AUSTRALIAN OLIVE OIL PRODUCTION
Olive oil is literally the naturally extracted juice of a fresh olive. The basic principle of making olive oil is to extract the valuable oil from olive flesh (mesocarp). This extraction process centers on naturally separating the oil and other liquids (water) from the solid material. Below is an outline of the full olive oil production process. In Australia, this process usually takes between 6 to 12 hours from the time the olives are harvested time the oil is pumped into tanks.
1. Harvesting the olives
When the olives have gained the required flavours, aromas and oil levels, they are ready to harvest. Picking olives can be done by hand, with vibrating rakes or using machine harvesters. In Australia, the majority of olive groves are harvested using special olive harvesters that have been adapted for Australian conditions.
2. Cleaning the olives.
Once the olives are picked, leaves, stems and twigs are removed. The olives are often washed with water to remove unwanted foreign matter (dust, sand and pesticides) that may affect the flavour of the oil and damage the oil extracting equipment.
3. Crushing the olives
The olives then need to be crushed to break up the flesh and cells of the olive. This will produce a paste with tiny droplets of oil. Traditionally this was done using stone rollers or wheels that rolled in circles on a slab of granite to grind the olives into a paste. Some olive growers in Europe still do this, however in Australia, producers use metal crushers that rotate at high speed pushing the olives into the sides of a rotating compartment.
4. Mixing the olive paste - Malaxation
Mixing or beating the paste prepares the paste for separation of the oil from the pomace. The most common mixer is a horizontal trough with spiral mixing blades. This takes between 20 to 40 minutes, and in this time, small oil droplets combine into bigger ones which can be removed in the next step. It is an important step as it maximizes the amount of oil to be extracted from the paste.
The paste is often warmed to 28°C during this process. This helps to decrease the oil’s viscosity and improve water oil separation, thus increasing the oil yield. However, heating can also lead to increased oxidation and shorter shelf life of the oil.
5. Separating the oil and water from the olive paste (pomace)
The next step is extracting the olive oil from the olive paste. Traditionally, the olive paste was put on round mats which were then stacked and pressed using a long lever weighted with stones or with a screw olive press. In Australia, the most common way to extract the oil is through centrifugation. Centrifugation uses very high-speed centrifuges that extract the oil from the beaten paste through a fine screen. The centrifugal decanter spins the olive paste in a horizontal drum; the pits and heavier olive flesh move to the outside and the liquids (water and oil) are tapped off from the center.
6. Separate and remove the oil from the water
Now the oil needs to be removed from the water. In Australia, this is done in two ways. Firstly, the oil and water is put into tanks where they separate and settle by gravity. The oil floats to the top of the tank and the water to the bottom. When it has settled the water is drained from the bottom of the tank or the oil is pumped into another tank, leaving the water behind.
The second method is to use a centrifugal olive oil separator. This is like a cream separator in a dairy where the liquid is spun at a high speed which separates the heavier water from the lighter oil. The oil is then pumped into a stainless steel tank to settle.
7. Oil Storage
Historically, olive oil was stored in ceramic amphorae; however olive oil can be stored in containers as unexciting as plastic or as imperishable as stainless steel. In Australia oil is most commonly stored in stainless steel tanks. These can range from 100 litre drums to 100,000 litre tanks. In Australia, nitrogen or carbon dioxide olive oil is often used at the top of tanks to stop the olive oil coming in contact with air. This delays oxidization and rancidity.
8. Processing the Olive Oil
Finally the oil is ready for grading. If the olive oil is not extra virgin or virgin quality it is most often processed further. It is processed three different ways. Firstly the oil is refined using steam or an alkali. The purpose is to reduce free fatty acidity level and improve the flavor of the oil.
It is then bleached using diatomaceous earth to reduce or remove colour (chlorophyll), carotenoids, residual fatty acid salts and any high levels of pesticide residue. Finally the oil goes through a process of deodorization using activated carbon which reduces any odors. The outcome is a neutral oil that is tasteless, colourless and has no aroma. This is used to make light, extra light and pure olive oils.
