To do this, mechanical or physical means can be used, but they must not cause alterations to the oil produced.
Depending on the type of processing, it can be defined as a continuous cycle mill (also called modern) or a traditional or discontinuous cycle mill (with stone presses and millstones).
Generally speaking, we have different phases that mark the activity within an oil mill :
- The olive harvest, which takes place during the olive oil season : the olives are picked from the trees, usually using combs or special rakes. The olives are collected in bags or crates and transported to the mill.
- cleaning the olives : the olives are cleaned to remove any debris, branches or leaves;
- Crushing : this is the central phase of oil production. Here, the olives are crushed to break the pulp cells and thus release the oil contained within. The resulting olive paste is then placed in a press;
- Pressing : the olive paste obtained at this point is moved into a press, where the oil is separated from the solids. The resulting oil is collected in special tanks, while the solids (the pomace) are collected in special containers.
- Decantation : the resulting oil is left to settle for a few days, allowing the solid particles and water to separate from the oil. The clarified oil is then separated from the lower layers of "dirty" oil;
- filtration : the oil is filtered through fine-mesh filters, in order to eliminate any residual particles and improve its clarity;
- Storage : the oil is stored in special bottles or cans, away from light and heat, in order to preserve its organoleptic properties.
The work carried out within an olive oil mill has an ancient charm that has been handed down for centuries and which over the years has been integrated with improvements and more modern supports.
Each stage of the olive oil production process requires care and attention to ensure the quality and purity of the final product and varies depending on whether the mill is traditional or modern.
Crushing olives with the hammer mill and the disc mill
The crushing process, illustrated above, can be carried out in two ways: with a hammer crusher and with a disc crusher.
What changes?
- The hammer mill is a large steel cylinder. The olives are placed inside it, then crushed by large moving hammers. The hammer mill is typically used for the production of artisanal olive oil because it allows the olives' organoleptic characteristics to be preserved intact.
- The disc mill is a larger and more complex facility: here, the olives are passed through a series of discs that crush them. They are then fed into a hopper, from which they pass through a series of rotating disc crushers, where the paste is crushed and the oil particles are released.
Differences between an old-fashioned oil mill and a modern one
The history of olive oil in the Mediterranean basin is ancient; the first olive presses date back centuries, but over the years, olive pressing methods have changed and become more modern.
Traditional oil mills , also called discontinuous mills, are oil plants that use stone wheels (called millstones ) to crush the olives.
The olives are crushed using mechanical pressure, while the extraction of the olive oil is entrusted to pressing and mechanical pressure (using hydraulic presses).
How is olive oil extracted in a traditional mill?
- the olives are washed and defoliated
- stone wheels (millstones) are used to crush the olives
- the paste obtained through dosing machines is distributed on discs of fibre (today synthetic, once of vegetable fibre) called fiscoli , which are placed one on top of the other in a pile on a trolley
- the trolley is then taken to the press to obtain the oil by mechanical pressing
In a modern oil mill , such as Frantoio D'Orazio, cutting-edge methods are used to crush their olives.
Not much time must pass between the olive harvest and their transfer to the mill: the olives are immediately taken to the plant, this guarantees the production of quality oil .
During the olive oil harvest, the olives are often paid for by the mill. The price is not standard but varies from year to year based on the quality and success of the harvest, as determined by the vintage.
What are the advantages of a modern oil mill?
Adopting modern methods for pressing olives brings several advantages:
- limited space requirements for all the machinery that makes up the mill
- All the stages of processing and transformation of the olives take place in a continuous cycle, which leads to an enormous saving of time: in fact, there are mills that can process 500/1000 quintals of olives in just 24 hours.
- significant reduction in manpower employed
- Machinery cleanliness, essential for quality oil, is improved. Modern mills offer the option of programming automatic or manual washing, thus avoiding the risk of contamination between batches of olives (especially for those mills that work for third parties, which are the majority). The result is a higher-quality oil and greater hygiene.
- Less exposure of the olive paste to oxygen, which can cause oxidation. By less exposure, we mean both the surface area and the time required.
- processing times are reduced
Currently in Italy there are approximately 5,000 existing oil mills , 20% of which use the traditional system (called pressure) to extract oil, while the rest of the plants are of the continuous cycle type with two phases and three phases.
Frantoio D'Orazio uses a two-phase extraction process which includes:
- no use of water during the process
- At the end of the extraction cycle, virgin pomace is obtained (composed of olive stones, pulp residues and peel) and oil must.
Traditional mills still exist, but the latest generation mills are preferable for all the advantages just illustrated.
A modern olive oil mill is a large investment: the average cost is 400,000 euros.
Of the 5,000 oil mills in Italy, approximately 939 active oil mills are located in Puglia and process 53 varieties of olives.
Not only that, but Puglia is the Italian region that holds the record for olive oil production, with 66 million olive trees! In second and third place are Calabria and Sicily.
The Apulian oil mills are distributed across all 6 provinces: Province of Bari (228 active mills), Lecce (251), Brindisi (143), Foggia (136), Barletta-Andria-Trani (84), Taranto (97).
(Data source: Agea, 2014-2015 Campaign)
