EVALUATION OF SECOND EXTRACTION OF OLIVE OIL IN AUSTRALIA

In Australia, the widespread distribution of olive processing plants, their relatively small throughput and the absence of pomace treatment plants determines that the utilisation of the classical solvent extraction processes to recover the oil remaining in the olive-pomace is virtually impossible and economically unjustifiable. In Europe, and increasingly in other parts of the world, processing plants have been trying the partial extraction of the oil contained in the pomace from the first centrifugation using a second centrifugation. This process is possible if the processing plant has spare processing capacity, if it sets up additional processing lines for second extraction or if it stocks the pomace to be reprocessed at a later time. The objective of this project is to evaluate the technical and economical feasibility of reprocessing olive pomace both in small and large scale processing plants. The processing parameters studied were: re-processing delay, malaxing time and malaxing temperature. In a second extraction process carried out immediately after the first extraction the oil recovery was 37.4%. The increase in the delay between the first and second extraction did not provide significant increments in oil recovery. Malaxing time trials at constant temperature showed higher oil recoveries with longer malaxing times, whereas temperature trials at constant malaxing time did not show improvements in extractability with higher temperatures. A study of the chemical composition showed that the oil of all the project treatments fell outside any recognised categories according to international legislations for olive oil. The economic feasibility of second extraction practices was evaluated for each plant case.