From field to table > Growing and Processing

Extra Virgin: from the tree to the table

Extra Virgin: from the tree to the table

A large part of the population in Mediterranean countries is familiar with the term or concept "virgin olive oil" and closely relates it to their diet, but unfortunately, due to a lack of necessary information, most do not ascertain the real meaning of all that is represented by these words. They are not actually aware of things like what products are used, how they are produced, what differences exist between them, what features should be assessed, how and where to use the products, and how important they can be in their diet, and, as an immediate consequence, their health.

The causes behind this situation are complex, involving multiple factors, of which we should highlight the lack of importance of nutrition in education, the lack of interest in maintaining the food culture of these countries, and the minimum information offered by sector producers to consumers.

It seems logical to begin by pointing out that olive oil is virgin olive oil juice, properly separated from the other components of this fruit. Therefore, it is necessary to emphasize its character, fundamentally, as a natural juice, as its own Arabic root "az-zeit " states, translating as olive juice.

As in all natural juices, the processing or extraction system can only use mechanical or physical means to extract and retain the characteristics of the constituents of the juice, in a similar manner as is done with fruits.

This peculiarity in elaboration is what gives olive juice its character as natural or virgin. Therefore, all the oil obtained from olives, at any stage, by these means, is called virgin.

However, when you use olives with optimal ripening stages, freshly picked, of good quality, without defects or alterations, and the adequate systems and appropriate processing conditions are employed, then olive oil possesses exceptional characteristics of appearance, fragrance and flavor, making it unique among vegetable oils. It can be consumed directly, raw, retaining virtually full vitamin and antioxidant content, essential fatty acids, and many other natural products of dietary substance. Or, thanks to these high quality properties, when used with other foods it will significantly improve the resulting ensemble regarding aromas, flavor, appearance, swallowing, and nutrition.

Unfortunately, all of the virgin olive oil that is produced does not meet the above-mentioned conditions and characteristics, so there are oils with a certain degree of deterioration, significantly affecting the quality, under the criteria of composition and organoleptic and nutritional characteristics.

Experience shows that the deterioration and lack of quality in oil typically occurs as a result of defective fruit handling and the inadequate use of processing systems, because, while it is true that the different existing varieties of olives will produce oils of different characteristics under optimum conditions, none of them will produce genetically defective oil. Only fruits that have been attacked by pests and diseases, that have suffered adverse weather conditions, or have fallen to the ground before harvesting, produce inevitably altered oil. The remaining production of defective virgin olive oil is the result of untimely collection, of prolonged and improper storage of fruits, of defective processing conditions, and incorrect classification and storage of the oil.
Understandably, the defective or damaged virgin oils, called "lampante" or refinable, are not directly suitable for consumption, mainly for their unpleasant organoleptic characteristics and the altering of certain components.

In order to use these oils as food, it is necessary to eliminate the detected defects, through refining, which should more correctly be named "rectification". Oils processed in this way are usually odorless and tasteless and, to improve their organoleptic quality, they are mixed with certain amounts of virgin oil, creating a new ensemble, called olive oil.
The process of oil formation or, more correctly, lipid synthesis, is effected by a sequence of biochemical processes that usually begins during development of the olives, approximately in the hardening period of the endocarp. In a first stage, the saturated fat chain is formed, which in successive steps is elongated and desaturated in order to provide the full range of fatty acids, saturated and unsaturated, necessary in the functioning of living organisms.

This oil formation process usually reaches its maximum when the olives are in a state of maturation called "envero", a moment when most of the fruits present a changing color (yellow-green- violet-lightly blackish).


Optimal harvest time

The most appropriate way to determine when the olives are at their peak of ripeness is by analytical observation of the total oil content with reference to dry matter, the degree of extractability, and the quality, about a month before the start of the harvest.

Once we know the evolution and the time of maximum quality and quantity, we proceed to perform the collection, without ever forgetting that quality fruits are collected avoiding, as far as possible, damage to plant integrity or mixing with other, lower quality fruit.

The collection process is one of the most expensive activities in olive growing and also a point where you can start to deteriorate the quality of the oil with the use of inadequate criteria.

At present, in Spain, the most widely used harvest methods are vareo (or handpole-beating) or the mechanized vibration of branches and trunks, the latter being adapted at a rapid pace, especially in large and new plantations.

Essentially, the collection systems for olives coming down from the trees as a result of the aforementioned equipment are the main cause in the incorporation of impurities such as leaves, branches, earth and stones, which must be removed to provide adequate elaboration.

During harvest, the olives are separated according to their variety and quality and are transported to the mill either in suitable containers to prevent spoilage, or in bulk, on trailers.

The oil mill or factory

The mill is the factory that performs the set of processes that constitute the development of virgin olive oil, and it has four basic areas:
In the first, called the reception area, commonly known as "patio", is where the entry tasks are performed: identification and classification of the fruit depending on the characteristics of the olives, and the removal of impurities with cleaning systems using vibration and air to eliminate the leaves, stems and soil that come with the olives. Heavier impurities such as stones, metals, etc., are separated in a washing machine by means of a stream of water in closed circuit.


From this point there is a weight control of the lots, and a representative sample is taken for lab testing, in order to control and assess the oil content and quality.

The lots of olives that share similar characteristics are stored in large surge bins to wait before entering the manufacturing area.

The second area is called the elaboration, manufacturing or machinery unit. It holds the elaboration system of the facility. As stated above, to maintain the characteristics of a fruit juice, only mechanical or physical means can be used and, so far, the only oil methods known to the oil sector for solid-liquid separation are the effects of pressure, supplied by the hydraulic press, and the effect of centrifugation, provided by a horizontal centrifuge decanter, commonly known in Spanish as a decanter.

The elaboration method, either by pressure or by centrifugation, consists of a series of processes that begin with preparation of the paste or batter.

Most of the oil in the olive is found in the vacuoles of the mesocarp parenchyma cells. To bring this oil out it is necessary to break the cell structure of the olive. For this purpose, mills use stone or metal grinders that grind the fruit entirely. In present day, although it is still uncommon, there are facilities that perform deboning of the olive to obtain olive oil with milder organoleptic characteristics, since there is an absence of interactions with certain components of the seed of the bone during processing.

The ground paste holds a given degree of oil droplets that are dispersed and emulsified and must be collected by means of coalescence, forming larger volume droplets and, if possible, a continuous oil phase overlying the paste. This initial separation effect is performed in a process called thermo-mixing, whose mission is to provide a slow kneading of the paste. This operation is carried out in vertical or horizontal, cylindrical or semi-cylindrical containers, holding a bladed shaft in the interior and surrounded by a heating chamber on the exterior.

The paste, shifted in the interior of the mixers by the effect of the slow movement of the blades (18-20 rpm), together with mild heating (25-30 ° C) and the time of permanence (60-90 min.), changes its rheology, transforms its aspect in proportion to the degree of separation of the oil, and facilitates its extraction.

Next, the paste is subjected to solid-liquid separation, which is the process that most notably sets the difference between the press system and centrifugation. Reproduced below is the flow chart of the different processing systems.

Click on image to preview

Next, the paste is subjected to solid-liquid separation, which is the process that most notably sets the difference between the press system and centrifugation. Reproduced below is the flow chart of the different processing systems.

There are currently approximately 1,750 mills in Spain, of which about 0.5% use a press system, and the rest uses centrifugation. The most notable differences in the latter system are that the processing is performed continuously, has more processing capacity, solid-liquid separation is performed in a short period of time with better performance, and it is generally easier and cheaper to obtain quality oil.

The centrifuge system, first used in Spain in the early 70's, is called three-phase or three-output because it performs three independent separations: oil, pomace, and alpechín, or vegetable water. Pomace is the solid phase which occurs in the solid-liquid separation and is formed by fractions of the endocarp, exocarp and mesocarp of the olive and certain percentages of oil and vegetable water, due to the impossibility of completely removing the liquid phase using mechanical methods.

Pomace, due to its high production and to the residual oil it contains, is considered as a byproduct of particular industrial interest, both for its oil content and the energy content in its biomass.

Another component, alpechín, is the aqueous phase of the solid-liquid separation. It consists mainly of much of the vegetable water in olives, plus the fluidization water used in the decanter. Because of the organic components of the vegetable water, it has a high organic load that makes it a liquid contaminant, so it is not allowed to discharge it into public waterways.

The fact that the system of three-phase centrifugation produces about 1.3 liters of vegetable water per kilogram of olives caused decanter technology to be modified in the early 90's, to eliminate the requirement for the addition of virtually any fluidization water and, what is more, to eliminate the output for the aqueous phase. Therefore, this decanter has only two outputs, one for oil and one for the solids, which includes the vegetable water. It is called a two-phase or two-output decanter.

Currently, in Spain, about 98% of the mills use two-phase centrifugation, and 2% use three-phase.

The oil produced in the three or two-phase decanters is usually accompanied by a small percentage of solid and liquid impurities, so it has to be subjected to a cleaning or purification process. This operation is normally carried out by means of liquid -liquid centrifuge, using the vertical centrifugal separator with conical plates and a rotation speed of approximately 6,500 rpm.

The oil from the decanter is introduced in this machine with a water flow rate of approximately 35% and a temperature of 25-35 ° C, serving as purifying element. The result is a cleaner oil, substantially free from impurities, and a washing water flow containing almost all of these impurities. This resulting liquid therefore has a determined polluting power, depending on the type of decanter (three or two outputs) and the degree of separation efficiency.

In recent years, by minimizing the added water consumption, heating energy, volume and pollution of oil washing, the cost and maintenance of the machine, and power consumption, some manufacturers have seen fit to use only the decanter for the purification of the oil. For this operation, conical bottom, high capacity metal decanters were designed, where oil is deposited so that a relation of time and gravity will remove the highest percentage of impurities.

Unfortunately, this system makes the separation of impurities much slower, so the impurities stay in contact with the oil longer, which ultimately deteriorates their good organoleptic characteristics. Therefore, it is reasonable to question whatever the degree of economic savings and reduction of water pollutants, since, in order to achieve a lower interference of the oil with impurities, it is necessary to maintain a good interior cleaning of the decanters, and all at the expense in the quality of the oil.

To partially offset the effects that negatively affect the quality of the oil and certain impacts affecting the environment, olive oil makers have begun using a new centrifuge system without added water, which eliminates or drastically reduces pollutant wash water, eliminates impurities almost instantly, preserves the antioxidant compounds, and maintains the sensory characteristics of the oil.

Given the situation of these purification procedures, which is necessarily and primarily related to the quality of the oil, the mills can decide what should be installed according to the oil they wish to produce.

The oil obtained from the output of any of the above processes has a cloudy aspect, as do all freshly obtained fruit juices, often due to its composition and the small percentage of residual moisture. This authentic olive oil juice is called newly produced virgin olive oil.

In order for the oil being produced continuously to constitute a defined and homogeneous lot, to eliminate the air entrapped in centrifugation, and to decant the small proportion of impurities which it still possesses, it then passes through what are called pre-cellar deposits, where it remains for a period of 24-48 hours with programmed purges to remove decanted impurities.

From this period of time, expert personnel must conduct a sampling to assess the quality and make the initial classification of the lot. This assessment is often carried on the basis of acidity and organoleptic characteristics under the criteria of production.

Once the quality of the lot is assessed, the oil is transferred to the appropriate deposit, which has previously been differentiated in order to separate different qualities within the cellar, where the oil will remain until its commercialization.

A good conservation in the cellar

The mill's cellar is the third structural zone. It is usually independent of the areas described earlier and meets a number of requirements, such as thermal insulation, temperature control, artificial lighting, non-absorbent walls and floors, with easy hygiene, etc.. It holds, in an orderly disposition, a series of deposits depending on the level of production. The most widespread type of deposit is usually cylindrical and constructed with inert materials (epoxy resin coated steel, polyester and fiberglass or stainless steel), while the most representative unit capacity in mills of medium and high production is 50 tons.

Normally, the group of deposits held in the cellar is divided into groups according to different categories of the oil obtained, in order to thoroughly carry out the classification of production.
The main factors that cause spoilage and deterioration of the oil are oxygen from air, light, heat, organic matter waste from processing and time, all of which are minimized as far as possible.

The current trend in mills that produce high quality oils is to have tanks with nitrogen inerting in order to prevent contact with atmospheric oxygen during storage.

As can be deduced from all that has been stated, olives allow us to obtain different olive oil types in accordance with the quality of the product of origin. The designation of oils is regulated by a number of analytical determinations contained in EU Regulations which are constantly updated.

Therefore, quality virgin olive oil depends on the goodness of the fruits, on the good practices of the elaboration processes, on a correct classification of the oil and an adequate storage and preservation.

A minority consumes extra virgin olive oil

According to data from the Spanish Ministry of Agriculture, Food and Environment (MAGRAMA), the average oil consumption in Spain in the period between June 2012 and May 2013 was 12.8 liters per person per year, of which olive oil was 5.25 liters (41.02%), virgin olive oil, 3.69 liters (28.83%), sunflower oil, 3.45 liters (26.95%) and olive pomace oil, 0.41 liters (3.20%).

It is certainly surprising that in Spain, the world's largest producer, the "olive oil" category is the most consumed. Such a circumstance highlights the lack of knowledge regarding the sensory characteristics of virgin oils and also its enormous potential for use in the national cuisine.

The sector producing virgin olive oil sold approximately 92% of the bulk production, eminently to bottling companies and refineries, and the rest goes to the bottled oil.

Presently, there is an increasing number of mills or mill associations that market their oil in bottled formats. In these cases, the mill is equipped with a fourth space, the bottling area, dedicated to this function.

Bottled oil is usually filtered for the market. It was already mentioned that newly produced virgin oil is cloudy and has a suspension of a small percentage of impurities that reduce their concentration during decanting and storage, but can hardly be entirely removed, especially in early season oils, which are usually the highest quality. Due to this, when bottled oil is unfiltered and consumption does not take place within a reasonable time period, it may show small dark-colored decantations that can cause a bad impression, especially if the consumer does not know of these peculiarities. To avoid this situation, virgin oil undergoes a filtration process that is usually carried out by adding filtering earth, usually from natural materials such as diatomaceous earth and cellulose, which have a high absorption capacity due to their high surface area and porosity, whose mission is to retain solid particles and remove excess moisture.

The combination of oil and filtering earth is passed through a filter with plates or paper cartridge that will retain the solids and make the oil clean and bright.

The filtered oil then goes on to a storage tank, which then can be the mother that feeds the bottling plant.

In practice, most of the bottling companies run continuously and include systems for variable dosage volume, according to the container in use. High-capacity bottlers feature automatic positioning of containers, dispensing, labeling, capping, boxing, sealing and palletizing.

The types and volumes of containers are usually used depending on the category of oil to be bottled, demanding containers that will not change shape for the higher classes, impermeable to oil and gas, resistant, offering a good appearance, and endowing the content with class. Normally, virgin and extra virgin olive oils employ glass and tin. For extra virgin, the usual volumes are 0.5 and 0.75 l. and for virgin, volumes exceeding one liter; containers such as tetrabrik are still scarce for this category of oils.

The remaining categories of oil are usually bottled in PET, typically in volume of 1 l. This packaging offers good performance and a good value as a container for oils.

The Spanish oil consumer likes a transparent container offering an adequate view of the color and transparency of the oil. There tends to be little taste for the green or yellowish green oils coming out early in the campaign - which are typically the highest-quality. This circumstance is the product of a general lack of information and a familiarity with other types of oil, and likewise, the average consumer does not adequately assess the organoleptic characteristics of quality oils which, in most cases, will be unfamiliar.

As inhabitants of the world's largest producing country of olive oil, and given the ease with which this range of high quality products is readily available, it makes sense to develop and transmit the culture of olive oil in general, and to view this as a problem and responsibility of all of us, as it will help to maintain production and consumption of this delicious food product as a social, nutritional and healthy value to our society.

José Alba Mendoza
Doctor in Chemistry. Olive Oil Production Expert