Olive Oil Extraction

Olive Oil Extraction Christos Petrakis Mediterranean Agronomic Institute of Chania, P.O. BOX 85, GR-73100, Chania, Greece

Introduction Olive oil is the oily juice of the olive, separated from the other components of the fruit. Properly extracted from fresh, mature fruit of good quality, the oil has a characteristic sensory profile. Its fatty acid composition is characterized by a good balance between saturated, monounsaturated, and polyunsaturated acids. It is also unique among common vegetable oils in that it can be consumed in the crude form, thus conserving vitamin content and phenolic compounds of nutritional importance. According to the Codex Alimentarius, IOOC, and EC regulations: Virgin olive oil is the oil obtained from the fruit of the olive tree solely by mechanical or other physical means under conditions that do not lead to alteration in the oil, which have not undergone any treatment other than washing, decantation, centrifugation, or filtration, to the exclusion of oils obtained using solvents or using adjuvants having a chemical or biochemical action. e ideal objective of any extraction method is to extract the largest possible amount of oil without altering its original quality. However, if quality is not to be modified, it is essential to use only mechanical or physical methods for extracting the oil, avoiding chemical and enzymatic reactions that might change its natural composition. When treating the olive as prime material, one must consider two groups of phases: the solid elements of the skin, pulp, and kernel, and the liquid phases made up of the oil and the vegetable water. e preparation of olive oil is an industrial process, the purpose of which is to separate one of the liquid phases-the oil-from the other constituents of the fruit. us, beginning with healthy, whole, clean fruit, harvested at the moment of optimum maturity, it is necessary to make a paste preparation by means of breaking the vegetal structure; to liberate the oil from the cells and finally achieve the formation of solid and liquid phases. By means of pressure, percolation, or centrifugation, the solid and liquid phases are then separated. Finally, the liquid phases are separated into oil and vegetable water by decantation and/or vertical cen-

trifugation. e separation between the solid and the liquid phases is not complete: the mass of solids with varying percentages of humidity and oil content form the sub-product called olive pomace and the liquids with varying percentages of fine solid material constitute the oily must. Extraction methods became more effective with the use of hydraulic presses and transmission mechanisms. Over the years they became more and more mechanized, driven by the need to spare labor expenses in order to lower costs, but the whole process was discontinuous. e first tests conducted on continuous-flow facilities date back to the second half of the 1960s by Alpha Laval. Improvements enabled the oil to be extracted through the centrifugal effect produced by devices rotating at high speed; the use of stainless steel instead of ordinary steel raised the quality and hygiene standards of the oils produced. These facilities exploit the effect of centrifugal force, which operates by drawing off the liquids. When they came into use after years of testing, they helped to lower labor costs and raise processing capacity. e extraction of olive oil commences from the olive tree and ends with the storage of the product. ere are limitations in a series of factors prior to the extraction process which influence the quantity and quality of the oils. e main factors (which are beyond the scope of this chapter) are: the varieties of the olives, the microclimatic conditions, the variability of soils, the systems of cultivation, which regulate the absorption capacity of terrains and retain rain or irrigation water (Montedoro et al., 1989, 1992; Inglese et al., 1996; Reiners et al., 1998; Gutierrez et al., 1999; Tovar et al., 2001; Romero et al, 2002; Morello et al., 2003; El Antari et al., 2003; Servili et al., 2004; Royo et al., 2005); and pest monitoring and control (Zunin et al., 1993).