Extra-virgin Olive Oil Extraction: The Olive Mill
Are you curious about how extra-virgin olive oil is produced? What actually happens to the olives when they get to the olive mill?
In this article, we are going to take you through our process of turning olives into excellent EVOO.
- From the Field to the Mill: Transportation
- The Milling Process
Naturally, there are all different kinds of mills. But today we are going to talk about the one we use here at Fattoria Triboli. These are some of the features of the mill we use:
- Continuous-cycle: to minimize oxygen contamination during milling
- Two-phase extraction. The decanter produces two substances: oil and moist olive pomace
- Cold-pressing: The entire process takes place at controlled temperatures below 27°C / 80 °F
Let’s take a closer look at the steps to extract EVOO.
- FROM THE FIELD TO THE MILL: TRASPORTING THE OLIVES
During the day, we harvest the olives in the field. Then we put them in boxes that weigh roughly 20 kg each in order to allow airflow around the fruit and prevent premature fermentation.
The boxes of olives are then transported to the oil mill. Here, they are weighed so that, after they have been milled, we can calculate yield, i.e. the relationship between the amount of oil extracted and the olives.
After weighing the olives and ensuring their quality, they are ready for the mill!
- THE MILLING PROCESS
How many times have you wondered, “How do you extract oil from olives?” It is not as easy as it is with oranges, which you just have to squeeze for the juice to come out. With olives, it is a little more complicated. The oil particles are trapped inside tiny vacuoles within the fruit. And to extract the oil you need to break down these vacuoles.
Let’s look together at the milling process and the equipment used.
2.1 THE CONVEYOR BELT AND THE WASHING MACHINE
Once the olives have been weighed, they are ready to go into the hopper (a large upside-down funnel) connected to a conveyor belt that slowly feeds the olives into the washing machine.
Before dropping into the water, any leaves are removed from the olives using a leaf removal machine that blows them out of the milling system.
Now, the olives go into the washing machine. Here, they are washed with potable water. This removes any impurities that may influence oil quality during processing.
Next, the olives are transferred onto a drying belt to reduce the risk of water entering the mill to a minimum.
2.2 BELT ELEVATOR
When the olives are dry, they fall into another hopper and slide through a spiral tub into the mill. Here, we do another quality check to remove any residue remaining after the proceeding phases (like leaves, branches, small stones, unhealthy olives, etc.).
2.3 THE MILL
Continuous-cycle milling minimizes oxygen contamination, which is actually very high in traditional, discontinuous-cycle milling. In this last method, olives are milled using millstones and grinding stones that press the olives using their own weight. Nowadays, this method of milling is obsolete and hardly ever used.
Modern mills may have rotating disks, hammers, or blades. Which one you use depends on a range of variables (how ripe the olives are, olive variety, the type of oil you wish to obtain, etc.).
2.4 MALAXERS
After the mill has converted the olives into a fine, uniform paste, the malaxing process begins. Malaxers are either horizontal or vertical vats that collect the olive paste. Inside these vats are rotating blades that slowly and continuously churn the paste.
This process causes the oily parts of the mixture to separate from the watery parts. This phase lasts from 10 to 45 minutes depending on the mill and the olives (the quality of oil you want to obtain, olive variety, type of paste, etc.).
2.5 THE DECANTER
Now, we are going to talk about the most fascinating part of the mill: the decanter! It is fascinating because this is where we will see our oil come out! The decanter is a centrifuge. Inside the frame is a horizontal cylinder. The olive paste flows inside this cylinder, where it is quickly spun to force the moist pomace (a paste with no oil content) to the outside.
. Because this paste is heavier, it gradually separates from the oil, which remains inside the vortex.
Now, the oil flows out through nozzles on the wall of the cylinder. These nozzles look a bit like straws that go though this circle of material: first the pomace, then the water, then the oil. This “straw” enters through the oil layer, allowing the oil to flow out of the centrifuge.
Now, the oil is collected in a vat, then pumped into a press filter, which removes all impurities.
Now, the oil is collected in a vat, then pumped into a press filter, which removes all impurities.
Then, it’s done and all you have to do is taste the new oil!
Have you ever seen an olive mill in action? It’s never too late. You still have time to visit a nearby olive mill to see what you’ve learned from this article with your own eyes!