Olive oil extraction is the process of extracting the oil present in olive

drupe In botany, a drupe (or stone fruit) is an indehiscent fruit in which an outer fleshy part ( exocarp, or skin, and mesocarp, or flesh) surrounds a single shell (the ''pit'', ''stone'', or ''pyrena'') of hardened endocarp with a seed (''kernel ...

s, known as

olive oil Olive oil is a liquid fat obtained from olives (the fruit of ''Olea europaea''; family Oleaceae), a traditional tree crop of the Mediterranean Basin, produced by pressing whole olives and extracting the oil. It is commonly used in cooking: ...

. Olive oil is produced in the mesocarp

cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...

, and stored in a particular type of

vacuole A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic m ...

called a lipo vacuole, i.e., every cell contains a tiny olive oil droplet. Olive oil extraction is the process of separating the oil from the other fruit contents (vegetative extract liquid and solid material). It is possible to attain this separation by physical means alone, i.e., oil and water do not mix, so they are relatively easy to separate. This contrasts with other

oils An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturate ...

that are extracted with chemical

solvents A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

, generally

hexane Hexane () is an organic compound, a straight-chain alkane with six carbon atoms and has the molecular formula C6H14. It is a colorless liquid, odorless when pure, and with boiling points approximately . It is widely used as a cheap, relative ...

. The first operation when extracting olive oil is washing the olives, to reduce the presence of

contaminant Contamination is the presence of a constituent, impurity, or some other undesirable element that spoils, corrupts, infects, makes unfit, or makes inferior a material, physical body, natural environment, workplace, etc. Types of contamination Wi ...

s, especially

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...

which can create a particular flavor effect called "soil taste".

Olive presses

Ancient olive oil extractor-juicer, Dion (reconstruction)

People have used olive presses since Greeks first began pressing olives over 5,000 years ago. Roman olive presses survive to the present time, with a notable collection present at Volubilis in

Morocco Morocco (),, ) officially the Kingdom of Morocco, is the westernmost country in the Maghreb region of North Africa. It overlooks the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to A ...

. An olive press works by applying pressure to olive paste to separate the liquid oil and vegetation water from the solid material. The oil and vegetation water are then separated by standard

decantation Decantation is a process for the separation of mixtures of immiscible liquids or of a liquid and a solid mixture such as a suspension. The layer closer to the top of the container—the less dense of the two liquids, or the liquid from which t ...

. Olive presses were traditionally built within walled structures. Traditional olive-presses consisted of a large, cylindrical millstone mounted by an upper milling-stone used to grind the olives and their pits into a pulp."The lower millstone, etc." Translation here follows the interpretation of the Hebrew words = ''yam'', and = ''memal'', as explained by Mishnaic exegetes

Hai Gaon Hai ben Sherira (Hebrew: האי/י בר שרירא) better known as Hai Gaon (Hebrew: האי/י גאון, חאיי גאון), was a medieval Jewish theologian, rabbi and scholar who served as Gaon of the Talmudic academy of Pumbedita during the ...

(939–1038) on Mishnah (''Taharot'' 10:8);

Maimonides Musa ibn Maimon (1138–1204), commonly known as Maimonides (); la, Moses Maimonides and also referred to by the acronym Rambam ( he, רמב״ם), was a Sephardic Jewish philosopher who became one of the most prolific and influential Torah ...

Mishnah The Mishnah or the Mishna (; he, מִשְׁנָה, "study by repetition", from the verb ''shanah'' , or "to study and review", also "secondary") is the first major written collection of the Jewish oral traditions which is known as the Oral Tor ...

''Baba Bathra'' 4:5 and in his '' Mishne Torah'' (Hil. ''Mekhirah'' 25:7) as pointed out by Rabbi Vidal of Tolosa; and by

Nathan ben Jehiel Nathan ben Jehiel of Rome (Hebrew: נתן בן יחיאל מרומי; ''Nathan ben Y'ḥiel Mi Romi'' according to Sephardic pronunciation) ( 1035 – 1106) was a Jewish Italian lexicographer. He authored the Arukh, a notable dictionary of Talmu ...

(1035–1106) in his ''Sefer ha-Arukh'', s.v. ;

Obadiah Bartenura Obadiah ben Abraham of Bertinoro ( he, ר׳ עוֹבַדְיָה בֵּן אַבְרָהָם מִבַּרְטֵנוּרָא; 1445 – 1515), commonly known as "The Bartenura", was a 15th-century Italian rabbi best known for his popular comme ...

in his commentary on

(''

Maaserot Ma'aserot ( he, מַעֲשְׂרוֹת, lit. "Tithes") is the seventh tractate of ''Seder Zeraim'' ("Order of Seeds") of the ''Mishnah'', '' Tosefta'', and the ''Jerusalem Talmud''. It discusses the types of produce liable for tithing as well as ...

'' 1:7), as well as by

Moses Margolies Moses Margolies or Moshe ben Shimon Margalit ( he, משה מרגלית; c. 1715 in Kėdainiai, Lithuania – 1781 in Brody, then a private town of the Polish Crown) was a Lithuanian Jewish rabbi and a commentator on the Jerusalem Talmud. Works M ...

(1715–1781) in his commentary ''P'nei Moshe'' on the

Jerusalem Talmud The Jerusalem Talmud ( he, תַּלְמוּד יְרוּשַׁלְמִי, translit=Talmud Yerushalmi, often for short), also known as the Palestinian Talmud or Talmud of the Land of Israel, is a collection of rabbinic notes on the second-century ...

(''Baba Bathra'' 4:5), and by Nissim of Gerona on Rav Alfasi's commentary on ''Avodah Zarah'' 75a, among others. See also , s.v. Formerly, the upper milling-stone was turned by a beast of burden pulling a wooden beam attached to the stone. After which, the pulp was collected and kneaded. It was then placed within frails (being no more than flexible, woven baskets made of thick fibrous material, usually of rushes, palm fronds,

hemp Hemp, or industrial hemp, is a botanical class of '' Cannabis sativa'' cultivars grown specifically for industrial or medicinal use. It can be used to make a wide range of products. Along with bamboo, hemp is among the fastest growing plants ...

or willow splints), stacked one on top of the other, to which was applied a stone weight to release the oil from the pulp. The extracted liquid which is obtained consists of oil and vegetable water (''

amurca Amurca is the bitter-tasting, dark-colored, watery sediment that settles out of unfiltered olive oil over time. It is also known as "olive oil lees" in English. Historically, amurca was used for numerous purposes, as first described by Cato the E ...

'') mixed together, and runs off into a pit. After settling, the oil rises to the surface and is removed by way of decantation. Filtering the oil produces a clearer batch of oil. The olive residue that remained was used for lighting fires. This basic method is still widely used today, and it is still a valid way of producing high quality olive oil if adequate precautions are taken. First the olives are ground into an olive paste using large

millstone Millstones or mill stones are stones used in gristmills, for grinding wheat or other grains. They are sometimes referred to as grindstones or grinding stones. Millstones come in pairs: a wikt:convex, convex stationary base known as the ''be ...

s at a corporate oil mill. The olive paste generally stays under the stones for 30–40 minutes. This has three objectives: * Ensure that olives are well ground * Allow enough time for the olive drops to join to form the largest droplets of oil * Allow the fruit

enzymes Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. ...

to produce some of the oil aromas and taste Olive oil mills very rarely use a modern crushing method with a traditional press. In modern-day mills, after grinding, the olive paste is spread on fibre discs, which are stacked on top of each other, then placed into the mechanical press. In modern times, these discs are made of synthetic fibres which are easier to clean and maintain. These discs are then put on a hydraulic piston, forming a pile. Pressure is applied on the disks, thus compacting the solid phase of the olive paste and percolating the liquid phases (oil and vegetation water). The applied hydraulic pressure can go to 400 atm. To facilitate separation of the liquid phases, water is run down the sides of the discs to increase the speed of percolation. The liquids are then separated either by a standard process of decantation or by means of a faster vertical

centrifuge A centrifuge is a device that uses centrifugal force to separate various components of a fluid. This is achieved by spinning the fluid at high speed within a container, thereby separating fluids of different densities (e.g. cream from milk) or ...

. The traditional method is a valid form of producing high-quality olive oil, if after each extraction the discs are properly cleaned from the remains of paste; if not the leftover paste will begin to ferment, thereby producing inconsistencies of flavors (called defects) that will contaminate the subsequently produced olive oil. A similar problem can affect the grindstones that, in order to assure perfect quality, also require cleaning after each usage.

Grades of olive oil

In ancient Palestine and the

Levant The Levant () is an approximate historical geographical term referring to a large area in the Eastern Mediterranean region of Western Asia. In its narrowest sense, which is in use today in archaeology and other cultural contexts, it is ...

, three methods were used to produce different grades of olive oil. The finest oil was produced from fully developed and ripe olives harvested solely from the apex of the tree, and lightly pressed, "for what flows from light pressure is very sweet and very thin.", pp
288–289
/ref> The remaining olives are pressed with a heavier weight, and vary in ripeness. Inferior oil is produced from unripe olives that are stored for extended periods of time until they grow soft or begin to shrivel to become more fit for grinding. Others are left for extended periods in pits in the ground to induce sweating and decay before they are ground. According to the ''Geoponica'', salt and a little nitre are added when oil is stored.

Advantages and disadvantages

Proper cleaning produces higher-quality oil. Grindstones, while ancient in design, are a suitable way to grind olives, because this method breaks up the

's pulp while only slightly touching the nut and the skin. This reduces the release of the oil

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...

enzymes present in these organs. In addition, in this extraction method, the introduction of water is minimal when compared to the modern one, thus reducing the washing-off of the

polyphenol Polyphenols () are a large family of naturally occurring organic compounds characterized by multiples of phenol units. They are abundant in plants and structurally diverse. Polyphenols include flavonoids, tannic acid, and ellagitannin, some ...

s. The exhausted paste, called

pomace Pomace ( ), or marc (; from French ''marc'' ), is the solid remains of grapes, olives, or other fruit after pressing for juice or oil. It contains the skins, pulp, seeds, and stems of the fruit. Grape pomace has traditionally been used to pro ...

, has a low content of water, making it an easier residue to manage. Advantages * Better grinding of the olives, reducing the release of oil

enzymes * Reduced added water, minimizing the washing of polyphenols * Pomace with a low content of water easier to manage Disadvantages * Difficult to clean * Non-continuous process with waiting periods thus exposes the olive paste to

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

and light * Requires more manual labor * Longer production time from harvest to pressing

Decanter centrifugation

The modern method of olive oil extraction uses an industrial decanter to separate all the phases by

centrifugation Centrifugation is a mechanical process which involves the use of the centrifugal force to separate particles from a solution according to their size, shape, density, medium viscosity and rotor speed. The denser components of the mixture migrate ...

. In this method the olives are crushed to a fine paste. This can be done by a hammer crusher, disc crusher, depitting machine or knife crusher. This paste is then malaxed for 30 to 60 minutes in order to allow the small olive droplets to agglomerate. The aromas are created in these two steps through the action of fruit

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

s. Afterwards the paste is pumped into an industrial decanter where the phases will be separated. Water is added to facilitate the extraction process with the paste. The decanter is a large capacity horizontal

rotating approximately 3,000 rpm, the high

centrifugal force In Newtonian mechanics, the centrifugal force is an inertial force (also called a "fictitious" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It is directed away from an axis which is paralle ...

created allows the phases to be readily separated according to their different densities (solids > vegetation water > oil). Inside the decanter's rotating conical drum there is a coil that rotates more slowly, pushing the solid materials out of the system. The separated oil and vegetation water are then rerun through a vertical centrifuge, working around 6,000 rpm that will separate the small quantity of vegetation water still contained in oil and vice versa.

Three, two, and two and a half phases decanters

With the three phases oil decanter, a portion of the oil polyphenols is washed out due to the higher quantity of added water (when compared to the traditional method), producing a larger quantity of vegetation water that needs to be processed. The two phases oil decanter was created as an attempt to solve these problems. Sacrificing part of its extraction capability, it uses less added water thus reducing the phenol washing. The olive paste is separated into two phases: oil and wet pomace. This type of decanter, instead of having three exits (oil, water, and solids), has only two. The water is expelled by the decanter coil together with the pomace, resulting in a wetter pomace that is much harder to process industrially. Many pomace oil extraction facilities refuse to work with these materials because the energy costs of drying the pomace for the hexane oil extraction often make the extraction process sub-economical. In practice, then, the two phases decanter solves the phenol washing problem but increases the residue management problem. This residue management problem has been reduced by the collection of this wetter pomace and being transported to specialized facilities called extractors which heat the pomace between 45 °C and 50 °C and can extract up to a further 2 litres per 100 kilos of pomace using adapted two-phase decanters. The two-and-a-half-phase oil decanter is a compromise between the two previous types of decanters. It separates the olive paste into the standard three phases, but has a smaller need for added water and also a smaller vegetation water output. Therefore, the water content of the obtained pomace comes very close to that of the standard three-phase decanter, and the vegetation water output is relatively small, minimizing the residue management issues. Depending on the olives and processing, the

Decanter A decanter is a vessel that is used to hold the decantation of a liquid (such as wine) which may contain sediment. Decanters, which have a varied shape and design, have been traditionally made from glass or crystal. Their volume is usually equ ...

or Tricanter can extract between 85 and 90% of the olive oil in the 1st extraction. The yield from olive oil manufacture can be increased even further with a 2nd extraction. The olive oil yield increases to as much as 96% by combining the 1st and 2nd extractions.

Advantages and disadvantages

Advantages * Compact machinery: only one decanter required * Continuous and automated * Limited labor required * Highest percent of oil extraction * Vegetable water disposal less of a problem * Olive oil from two-phase centrifugation systems contains more phenols,

tocopherol Tocopherols (; TCP) are a class of organic chemical compounds (more precisely, various methylated phenols), many of which have vitamin E activity. Because the vitamin activity was first identified in 1936 from a dietary fertility factor in rat ...

s, trans‑2‑hexenal, and total aroma compounds and is more resistant to oxidation than oil from three-phase ones and from hydraulic presses Disadvantages * Expensive * More technical labor required * High energy consumption * Pomace may end up moist * Greater amount of vegetable water to be disposed of * Reduced antioxidants due to added water * Subject to wear from rocks, grit

Sinolea method

The Sinolea method to extract oil from the olives was introduced in 1972; in this process, rows of metal discs or plates are dipped into the paste; the oil preferentially wets and sticks to the metal and is removed with scrapers in a continuous process. It is based on the different

surface tension Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) t ...

of the vegetation water and the oil, these different physical behaviors allow the olive oil to adhere to a steel plaque while the other two phases remain behind. Sinolea works by continuously introducing several hundreds of steel plaques into the paste thus extracting the olive oil. This process is not completely efficient leaving a large quantity of oil still in the paste, so the remaining paste has to be processed by the standard modern method (industrial decanter).

Advantages and disadvantages

Advantages * Higher polyphenol content of oil * Low temperature method * Automated * Low labor * Oil/water separation step is not needed * Low energy requirement Disadvantages * Often must be combined with one of the above methods in order to maximize oil extraction which requires more space and labor * Large surface areas can lead to rapid

of the olive product * Sale of future machines currently outlawed in the

European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are located primarily in Europe, Europe. The union has a total area of ...

due to difficulty in cleaning large surface areas

First cold pressed – cold extraction

Many oils are marketed as first cold pressed or cold extraction. "Cold" means no heat is added during extraction. "Pressed" means that the olives are crushed in a mill to extract the oil. In the EU, these designations are regulated by Article 5 o
Commission Regulation (EC) No 1019/2002 of 13 June 2002 on marketing standards for olive oil
This article states that in order to use these designations the olive oil bottler must prove that the temperature of malaxation and extraction was under 27 °C (80 °F). For olive oil bottled outside EU countries, this regulation does not apply, and thus the consumer has no assurance that these statements are true. The temperature of malaxation and extraction is crucial due to its effect on olive oil quality. When high temperatures are applied, the more volatile aromas are lost and the rate of oil oxidation is increased, producing therefore lower quality oils. In addition, the chemical content of the polyphenols,

antioxidants Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. This can lead to polymerization and other chain reactions. They are frequently added to industrial products, such as fuels and lubricants, ...

, and

vitamin A vitamin is an organic molecule (or a set of molecules closely related chemically, i.e. vitamers) that is an essential micronutrient that an organism needs in small quantities for the proper functioning of its metabolism. Essential nutrie ...

s present in the oil is reduced by higher temperatures. The temperature is adjusted basically by controlling the temperature of the water added during these two steps. High temperatures are used to increase the yield of olive oil obtained from the paste.

Alternative configurations

Some producers, in order to maximise product quality, choose to combine the traditional grinding method, the stone mill, with a modern

decanter A decanter is a vessel that is used to hold the decantation of a liquid (such as wine) which may contain sediment. Decanters, which have a varied shape and design, have been traditionally made from glass or crystal. Their volume is usually equ ...

. This technique produces more selective grinding of the olives, reduces the malaxation time olive paste, and avoids the complicated cleaning of the olive press fibre disks. Because the use of the stone mill requires a loading and unloading phase, this extraction method is discontinuous, i.e., there are times when all the machinery is stopped, therefore it is generally not used on a large commercial scale, being applied only by small scale olive mills producing high quality olive oil.

Consumer point of view

High quality olive oil can be obtained by all the methods if proper measures are taken. Olive oil quality is equally dependent on the quality of the olives themselves and on the time they have to wait from harvesting to extraction, in addition to the extraction method itself. The two main agents that cause the degradation of olive oil are oxygen and light. Once an olive is harvested, it should be pressed within 24 hours. Oxidation begins immediately upon harvesting. In the period between harvest and grinding, the fruits' enzymes are very active and increasingly degrade the

endogenous Endogenous substances and processes are those that originate from within a living system such as an organism, tissue, or cell. In contrast, exogenous substances and processes are those that originate from outside of an organism. For example, ...

oil, and therefore oil obtained after a longer wait is of lower quality, presenting higher

acidity In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a ...

(

free fatty acids In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, f ...

percentage). In addition, if additional oxygen is allowed to interact with the olive paste during the extraction process, the acidity level will increase further. Sealed extraction methods are best to prevent the continued introduction of oxygen, as well as light to the oil. After extraction is complete, in most cases

unfiltered olive oil Unfiltered olive oil (also known as ''cloudy olive oil'', ''veiled olive oil'', or ''olio nuovo'') is an intermediate product of olive oil extraction. It is actually the initial cloudy juice of the olive drupes soon after crushing, separation and ...

appears somewhat cloudy, mainly due to the presence of minute amounts of water and suspended solids of olive pulp and seed. This type of oil is therefore sometimes called ''cloudy'' or ''veiled olive oil''. It is common practice that unfiltered olive oils are then "racked" for a time, i.e. stored in cool

stainless steel Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's r ...

silos with a conical bottom that are pumped free of oxygen to enable the precipitation and separation of the two phases and facilitate later

filtration Filtration is a physical separation process that separates solid matter and fluid from a mixture using a ''filter medium'' that has a complex structure through which only the fluid can pass. Solid particles that cannot pass through the filter ...

; it will also contribute in the integrity and stability of the oil.

Future prospects

The future of olive extraction points to reducing the negative aspects of the present methods, decreasing the degradation oil produced by the extraction process in itself. * Reducing the oxidation by performing part of the process of malaxation and the extraction under a controlled

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

atmosphere * Extracting the nut of the olive before grinding, this will reduce the release of oxidative enzymes present in this organ, and yield a

that is free from wood residues, making it possible to be used in animal feeding * Reducing the addition of water to minimize the washing of polyphenols * Improving the Sinolea method, through an increase in the efficiency of the

adsorption Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a ...

of the oil to the plates, thus reducing the need for the use of standard methods of extraction

Notes

References

Bibliography

* “Polyphenols in olive oils”. T. Gutfinger, ''Journal of the American Oil Chemists' Society'', Volume 58, Number 11, 966–968,

External links

Commission Regulation (EC) No 1019/2002 of 13 June 2002 on marketing standards for olive oil

Putting crushed olives into basket-containers for pressing
(ca. 1920 and 1933),

Library of Congress The Library of Congress (LOC) is the research library that officially serves the United States Congress and is the ''de facto'' national library of the United States. It is the oldest federal cultural institution in the country. The libra ...

Olive crushing and pressing
(ca. 1920 and 1933),

{{olives Food industry Industrial processes Olive oil nl:Olijfolie