OIL EXTRACTION PROCESS

PREPARING THE PASTE

For 12 months before the olives are harvested, the olive trees must be nurtured and cared for in order to obtain a healthy and abundant crop.

The process by which oil is formed and accumulated in the fruit is called "lipogenesis" and is highly influenced by agricultural factors and climate conditions. Expertise, experience and use of a laboratory are needed to determine when this process has been completed and, therefore, when the best time is to harvest the olives. (See image)

From this first moment, it is important to focus on quality, as harvesting involves several factors that are not entirely compatible with each other, such as obtaining a healthy, quality product and collecting the highest amount of oil possible while causing the least amount of damage to the tree during harvesting.

In our drive to achieve excellence, our harvesting procedure is as follows:

  • 1- We harvest early when the trees have the highest amount of ripening fruits and the highest percentage of polyphenols and volatile compounds that can express a wide and complex array of sensory qualities.
  • 2- We harvest olives using mechanical methods (a harvester for super high-density groves and an 'umbrella' device for traditional groves) and only collect fruits that are still on the tree.
  • 3- The olives are transported to the oil press extremely carefully in just a few minutes, as it is located near to the olive groves. As soon as the olives arrive, we start the process to extract the oil. This means that there is no waiting time and the olives do not have to be stored.

Receiving, unloading, cleaning (with or without washing) and weighing the fruit.

The unloading process begins once the quality of the fruit has been checked. This is done using a grate attached to a stainless steel intake hopper that is located in a pit on a 0.5 metre, three-sided plinth. This plinth is raised above the ground to prevent foreign objects from falling into the hopper and so that vehicles cannot be driven over the top of it. From this moment onwards, the olives travel along conveyors fed by stainless steel belts. In order to make the process as hygienic as possible, we have removed all types of augurs from the device used to transport the olive paste and replaced them with different types of pumps.

The olives then pass through the compact cleaning system, which removes leaves, small branches and stones. The olives will be washed if necessary. Then, they will be weighed and transported to the hopper before being pressed.

The process used to extract high quality extra virgin olive oil is complicated due to variations in the olives. Although they may be of the same variety and from the same source, their properties may vary from day to day as regards moisture and percentage of oil and pulp, which means that the extraction process has to be continually adapted.

We use a cold extraction system that involves a two-phase centrifuge process. This is also sometimes known as an 'environmentally friendly centrifuge process', as it uses less water and does not produce liquid waste.

The process can be divided into three major phases:

  • Preparing the olive paste. This involves pressing and mixing the paste.
  • Separating solids from liquids by extracting the oil from solid waste, which is currently done by a decanter.
  • Separating liquids from liquids, which takes place in the vertical centrifuge by cleaning the oil and removing moisture, impurities and any fine solids that may remain.

The purpose of pressing is to break the fruit's plant tissues to release the oil contained in its mesocarp vacuoles and make a paste from the pulp, stone, oil and vegetable water.

This process is performed by a stainless steel rotating mesh hammer press. Care must be taken as regards certain aspects of the process:

  • The paste must be of a uniform nature (to help with mixing).
  • The olives must be pressed to the right consistency (to obtain medium size particles). If the particles are too large, this means that the cells containing oil have not been sufficiently broken, and if they are too small, it will be very difficult to extract oil from the resulting mush. The olives are pressed to the right consistency using meshes with different sized holes. These meshes usually have diameters of between 4 and 5 mm at the start of the season, which increase to between 6 and 7 mm as the season advances.
  • The paste must be prevented from over-heating due to friction.
  • The speed of the press must be adapted to ensure as little air as possible enters the paste.

We make an oily paste by binding the drops of oil together. To do this, we use mixers equipped with paddles that rotate at a constant speed in order to mix the paste to enable the drops of oil to blend. These mixers are heated by passing water through a double-walled area.

At Alguijuela, we have a mixer with three separate containers, each with a capacity of 600 kg, that are surrounded by thermal glass and equipped with a self-cleaning system, water inlet and a comprehensive temperature control mechanism.

This is the most critical part of the process. Once again, we have to take two opposing factors into account, this time 'quality versus quantity', and to do this, we must monitor three different variables:

  • Paddle Rotation Speed: If the paddles turn too quickly, too much air will enter the paste, which will lead to oxidation. However, if they turn too slowly, the paste will not be churned enough.
  • Mixing Time: Mixing the paste for too long causes the number of polyphenols to decline, which makes the oil less stable. However, if it is not mixed long enough, the small drops of oil may not blend together to create larger drops.
  • Temperature of the Paste: It has been clearly demonstrated that more oil can be extracted if the temperature is increased. However, increasing the temperature has a negative effect on the quality of the oil obtained.

To obtain the best extra virgin olive oil, a cold extraction process must be used. Cold pressed extra virgin olive oil is extracted at temperatures of less than 27 Degrees Centigrade.

Temperature has a major impact on oil quality. An oil's aroma stems from the volatile compounds in it. More volatile compounds evaporate at higher temperatures, which means the oil loses its aromas and flavours. Using the cold extraction process also reduces the rate at which the paste oxidises, which results in oils with a lower acidity.

The separation of solids and liquids takes place by means of a two-phase centrifuge process using a decanter, which is sometimes also called a 'continuous extractor'. Decanters are horizontal helical centrifuges with a solid liner. They separate materials according to density.

In this instance, there are two phases:

  1. The light phase (i.e. the oil) occurs close to the axle.
  2. The solid phase (i.e. the pulp, crushed stone, vegetable water, etc., which forms the mass of waste materials known as 'Alperujo') occurs along the walls of the cylinder.

This waste is collected in containers that are taken away by agricultural waste removal firms to be subsequently treated and used. The oil generated by the decanter is collected in a vibrating filter, which removes any solids that may be suspended in the oil, and then transported to the vertical centrifuge by a non-emulsifying pump.

This separation process takes place in the vertical centrifuge using a centrifugal force. The oil is 'cleaned' inside a plate rotator to remove moisture and any fine solids or impurities that may remain.

The centrifugal force separates the liquids (oil and water) in a drum at a rate of 6,200 revolutions per minute and minimum power of 2.2 Kw. The water drains out through a pipe at the back of the machine, while the oil is removed via a wide aperture located at the top of the machine on the front, ready to be transported to the depot.

To ensure the extra virgin olive oil produced at our facilities remains in perfect condition, the oil is stored in small stainless steel tanks that are conical in shape to help remove moisture and enable the impurities caused by fermentation to decant and sink to the bottom of the container.

The tanks differ in size (10,000l, 5,000l and 2500l) and are kept in a dark environment at a mild and constant temperature.