Azienda Agraria Giusy - Harvesting and milling
Our company uses the technique of manual olive harvesting with the aid of pneumatic harvesters.
From mid-October, we begin carefully harvesting this precious fruit, paying close attention to the ripeness of the olives and the mapping of the cultivars present in the plots. Our harvest does not involve the use of machinery that shakes the entire tree so as not to cause damage to the roots.
Following the harvesting, an operation called sifting of the olives takes place: this operation is carried out to remove branches, leaves and undamaged olives that could alter the quality of the product.
After sifting, the olives are ground within 24 hours in order to retain nutrients and ensure optimal flavour.
The mill, located just a few hundred meters from the farm, is certified for processing oil designated for protected designations of origin (PDO) and holds organic milling certification.
The cold extraction of the oil is carried out using two methods:
- Sinolea extraction
- Centrifugation extraction
Sinolea extraction
The Sinolea is a device integrated into a specific continuous-cycle system that operates using a process different from other systems. The physical principle on which Sinolea is based, conceived since 1911, is the difference between the surface tension of the vegetation water and that of the oil: due to this difference, the oil tends to easily adhere to a metal surface compared to the water, which is separated through percolation. The extraction method is also known as percolation or selective filtration.
Sinolea fundamentally consists of a tank containing the oil paste, produced by a hammer mill, into which the extraction device is immersed. The device consists of a series of several thousand steel blades, which are immersed in the oil paste with a continuous alternating motion that cyclically goes through the following phases: immersion-lifting-removal of the oil.
At each immersion cycle, the lifting of the device causes the vegetation water to drain due to gravity while the oil adheres to the metal surfaces. The evaluation of the extraction method reveals advantages related to product quality and operational aspects. The qualitative advantages are due to cold processing and the absence of interference with the biochemical characteristics of the oily fraction of the olive pulp, such as “washing” of polyphenols or alterations caused by improper cleaning of the diaphragms: this allows for the production of high-quality oils with high levels of aromatic substances and polyphenols.
In contrast to the above-mentioned advantages, there are disadvantages related to low yields, an intrinsic aspect of this process. The specific yield depends essentially on the water/oil ratio in the processed olives and may even be less than 50 per cent of the total theoretical yield. This makes it necessary to combine Sinolea with a plant that allows extraction by centrifugation of the residual paste, with a consequent increase in processing costs.
Centrifugation extraction
This is a widely used method because it overcomes the many disadvantages associated with pressure extraction. The oil paste is subjected to centrifugation in a rotating conical drum with a horizontal axis (commonly called a decanter). Centrifugation generally operates at a rotational speed of 3000-3500 rpm. Due to the different specific weight, centrifugation separates 2 or 3 phases.
The 2-stage decanter is designed to overcome the drawbacks of the 3-stage system. In practice, it differs in that it uses less water. Centrifugation separates only two fractions:
- the pomace and the vegetation water;
- the oil must, containing a small amount of water.
The system reduces the pollutant load problem because the quantity of polyphenols extracted is lower. However, it has the defect of producing excessively wet pomace, which is not accepted by pomace factories because it has little commodity value. The pomace therefore becomes a waste product to be disposed of without any possibility of economic recovery, as drying is not very convenient.
