In our area, farmers harvest olives in different ways, but the main one is through BEATING. Hitting the trees with the help of a long pole, they knock the olives down on a net placed just underneath. Another usual way is hand picking, or MILKING. For this technique they use the popular “macaco” (a basket) around the chest. It is usually done on a ladder leaning against the olive tree. A recently widespread way is the VIBRATING. This system can only be applied in young olive trees and normally the “carrasqueña” olive variety.
A mechanical arm attached to the trunk makes it vibrate so that the olives fall on a tarpaulin which the arm itself has in order to be collected into a basket or a trailer later on. There are other ways but these are the main ones. We must stress the fact that in order for the olives to be harvested by these techniques, they must be ripened since, with the exception of the MILKING, they all imply hitting or shaking to help with the fruit falling. There is also the manual vibrator which operates in a similar way as the above mentioned except just with one branch.
Harvested olives are transported in trailers or plastic containers.
This process is completed in our mill. The farmer delivers the produce in a hopper, where the olives are cleaned. First, leaves and dirt are removed from the olives, followed by the removal of wet mud, stones and other debris. Finally the olives are dried and weighed.
The olives are weighed once they have been cleaned, using an electronic scale weighing at 100 kilogram pulses. A conveyor belt raises the olives to the storage hopper.
Olives are stored for as short a time as possible to ensure the olive oil produced contains all the natural benefits of the fruit.
In the past the grinding was done with conical stone rollers which, after the olive has rested for 12 hours, crushed the olives with their weight. Such force would make a paste accumulate on the sides and, gathered by blades, would be taken to the mixer (second stage).
Today the usage of rollers in mills are not very common, as their maintenance, cleaning and replacement are very complicated, and the grinding process very slow. Although good, it is not efficient for processing large quantities of olives.
Olive oil extraction methods have changed man times in history, from the Roman presses to the not so ancient rollers like that housed in our museum. The arrival of decanters allows the mill to produce the quantity of oil in half the time, a not insignificant improvement. Not only is the extraction process faster, but the quality of the extracted oil with their aromatic properties is also improved.
We can utilise two processes to separate the oil from the pulp and water. The first is a more traditional method, making use of a hydraulic press. During this process, the olive pulp is spread over stacks of round mats (“capachos”), which acts as a natural filter, allowing the liquid to run through and trapping the solids. The straw mat, now called a “foot”, is moved to the hydraulic press, where the pressure generated causes the pulp to compact in the straw mat, and the liquids forced out.
A very fine, vibrating sieve beneath the stack of mats, keeps the smaller solid particles from mixing in with the liquids and passing to the centrifuge.
The olive pulp (alperujo) that remains in the mats, has an olive oil content between 3% and 5%. This is stored in a hopper and transported to another factory that uses it in the production of pomice oil.
The process we currently employ makes use of a decanter. This process can be completed in half the time as the previous methods, resulting in a final product that retains more of its natural characteristics and aromatic properties.
The decanter, a stainless steel cylinder, holds the pulp at a controlled temperature, and allows the separation of solids, water and oil by gravity. From here, the oil that is resting on top of the water and solids, is removed, and sent to natural decanters or the centrifuge.
This process completely cleans the extra virgin olive oil of the water naturally contained in the olive, and the remaining small solid particles, to make it suitable for consumption. In former times, decanting was the only possible system to obtain clean olive oil. This process allowed the separation of oil, water and particles in large tanks, with oil staying at the top, followed by the water and solid particles. The upper part of these storage tanks are connected to vessels, allowing the olive oil to slowly flow from one to another at temperatures between 15ºC and 18ºC to the last decanter, practically clean.
In modern times, a Centrifuge is used, that requires the use of water no more than 30ºC. As the Centrifuge turns, water and small solids are separated to one side, and the oil to the other.
Usage of decanters started to decrease due to the centrifugal process taken from the dairy industry. A German company incorporated this system to the olive oil process, improving the olive oil extraction and storage time with at least 2 days, while also decreasing the storage space needed.
It has also been proven that the use of a centrifuge during the production of extra virgin olive oil limits the loss of the oil´s natural qualities, while also improving the quality of the stored product.