Production of Pomace Olive Oil
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GRASAS Y ACEITES, 57 (1), ENERO-MARZO, 47-55, 2006, ISSN: 0017-3495 Production of pomace olive oil By Pedro Sánchez Moral1 and Mª Victoria Ruiz Méndez*2 1 Oleícola el Tejar. Ntra. Sra. de Araceli, SCA. Benamejí (Córdoba) 2 Instituto de la Grasa.CSIC. Avda. P. García Tejero, 4. 41012-Sevilla *to whom correspondence should be addressed RESUMEN Until about 30 years ago, almost all olive oil was obtained through pressing. In the 70s, the mills Obtención de aceite de orujo gradually abandoned the traditional olive pressing El aceite de orujo es el principal subproducto en el process for economical reasons, because the procesado de aceite de oliva y su obtención se ha method is labour intensive. Nowadays the transformado considerablemente en los últimos tiempos traditional method is only used for processing small debido a los avances tecnológicos que han experimentado las quantities of ecological olive oil. The alternative almazaras. Este trabajo tiene la finalidad de presentar una method is the continuous system works by means panorámica de la complejidad de este sector, de casi 100 años of the centrifugation of the beaten olive paste, de existencia, que se afana en encontrar su función dentro de la nueva estrategia integral de la industria oleícola después de producing three products: oil, pomace and residual la crisis sufrida en el año 2001. En el mismo se comentan la water, just like the pressing system. extracción física, el secado, así como la extracción con During the 90s, there was a major change in the disolvente, y la influencia que tienen los tratamientos raw material arriving at the olive pomace oil tecnológicos sobre la composición química del aceite de orujo. extractors. This was due to the fact that a large number of Spanish mills changed the olive oil PALABRAS-CLAVE: Aceite de orujo – Extracción con solvente – Extracción física – Procesado – Secado. continuous extraction equipment, converting from the three phase to the two phase system in order to optimize extraction costs and prevent the SUMMARY production of a highly polluting residual wastewater. At present, three types of olive pomaces can be Production of pomace olive oil considered, depending on the extraction system Pomace oil is the principal by-product in olive oil used on the olive: processing and is currently developing considerably due to the technological advances which the mills have undergone in – Pomace from pressing. recent years.This investigation aims at presenting an overview – Pomace from the continuous system with of the complexity of this sector which, with around 100 years centrifugal separation in three stages (oil, of existence, is searching for a role in the new integral strategy residual water and pomace), hereinafter of the olive oil industry after the crisis suffered in 2001. referred to as “pomace from the three-phase Physical extraction, drying and solvent extraction are process”. discussed, along with the influence of the technological treatments on the chemical composition of pomace oil. – Pomace from the continuous system with centrifugal separation in two stages: oil and KEY-WORDS: Drying - Physical extraction – Pomace solid waste (in which the olive vegetation olive oil – Processing - Solvent extraction. water from the olive is absorbed, and olive mill wastewater is not produced since water is not required in the centrifugal process), 1. INTRODUCTION hereinafter referred to as “two-phase pomace” (Alba et al., 1996). Olive pomace is the solid by-product obtained from the extraction of olive oil. It consists of pieces The main differences between the extracted raw of skin, pulp, stone and olive kernel. Of the total materials are due to water content. Two-phase olive weight, the pulp forms about 70 – 90 %, the pomace has moisture close to 70% and contains a stone 9-27% and the seed about 2-3%. The certain amount of sugars as a result of the removal of by-products from oil mills by pomace oil presence of vegetation water, while traditional extractors totally solves the environmental pomace has a moisture content of between 25 and problems caused by the olive oil production 30% in the pressing system, and 45% in 3-phase process. Similarly, the pomace oil extraction — centrifugal systems. refining — bottling —distribution chain plays a This leads to the need to modify the basic decisive role in the economic activity of the sector operations of transportation, storage and drying, (10 % of Spanish final agricultural production). making processing more expensive while at the same 47 PEDRO SÁNCHEZ MORAL AND Mª VICTORIA RUIZ MÉNDEZ time reducing the profits rendered from fatty material. require different preconditioning procedures than The changes produced in pressed olive pomace those coming from two phases pomaces prior to their during storage were closely studied from either extraction with solvent. chemical (Gracian el al., 1961) or microbiological Figure 1 shows the block diagram of the (Gracian et al., 1962 ) points of view. treatment for pressed pomace or pomace from the According to the traditional method, pomace oil three-phase process, where the pneumatically is extracted from a dried pomace (8% moisture removal of the stone is done just after drying. The approximately) with solvent. The product obtained is stone is separated, in the majority of cases, using the so-called “crude pomace oil”. separating machines where the air which flows On the other hand, if the fresh or stored two-phase against the pomace current pulls off the lighter pulp pomace is subjected to a second centrifugation, it is particles, leaving behind the heavier and larger possible to extract between 40 -60% of the retained stone pieces. To separate the pulp from the air flow residual oil The process is carried out using horizontal which carries it, cyclones are used, which enable centrifugal machines or decanters, (Alba et al., 1996). the air to be cleaned and emitted into the The oil obtained is known as “second centrifugation atmosphere. The pressed pomace and pomace oil” and is commercially classified for its properties as from the three-phase process must be directly “crude pomace oil”. subjected to a drying process immediately after Therefore, at present, two types of pomace oil leaving the mills in order to prevent the rapid are available: i) that extracted using solvents deterioration of the oil, particularly free acidity. (traditional), ii) the oil obtained through physical The other main difference between 3- phase extraction or centrifugation (second centrifugation). pomace and alperujo (pomace from the two-phase The current pomace from the two phase process) lies in the method of removing the stone. centrifugal system, due to its high water content, is Figure 2 shows the block diagram corresponding to stored in ponds situated outside the factories, the treatment of two-phase pomace in order to where it remains for up to 6 months, depending on obtain oil from this residue by using solvents. Stone the production capacity of the extractor. removal, as can be seen, is prior to drying and is The stored paste is of a heterogeneous nature carried out using mills with filters with approximately and many chemical compounds coexist with the oil 3mm spaces, which allow solids smaller than this released. Among them are metals, alkaline size to pass through, expelling the larger stone (potassium) and alkaline-earth (calcium and directly to the drying phase. This provides greater magnesium), sugars and polyphenols, which come yield in the physical extraction, reduced waste due from the vegetation water. The properties of the oil to the metal parts which rub directly against the obtained from this paste change as storage time paste to be extracted and better exploitation of the increases, since the paste on the surface of the resulting by-products. tank dries out. Quality deterioration is greater in oils Prior to separation by centrifugation, free of from pastes which have been centrifuged twice stone “alperujo” is then subjected to a malaxation and, in particular on the surface of the tanks or process. The beating equipment is similar to that ponds, and therefore these containers should have used in olive oil extraction. The temperature at which the lowest possible surface area/volume ratio. the centrifugation takes place is around 40°C. (Ramos and Ruiz-Méndez, 2004). In addition, free acidity increases with storage time in all cases, although it is higher in the paste taken 2. PHYSICAL EXTRACTION USING from the top layer of the ponds. The concentrations of CENTRIFUGATION the compounds produced during fermentation of the paste also increases over time, with the appearance The operating principle is similar to that for of methyl and ethyl esters, especially in pastes which obtaining olive oil. Separation takes place in a have been subjected to a double centrifugation and horizontal cylindrical rotor with a worm screw. The stored for long periods of time (over two months) pomace enters the rotor through an immobile input (Ramos and Ruiz-Méndez, 2004). pipe and is driven ahead by an inner rotor. The Pomaces from the traditional extraction system centrifugal forces cause the solids to sediment on (pressure) and those from the three phase extraction the rotor walls. The worm screw turns in the same Figure 1 Block diagram of the oil production from pressed pomace or 3-phase pomace 48 GRASAS Y ACEITES, 57 (1), ENERO-MARZO, 47-55, 2006, ISSN: 0017-3495 PRODUCTION OF POMACE OLIVE OIL Figure 2 Block diagram of the oil production from 2-phase pomace direction as the rotor, but at a different speed, Normally, drying takes place in rotary heat making the solids move towards the conical end of dryers (Espínola, 2003; Arjona et al., 1999, 2005) in the rotor. Separation takes place along the which both the product (pomace) to be dried and cylindrical part of the rotor, and the oil leaves the the hot drying gases are introduced at high rotor through adjustable plates on the casing.