago. Refining is the most important economic factor in the overall processing of an oil from the crude to the finished product. Crude oil handling, reagent selection, mixing, heating, and centrifugal separation are all critical when an attempt is made to obtain the maximum refining efficiency. The agronomist, scientist, control laboratory and operating personnel, along with the equipment manufacturers, have all aided in obtaining more efficient and economical processing methods. In a discussion of the over-all refining process, soapstock handling must also be considered. In recent years several successful continuous soapstock acidulation plants have been installed. With this addition to a refinery, the refining operation can now truly be considered as a continuous process. Like most industrial processes, this has been an evolution from the batch system to a semicontinuous system up to the present continuous treatment of soapstock and wash water to produce a high-purity acid oil on an economical basis. Details of the various factors in refining and aeidulation on a commercial basis, along with control methods, are discussed. Presented at the AOCS Short Course, “Processing Quality Control of Fats and Oils,” East Lansing, Mich., Aug. 29–Sept. 1, 1966.     

Refining and degumming systems for edible fats and oils

Crude edible fats and oils contain variable amounts of nonglyceride impurities, such as free fatty acids, non-fatty materials generally classified as “gums”, and color pigments. Most of these impurities are detrimental to end product fresh and aged quality characteristics, hence must be eliminated by a purification process before the finished fats and oils are suitable for human consumption. The object of this process is to remove these objectionable impurities with the least possible loss of neutral oil and tocopherals. Key theoretical and practical factors for degumming and refining crude edible oils are discussed with particular reference to processes, flow charts, control systems and analytical testing requirements. In addition to typical large volume oils, such as soya and cotton, techniques are also reviewed for smaller volume oils, including palm, lauric and corm.     

Degumming,refining, bleaching,and deodorization theory

Basic theory and principles of degumming, refining, bleaching, and deodorization are reviewed. Composition of crude oils, hydration of ions and molecules, neutralization of organic acid, and separation and modification of products by centrifugation, adsorption, and vacuum steam distillation are briefly summarized. Reactions of vegetable oils include hydration, neutralization, and oxidation.     

Degumming,refining and bleaching soybean oil

This subject deals with the removal of the fat-soluble impurities from crude soybean oil. These impurities may be present in true solution or in a colloidal state; their effective removal is necessary to achieve quality standards for end-use products. The processing step options for the removal of these impurities in any given situation are easily defined; the conditions and practices used, however, are the primary concern of this paper. International trading of soybean oil mandates the degumming step. The increased use of import/export soybean oil increases the importance of this processing practice. Pretreatment and effective contact time are the critical issues. Refining, as a specific process, deals primarily with free fatty acid removal, with or without simultaneous degumming as a single-step operation. State-of-the-art wet, chemical refining practices are described, and the current limitations and future opportunities for the physical refining of soybean oil are discussed. The importance of the bleaching step cannot be overstated and it should be noted that color reduction is only coincidentally achieved. The primary function of the bleaching process is to remove oxidative breakdown products, and the degree or level of treatment should be consistent with that objective. Underbleaching and thermal decolorization (deodorization) of soybean oil are misguided practices. Once “cleaned-up” through adequate bleaching, an oil should be guarded against thermal/oxidative abuse.