Research Article Double extraction of olive oil in large oil mills of Southern Italy: Effects on extraction efficiency, oil quality, and economy of the process Luciano Di Giovacchino, Serena Maria Preziuso, Maria Gabriella Di Serio, Maria Regina Mucciarella, Giuseppina Di Loreto and Barbara Lanza Council for Agricultural Research and Economics (CREA), CREA-OLI Olive Growing and Oil Industry Research Centre, Citt a Sant’Angelo (PE), Italy In recent years, in Italy, some large oil mills, equipped with centrifugal decanter at high loading capacity have adopted the complex diagram of the double extraction of oil and, in addition, have been supplied with suitable machine to recover part of stone fragments from olive pomace with the aim to reduce the costs. Our experimental tests were carried out in a large oil mill, located in Apulia region, which processes olives of Olea europaea L. “Coratina” cultivar by double centrifugation of olive pastes prepared by using the double crushing (millstones and metallic crusher) or the single crushing (metallic crusher). The results showed that the oil yield of the first extraction was high (between 85 and 86%), regardless to the method used for olive crushing. The quality of virgin olive oil of the first extraction was extra virgin with some differences due to the different batches of olives and, in part, also to the used crushing methods. The oil of the second extraction was recovered in a low quantity (0.3 kg/100 kg olives) and its composition was not normal only for the percentage of triterpene dialcohols. The recovery of stone fragments was satisfying (about 0.13 t/t olives) and helped to significantly increase the income of oil mill. Practical applications: The double extraction of oil, by the centrifugation system, and the recovery of SF allow to reduce the costs of olive processing in medium-big sized oil mills. The second centrifugation, which permits to recover about 3 kg of oil/t of olives, and the recovery of SF, suitable to sell as fuel, allow to increase the income of oil mill. Keywords: Double extraction of oil / Oil mill by-products / Olive processing / Olive stone fragments / Virgin olive oil quality Received: April 7, 2016 / Revised: October 11, 2016 / Accepted: October 26, 2016 DOI: 10.1002/ejlt.201600161 1 Introduction In Italy, olive processing to mechanically extract virgin olive oil is carried out in many small-medium sized oil mills equipped with the pressing system (about 30%), or with the three-phases centrifugation system (about 70%). The high number of oil mills (more than 4000), present in almost all Italian regions and, especially, in the Southern regions where most of olive production is concentrated, makes the olive processing possible also in the zones where the production is small, but widespread and fragmentary. Therefore, the oil mill sector has high costs, also due to the following reasons: the daily olive processing capacity of many oil mills is very small, lower than 15 t/day; the requirement to process separately each olive lot of different farmers; the reduced quantity of each lot, commonly lower than 1 t; the use of the pressing system which is more expensive for the manpower cost; the use of the three-phases centrifugation system which requires the addition of water to olive paste and produces, as by-products, olive mill wastewater (OMW) and a wet olive pomace (WOP), that has a low content of oil and high content of moisture and, therefore, a low market value. However, in the regions at high olive production, like Apulia Correspondence: Barbara Lanza, Council for Agricultural Research and Economics (CREA), CREA-OLI Olive Growing and Oil Industry Research Centre, Viale Petruzzi 75, I-65013 Citt a Sant’Angelo (PE), Italy E-mail: barbara.lanza@crea.gov.it Fax: þ39-085-959518 Abbreviations: OMW, olive mill wastewater; OP d , de-oiled olive paste; OP s , stoned olive paste; SF, olive stone fragments; WOP, wet olive pomace Eur. J. Lipid Sci. Technol. 2016, 118, 0000–0000 1 www.ejlst.com ß 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim