Knowing the olive oil

 This section aims to include small articles on all aspects related to virgin olive oils.
The first one is about the olive tree.


The olive tree is typical of the Mediterranean areas. It belongs to the botanic family of oleaceae, like ash trees, lilac or jasmine.


Añadir leyenda
The European Oleaceae family consists of multiple different species. More than 300 are cultivated in Spain, although not all of them have the same significance.

Cultivation of the wild olive tree (europaea var. sylvestris) started over 6,000 years ago.  The Romans spread the farming of this tree across the Mediterranean basin. In Spain, the wild olive tree is called acebuche. Smaller in size than the domesticated type, it’s more similar to a bush, and its fruit is also smaller. It grows all around the Mediterranean basin, just like holm oaks, cork oaks and mastic trees.

The most common varieties found in Spain are Picual, Hojiblanca, Cornicabra, Empeltre, Arbequina, Lechín, Picudo, Manzanilla Cacereña, Verdial, Farga, Royal, Blanqueta and Morisca. Each variety is mainly associated to a specific geographical area.

The productivity of the acebuche greatly varies. A low-productivity tree bears less than 15 kg of olives per tree or 1,500kg per hectare. A high-productivity tree bears at least 50 kg per tree or 5,000 kg per hectare.
Every year, some three million metric tons of olive oil are produced worldwide. About 40% of them are produced in Spain, with 20% of the world’s annual production concentrated in the province of Jaén.

The next main producers of olive oil in the European Union, in order of importance, are Italy, Greece and Portugal. Outside the EU, the main producers are Tunisia, Turkey and
The olive tree was considered sacred by old civilizations, as well as a symbol of peace, fertility, glory and holiness.

Chapter 2. THE OLIVE.

An olive is the fruit of an olive tree. Its form is oval, but its size varies depending on the type of tree, the variety of olive, and humidity levels – olives from irrigated groves or those grown in rainy years tend to be larger because they contain more water. 

Photo no. 1 Olive pulp and pit

Olives are a dual-purpose fruit. They can be consumed after they are cured (often with brine) and seasoned, or, more importantly, their oil can be extracted. In Spain, most olive trees (more than 90%) are intended for oil extraction.

Photo no. 2 Olive pit and seed

As depicted in photos no. 1 and 2, olives have three well-distinguished parts: an external layer, which is the skin or epicarp; a fleshy part, which is the pulp or mesocarp, that accounts for 65-85% of the fruit's weight and contains most of the oil; and a third part, which is the pit or endocarp (13-30% of the fruit’s weight). Inside the pit is a seed, as depicted in photo no. 2.


Oil usually oscillates between 15% and 25% of the fruit’s weight, and varies depending on humidity and the timing of the harvest. The remainder is water (approximately 50% of the weight), the skin, the pulp, the pit, and the seed.

The ripening of olives is a slow process. In April or May, flowers bloom on olive trees in small clusters. Most of these flowers fall off during fruition

The fruit is formed in early summer, and its colour is an intense green. In autumn, the olives are already fairly sizeable and they begin to change colour. The intense green turns into a yellowish-green and then purple shades appear. This colour change coincides with the end of the oil formation process, and this is the time to collect the fruit to obtain fresh, aromatic oil of good quality.

In December, most of the fruit is black. Its aroma is less intense, and fermentation occurs more readily because the pulp softens, the skin breaks, and hydrological process increase the acidity index (free fatty acids), causing defects in the oil’s smell and taste.

Columela (a Roman agronomist who lived in the first century) recommended harvesting the olives once they begin to change colour.
All of the photos are from my friend Carlos Peris. If you would like to reproduce them, please include the source and the author’s name. Thank you

Traducción: Luna de  Torres Carpio



At the start of Autumn, green olives begin to change colour, indicating   that the oil has already formed inside the olive and the harvest can begin.

Transportation belt. Clean olives
Nowadays, vibrating machines are usually used to take fruit off the tree, although traditional groves with trees of two or three trunks are more difficult to harvest mechanically. Cloths extended around the trunk of the tree collect the olives that fall due to movements of the vibration machine or pole. 

 The collected fruit is quickly brought to the almazara (oil mill). It is transported with maximum caution so that the olives do not deteriorate or ferment.

When olives arrive at the oil factory (almazara) the first step is cleaning the fruit: fans remove the leaves and stems that can accompany the olives. The process continues with washing the fruit, with drinking water, to take off the dust or solid residue that could have been collected with the cloths.

 The fruit is now ready to enter the hammermill, where hammers, spinning above a sieve, rotate and press the olives into a mass (in older times stone mills were used, as seen in the photo).

Mixer for the olive mass

Blades inside the mixer
Next, the olive mass passes through a mixer with slow-moving blades, which facilitate the extraction of olive oil from oil cells. 

Horizontal centrifuge or decantere
To separate the oil from the other components (skin, pit, vegetation water, and pulp residue), a horizontal centrifuge called a decanter is used, which functions like a centrifuge in a washing machine, separating the oil (low density) from the vegetative water and solid residues, collectively called alperujo


Next, the oil passes through a vertical centrifuge in order to get rid of the remaining vegetative water.

Vertical centrifuge
From here, the oil goes directly to the bodega and the consumer, although it is best to filter it (with cellulose paper) for a week before bottling it. In this way, the remaining humidity is taken out.

It is said that virgin olive oil is 100% olive juice because its extraction only involves physical processes (grinding, mixing, centrifugation) at low temperature, usually under 30ºC. The oil maintains its complete content of nutrients, vitamins, polyphenol-antioxidants, tocopherols, etc. and above all its smell and taste.

Traducción: Luna de  Torres Carpio


Many consumers have great difficulty choosing their olive oil – if only we could give them a recipe! – But it is not that easy.

In principle, it is necessary to know why there are distinct qualities, what their origin is, and how they are commercialized. It is a difficult task, and you will always have your doubts, but with great pleasure I intend to clarify them.

In chapter 3, we saw a brief overview of how to extract oil from olives: olives are pressed, mixed, and separated by centrifugation because of oil’s low density. What remains is virgin olive oil, the juice of an olive, similar to fruit juice – for example, orange juice. But, would we drink a glass of this other sort of juice? Surely not.

Olives on the Ground

Olives should be collected when they start to lose their green colour; at this optimal moment, the oil has already formed inside the fruit (in a process called lipogenesis) and it has the best aroma. However, many times farmers wait too long to collect the fruit, believing that they will get more oil if they collect them later. This is completely erroneous. Usually, winds and rain arrive and knock the fruit to the ground.
Other times, in order to reduce harvest costs, the farmers themselves throw the olives to the ground and pick them up with sweepers or ventilators (a type of vacuum). In addition to olives, they pick up dirt, rocks, and, if its rained, a large quantity of mud, as shown by the photo

When the olives are collected too late, because the farmer (erroneously) believes he will obtain more oil, the olive becomes darker and its pulp becomes softer. If flies have attacked the olives, the outcome is even worse. 

Olives collected from the tree, overripe and bitten by flies.
Soft olives ferment with ease because they bruise easily. With cracked skin and bruises, olives are likely to be infected by microorganisms, which produce hydrolytic processes and fermentations.

Olive oil from this type of fruit will be of very low quality, and may not be immediately packaged because of defects in smell and taste. If the measured defect is higher than 3.5 on a scale of 10 points, the oil is classified as “Lampante” and it is not suitable for direct consumption, according to European Union regulations.

Fermented olives
 In the past, this type of oil was called “Lampante” because, due to its low quality, it was not used for consumption but rather to illuminate lamps. That is where the name comes from.

What is “Lampante” olive oil used for today?
This oil is brought to a refinery, similar to an oil refinery but for edible oils. There, with a series of physical-chemical processes at high temperatures (almost 300 degrees Celsius), the bad smell and taste are taken out of the oil, but the majority of healthy components (polyphenols, tocopherols, vitamins, etc.) disappear as well. An inodorous, clear, and insipid oil remains. This dead oil is now named refined olive oil.
Different quality oils can be obtained depending on: the state of the olives when they arrive at the oil mill, the manner of oil production, and the preservation method
1.      Extra virgin olive oil: It is 100% juice of the best quality olive. It cannot have any defect in smell or taste and its acidity must be under 0.8%.
2.      Virgin olive oil: It is also 100% olive juice and its acidity can reach up to 2%. It can have small defects in smell and taste, less than 3.5 on a scale of 10 points.
3.      “Lampante” olive oil: It is poor quality olive oil, and is not suitable for direct consumption because it has great defects in smell and taste, higher than 3.5 points and/or the fruit does not appear and/or its acidity is higher than 2%. It must undergo the refining process in order to get rid of sensory defects and free acidity. It can be used for mixes.

Traducción: Luna de  Torres Carpio


Olive oil is not like wine, which matures with age. Virgin olive oil is the pure juice of an olive as is, without any transformative process, and therefore the earlier it is consumed, the better qualities it will have.
Oxidation is the enemy of olive oil. When olive oil comes in contact with air (oxygen), oxidation occurs. Complete oxidation results in spoiling, and a rancid smell appears.
Many factors accelerate the oxidation process, while others slow it down. It is of great interest to understand these factors, while keeping in mind that the process can be controlled but not eliminated.

Factors that speed up the oxidation process
At higher temperatures, there is greater oxidation. It is important, therefore, to keep the olive oil away from heat sources and to store it in a fresh location.
The ideal storage temperature, according to a study by L. Cerretani, is 8 degrees Celsius, and the closer the olive oil gets to that temperature, the better it is conserved.
While cooking with olive oil, we must take this factor into account, for in heating the olive oil we are triggering the oxidation process and therefore the oil's deterioration.

Olive oil, being a mono-saturated fat, takes more time to be chemically altered than poly-saturated fats (e.g. sunflower oil), because it has less free radicals.
Virgin olive oil, also a mono-saturated fat, is 100% olive juice that has not been refined, thus keeping intact its content of natural antioxidants: phenolic compounds, alpha-tocopherol, carotenoid pigments, etc. Virgin olive oil is best at withstanding non-ideal temperatures, above all when used in culinary techniques that require lots of heat, like frying and roasting.

Sunlight and diffuse light can cause the photo-oxidation of olive oil. For this reason, today most quality oils are packaged in dark glass or individual containers. Dark glass does not block all of the radiation, but does block a good portion of it. The pigments of virgin olive oil, chlorophyll and pheophytin, produce an antioxidant effect when the olive oil is in darkness, but the opposite effect when in light: light speeds up oxidation. This must be taken into account, for today consumers prefer green olive oils, but they must be kept away from light sources or they will oxidize. If you see olive oil bottles under direct light in a supermarket, you can assume the oxidation process has occurred. 
3. AIR
Any air in the bottle – either on the surface of the oil, or from multiple pours – will also trigger oxidation. For this reason, when the bottle is full, the surface area of the oil in contact with outside air is very small (only the neck of the bottle). This is calleda. However, when the bottle is almost empty, there is a lot of air and little oil, which strengthens the oxidation process.
There are many factors distinctive to specific types of olive oil that can cause oxidation.
Free acidity: Olive oil with a high percentage of free fatty acids will be more likely to oxidize.
Metallic traces, primarily copper and iron: Today, both in the oil mill and in packaging, unalterable materials are used – i.e. glass in commercially produced olive oil, and non-oxidizable steel in the bodegas of the oil mills.
Peroxides: Peroxides are formed by oxidation. At the same time, they act as catalysts, causing oxidation.

Factors that Speed Up Oxidation                                  Factors that Slow Down Oxidation
        Temperature                                                                  Mono saturated fatty acids
        Light                                                                                Phenolic compounds
        Air                                                                                    Alpha tocopherol
        Free acidity                                                                      Carotenoids
        Metallic traces                                                                   

Factors that Slow Down the Oxidation Process
High Percentage of Oleic Acid: Varieties with a high percentage of mono-saturated fatty acids (picual, cornicabra) are the most resistant to oxidation.
Virgin olive oil also has:
Some phenolic compounds: Polyphenols are the most important antioxidants
A large quantity of alpha-tocopherol reduces oxidation.
Carotenoids: These pigments also reduce oxidation.
When olive oil starts to oxidize, it progressively loses its positive attributes (fruitiness, bitterness, spiciness), and then an old, rancid smell appears. ´
In summation:
The time it takes for olive oil to change, to become rancid, depends on its initial state (acidity, presence of peroxides, percentage of oleic acids, carotenoids) and also the manner in which it is stored, avoiding the factors that accelerate oxidation the most: temperature, light and air.
Traducción: Luna de  Torres Carpio

2 comentarios:

  1. Gracias por tan estupendo aporte para la difusión y el conocimiento de la cultura del aove fuera de nuestras fronteras. He disfrutado mucho leyéndolo. Es un resumen magistral de lo que es necesario conocer. Felicidades!

  2. Millón de gracias!. Es un lujo contar con unos lectores tan agradecidos. Tengo muchos temas todavía pendientes. Vuestros comentarios, me ayudan a continuar.
    Un saludo.


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