WHAT IS AN OIL MILL?

the mill

As we have already been anticipating, the process of creating extra virgin olive oil cannot be understood without the figure of the oil press. For this reason, we are going to explain in detail what this term consists of, how oil mills have evolved over time, what types exist in Spain and which are the autonomous communities with a greater number. 

Origin and evolution of oil mills

The word oil mill comes from Arabic and means “place where it is squeezed”. For its part, the Royal Spanish Academy (RAE) defines the term mill as "Oil mill".

The mills have centuries of history. Juan Villar, professor at the University of Jaén and member of the Center for Advanced Studies in Olives and Olive Oil, maintains that there is research that traces the origin of the oil mills to the copper age —between the years 6000 BC and 4000 BC—.

Already at that time they managed to create a kind of stone-based machine more than two meters high, which in appearance resembled a mortar. Through its use they could grind olives and produce olive oil in small quantities. Thus, the economic emergence of these civilizations capable of producing olive oil, added to their drive to export and trade with the ports, meant that the use of this food was gradually formalized.

However, the researcher Vilar states that the first industrial mill of which there is evidence dates from around the 6th century BC, in Clazomene, a remote port city of Ancient Greece.

Those oil mills were more similar to the current ones, but they also had notable differences. In these mills there was a big screw holding the levers that exerted pressure on the olives, thus allowing the production of what is now known as extra virgin olive oil. 

The mills became so relevant in the society of the time that they even decided to place them in the central or main part of each locality, with the aim of making the distribution of olive oil easier to control and in a more visible place.

Oil mills today: distribution and operation

The evolution of the mills developed in parallel with the agricultural production capacity, that is, the more olives were cultivated, the greater the need to have more productive oil mills. 

At present, the concept of an oil mill is that of that place where the olive is processed for the production of extra virgin olive oil. 

An oil mill is made up of various areas in which the different stages or phases of the oil production process are carried out, from the collection of the olives to their storage in the cellar. Specifically, the mill usually has four different spaces: 

reception yard
It is the area through which the olives arrive after being harvested and subsequently transported. Depending on the volume of production, this place will be larger or smaller.

Generally, in the reception courtyard we will find some key elements like the hoppers —containers where the olives are deposited—, the weighers —machines where the kilos of fruit are weighed—, the conveyor belts —devices by which the olives are introduced into the mill itself—, the washers or strippers —machines that are responsible for leaving the olives perfectly clean before going to the mill— or the windmill —place where the extra virgin olive oil extraction process finally begins—. 

Oil press
Inside the mill itself, the olive paste that comes out of the mill passes through three zones: the blender —where it is kneaded—, the decanter —where the oil is extracted— and the vertical centrifuge —where any type of particle that may have remained is removed—.

After passing through these three zones, the extra virgin olive oil would be ready to go first to the decanters and finally to cellar. 

Cellar
In this area of the mill is where olive oil is stored, always with the proper classification depending on its origin and its properties. The temperature of this space and the materials with which the oil is in contact are two aspects that must be taken care of to the millimeter to achieve the preservation of its aroma and characteristics. 

This is precisely why it is so important that the cellar, as well as all the tanks that contain the oil, enjoy proper insulation due to possible temperature changes that can occur abroad. 

packaging area
Finally, so that the extra virgin olive oil can be commercialized, must transit from the deposit to the final container. Usually the package consists of bottles or carafes —glass or plastic— whose labelled It is usually added at this same stage of the process. 

Types of mills

Depending on the grinding and extraction system, oil mills can be classified or differentiated into the following types: 

Traditional
For grinding the olives use the stone: stone cones —normally granite— rotate through a system of shafts and gears on a base of the same material to obtain the crushing of the fruit. The traditional mills suppose the 14% of all oil mills registered in Spain, but they only generate the 1,16% of total production. They are currently in the phase of disappearance. 

3 phase
The grinding system is replaced by means of mechanical mills. Once the olives are crushed, the resulting mass is heated and beaten in thermomixers to facilitate the extraction of olive oil, which is subsequently carried out by means of centrifugation. As a result, virgin olive oil, dry pomace —the product made up of the dry extract of the olive— and alpechín —the mixture of the water that is used to wash the olives, as well as the water that the olives themselves have— are obtained. These mills represent the 9% of the total of our country and originate the 3,18% of total production Spanish.

2 phase
Its about most modern system and that only produces oil and alperujo —a concentrate that is made up of the different remains of the olive after having extracted the oil—. This type of mills suppose the 72% of those present in Spain and get the 90,10% of the total oil produced. 

mixed
They use two or more of the systems explained above. This type of oil mills constitutes the 5% of the total in Spain and represent the 5,55% of national production. 

In turn, depending on the type of corporate organization, in Spain the oil mills are divided into two large groups that are very even in terms of figures —according to data extracted from Monthly Report on the Market Situation of the Olive Oil and Table Olives Sector, published in December 2021—:

Cooperative mills
This oil mill model is the result of the union of several partners whose objective is to create a cooperative to grind their olives and make their own olive oil.

They currently represent a 60% of domestic production and there are a total of 907 (50,031 TP2T) registered in the country.

Industrial oil mills
Industrial-type oil mills group together industrial manufacturers Of olive oil. They may be SA —Sociedad Anónima or also known as a corporation— or SL —a limited liability company or limited partnership—.

Today produce a 40% of olive oil and in Spain there are registered a total of 906 (49,97%).

Andalusia, the leading community in number of oil mills

The olive grove encompasses 2.75 million hectares in Spain, of which 2.55 million belong to olive oil groves —93% of the total—. Likewise, our country is the world's leading exporter of olive oil, and its exports account for around 65% of its total sales. 

As the world leader in oil production, Spain has a significant number of oil mills distributed throughout the territory. According to data published in January 2022 by the Ministry of Agriculture, Fisheries and Food, there are registered a total of 1,848 mills in Spanish territory. 

As the data shows, 14 of the 17 Spanish autonomous communities have authorized oil mills, which means that they have olive trees very close to them. For your part, only 3 communities do not have oil mills officially: Asturias, Cantabria and the Canary Islands.

At the moment, Andalusia has registered a total of 865 mills, which represents 46.8% of all those present in the country. From Of these 865, 330 are located in Jaén (38,15%), 192 are in Córdoba (22,19%) and 110 in Granada (12,71%). 

In this article we have been able to learn what an oil mill is, as well as the fundamental role it plays in the production of extra virgin olive oil.