Degumming and refining practices in Europe

European practices for degumming and refining various vegetable oils are reviewed. Special attention is given to specific processes differing from those commonly used in the U.S. and to the practical problems of day-to-day operations.     

Bleaching practices in the U.S.

The differences between European and U.S. vegetable oils with respect to their influence on bleaching requirements are discussed. Based on the information supplied by over 50 refiners, a summary gives an insight into bleaching conditions with earth and heat. These data are condensed in a chart relative to most used oils and fats. General information on pre-and post-bleach is also indicated.     

Degumming,dewaxing and refining

Degumming, dewaxing and refining are aimed at removing certain fat-soluble impurities. The different operations can be done separately or in various combinations depending on, e.g., the type of feedstock and the desired refining result. State-of-the-art of water degumming and chemical (alkali) refining are discussed with special emphasis on quality and yield of products and byproducts. Dewaxing, which is of special interest for some oils such as sunflower oil, maize oil and ricebran oil, can be performed either by a filtration process or by centrifugal separation in connection with water degumming or alkali refining.     

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.     

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.     

Current practices in continuous cottonseed miscella refining

Miscella refining of crude cottonseed oil has become a generally accepted commercial process for the past 20 years. The simple and efficient continuous process for removal of undesirable impurities is described, having changed little in its basic form since discovery 40 years ago. The individual unit processes, control systems, process flow charts, chemical reactions and oil-to-hexane ratios used in miscella refining are described. The several advantages to miscella refining vs conventional oil refining are noted.     

Finished oil handling and storage in the U.S.

Various techniques are practiced in the U.S. to prevent deterioration of vegetable oils following the final stage of processing through deodorization. Because oxidation; free fatty acid development, or adulteration by impurities are the primary concerns, the general practice is to keep oils in closed vessels in an atmosphere that excludes oxygen and moisture and where temperatures are controlled at minimum levels. The technology of sparging and blanketing finished oils with nitrogen during storage and transfer from vessel to vessel is shown. Also, a typical blanketing system for a series of vessels, pressure controllers, and techniques to avoid vacuum conditions is described.     

U.S. Soybean industry

Journal of the American Oil Chemists' Society -