How Olives Are Processed Into Oil

Extracting oil from the fruit of the olive tree is a com­plex process, a chal­lenge faced by the peo­ple of the Mediterranean for thou­sands of years.

Today, highly sophis­ti­cated elec­tron­i­cally-con­trolled milling equip­ment quickly replaces the large stone grinders used for cen­turies to crush olive dru­pes.

While these tra­di­tional mills are still widely used, the sec­tor’s con­tin­ued efforts to achieve the opti­mal organolep­tic char­ac­ter­is­tics and health prop­er­ties have seen the tech­nol­ogy used to pro­duce olive oil change rapidly.

The tech­nol­ogy behind the milling process

The incor­po­ra­tion of state-of-the-art tech­nol­ogy has paved the way for the increas­ing qual­ity of olive oil pro­duc­tion.

Producers can now tai­lor the trans­for­ma­tion process to their spe­cific needs, alter­ing oper­at­ing times, tem­per­a­tures, atmos­pheric com­po­si­tion, etc.

“Without these advance­ments, we would not have the extra­or­di­nar­ily high qual­ity of our olive oils,” Furio Battelini, the tech­ni­cal direc­tor of Agraria Riva del Garda, told Olive Oil Times.

“Much tech­nol­ogy is yet to be devel­oped, but it exerts a cru­cial role,” he added. ​“Whoever aims at high qual­ity in olive oil mak­ing needs to invest in it, try it out and find the best set­tings for their olives.”

Successfully pro­duc­ing the high­est-qual­ity olive oil heav­ily depends on agro­nom­ics, tech­nol­ogy and the expe­ri­ence of trained tech­ni­cians.

Whereas olive oil pro­duc­ers once har­vested all their fruits at once to trans­form them at the end of the har­vest, mod­ern pro­duc­ers often deploy spe­cific milling set­tings for the dif­fer­ent olive vari­eties they grow.

They can now explore the ripen­ing of the olive fruits to iden­tify the per­fect moment for trans­for­ma­tion. Each cul­ti­var is often har­vested and trans­formed in sep­a­rate moments.

First step: crush­ing the fruit

Once the olives reach the mill, the leaves left over from the har­vest are mechan­i­cally removed, and the fruits are washed.

In tra­di­tional mills, olives are crushed with a pro­ce­dure sub­stan­tially unchanged for cen­turies: heavy grinders attached to a cen­tral col­umn crush the fruits.

Modern mills use advanced machines with ham­mer break­ers, blades or rotary disks, allow­ing for a quicker trans­for­ma­tion of sig­nif­i­cantly larger amounts of olives.

Additionally, these tools greatly limit the expo­si­tion of the olives to oxy­gen com­pared to tra­di­tional meth­ods, pre­serv­ing their healthy and organolep­tic prop­er­ties.

Both crush­ing meth­ods result in a raw olive paste made of the peel of the fruit, its pulp and frag­mented pits. The paste also con­tains small olive oil drops and water, which is nat­u­rally con­tained in the olive dru­pes as they develop on the tree.

“This is one of the most del­i­cate steps in olive oil mak­ing,” Battelini said. ​“Millers have to take into account the tem­per­a­ture of the olives them­selves as they reach the mill.”

“If har­vested on warmer days, such lev­els might eas­ily exceed the 20 ºC to 22 ºC, which I con­sider the max­i­mum to obtain a high-qual­ity prod­uct,” he added.

Second step: knead­ing the olive paste

In a mod­ern mill, the freshly-pro­duced raw paste is trans­ferred into the kneader, also called a malaxer.

The kneader is a tank equipped with blades that slowly stir the paste. The stir­ring process allows the blades to break up the water-oil emul­sions cre­ated by the crush­ing.

Furthermore, the process allows larger drops of olive oil to form, eas­ing their sep­a­ra­tion from water, a cru­cial advan­tage for the final extrac­tion.

For the del­i­cate process to suc­ceed, the olive paste is gen­tly warmed. Still, the knead­ing process tem­per­a­ture will never exceed 27 ºC in meet­ing the strict require­ments for extra vir­gin olive oil.

The tem­per­a­ture is con­sid­ered the per­fect bal­ance between pro­tect­ing the best qual­i­ties of olive oil and the pro­duc­tion needs.

Kneading com­ple­tion times vary sig­nif­i­cantly depend­ing on the type of machines being used, the amount of olives, their stage of ripeness and the pro­duc­tion goals in terms of quan­tity and qual­ity. ​“The shorter the time, the bet­ter if your goal is qual­ity,” Battelini said.

Third step: olive oil extrac­tion

In tra­di­tional mills, the raw paste is not sub­jected to knead­ing. Instead, it is care­fully spread onto cir­cu­lar discs with a hole at the cen­ter.

Piles of these discs are slowly pressed together, sep­a­rat­ing the oil and water from the pulp, which remains on the discs.

Given the goals of high-qual­ity pro­duc­tion, mod­ern olive milling has adopted new means of extrac­tion, no longer based on press­ing.

Oil extrac­tion is now done with a decanter, or cen­trifuge, which spins very quickly to sep­a­rate the oil in the paste from the water and pulp. Finally, the sep­a­rated olive oil is trans­ferred from the decanter into steel con­tain­ers.

Depending on the machines’ specifics, olive oil com­ing out of the decanter might still con­tain traces of pulp, air or water.

Filtering equip­ment is often used to speed up a nat­ural process that would sep­a­rate the olive oil from those par­ti­cles, obtain­ing olive oil ready to be bot­tled and con­sumed.

How to store freshly-pro­duced olive oil

Since the domes­ti­ca­tion of the olive tree, pro­duc­ers have adopted a wide array of con­tain­ers to store their olive oil. Terracotta amphorae were used for a long time through­out the whole Mediterranean.

Nowadays, glass and more mod­ern mate­ri­als, such as fiber­glass and plas­tic, are used. Still, most extra vir­gin olive oil pro­duc­ers store their oil in stain­less steel tanks capped with inert gas, such as nitro­gen. Topping olive oil with an inert gas pre­vents oxi­da­tion.

The tanks are usu­ally kept within a tem­per­a­ture range of 14 ºC to 18 ºC to pre­serve the olive oil’s healthy and organolep­tic qual­i­ties. From there, olive oil may be bot­tled and dis­trib­uted.

Alternative extrac­tion meth­ods: the Sinolea tech­nol­ogy

An alter­na­tive olive oil extrac­tion tech­nique devel­oped at the begin­ning of the last cen­tury is known as the Sinolea pro­ce­dure, based on the sur­face ten­sion prop­er­ties of spe­cific met­als.

The goal is to sep­a­rate olive oil from the other con­tents of the paste. Metal blades are immersed in the mix, and a nat­ural adher­ing process will make the olive oil only stick to the metal.

After, the blade can be removed, and the oil it car­ries can be con­veyed to a ded­i­cated con­tainer.

In mod­ern plants, the Sinolea method starts dur­ing knead­ing, where metal blades sep­a­rate olive oil from the raw olive paste.

Milling tech­niques con­tinue to advance

Modern tech­nol­ogy has rev­o­lu­tion­ized the pro­duc­tion of high-qual­ity olive oil. Producers can quickly process large amounts of olives with advanced, elec­tron­i­cally-con­trolled milling equip­ment while pre­serv­ing their healthy and sen­sory prop­er­ties.

However, research across the olive oil-pro­duc­ing world con­tin­ues to improve qual­ity, pro­duc­tiv­ity and effi­ciency fur­ther while keep­ing sus­tain­abil­ity in mind.