Olive Processing by the Centrifugation System in Big-sized Oil Mill: Effects on Oil Yield and Quality and on the Economy of the Process.
L. Di Giovacchino, S.M. Preziuso, M.G. Di Serio, G. Di Loreto, M.R. Mucciarella
CRA–OLI Centre of Città S. Angelo (PE) - Italy

In recent years, in Italy, some big-sized oil mills, equipped with centrifugal decanters at high loading capacity, with the aim to reduce the costs, have adopted the diagram of the double extraction of oil, recovering also the stone fragments from olive pomace. To ascertain the economic and qualitative results, experimental tests were carried out in a big-sized oil mill, located in Puglia region, where olive fruits of Coratina variety were processed according to the following technological diagrams:
•	Line A: olive crushing by the coupled method millstones-metallic crusher; olive paste malaxation; first extraction of oil by a 2-phases decanter; separation of stone fragments from the residual olive paste; extraction of oil by a second centrifugation (at 3-phases) of the de-stoned olive cake.
•	Line B: olive crushing by a metallic crusher at fixed hammers; olive paste malaxation; first extraction of oil by a 2-phases decanter; separation of stone fragments from the residual olive paste; extraction of oil by a second centrifugation (at 3-phases) of the de-stoned olive cake.
The results indicated that the average oil yield of the first centrifugation was 86.1 % (Line A) and 85.2% (Line B), whereas the oil yield of the second centrifugation was, on average, 3 kg/t of olives. The oil of the first extraction was extra virgin, very good in quality, and, when the coupled method millstones-metallic crusher was used (Line A), it had a higher content of volatile substances at C6, derived from the linolenic acid by the lipoxygenase pathway. When the metallic crusher at fixed hammers was used (Line B), instead, the oil of the first extraction had a higher content of total phenols and, in particular, of secoiridoids. The oil of the second extraction, even if good in quality, had an anomalous composition with regard to the percentage of the triterpenic di-alcohols only. The recovery of stone fragments from olive paste, obtained after the first centrifugation, was about 0.12 t/t of olives, that represented an interesting income for oil mill because of their value as fuel at medium-high thermal power.