🏭 Olive harvest and the oil mill

Olive harvest and the oil mill covers the fruit's journey from tree to bottle: picking, delivery to the mill, oil extraction, the preparation of table olives, and the trades involved.

Olives for oil are harvested from October to April in the Northern Hemisphere and from April to July in the Southern. Until the 1980s olives were picked by hand everywhere: one picker gathers about 80 kg a day, and hand labour takes 50–60% of field costs. Today trunk and branch shakers with «umbrellas» and nets do much of the work, and hedgerow groves are picked by an over-the-row harvester in about 3–4 hours per hectare.

Oil should be extracted within 1–3 days of picking, otherwise acidity rises; the specifications of 50 Italian DOP and IGP oils allow the fruit to be stored for 24–120 hours, most often 48. At the Olive oil mill the leaves are removed and the fruit is washed, followed by Olive crushing, Malaxation, decanting and separation. The world has about 12,000 mills, and more than 80% use centrifuges. A Decanter centrifuge can be three-phase, needing 40–60 litres of warm water per 100 kg of olives, or two-phase, with no added water.

Cold pressing has strict limits: in the EU, «first cold pressing» may only appear on oil from a hydraulic press at below 27 °C. According to a 2015 IOC study, the average oil yield is 17–20%, so roughly 5–6 kg of olives go into 1 kg of oil.

In the grove works the Olive grower, at the mill the Olive mill operator, and quality is judged by the Olive oil taster. Table olives need Brine and Sodium hydroxide (lye), which converts the bitter oleuropein.