For many producers, the olive mill is a “black hole”: we know what enters (olives) and the general outcome (oil).
Sentences such as: “I have no idea why the oil is like that (too bitter, too flat, too pungent, too green/ripe), this is the way it is this year” are common at the mill or in storage when the oil is tasted.
But olive mills are not black holes. The olive oil that comes out of the separator (or the decanter) is not a predestination, but a result of a process that we can affect and direct to our desire.

The crusher: follow the yellow brick road

The method we use to crush the olives into paste will affect the first step towards our desirable oil.

What we need to consider, record and be known about:

• The olives: temperature, size, stone/flesh ratio, water content in the fruit (below/above 50%).
• Crushing method: stone, discs, hammers, knives, combined, with or without pre-crushing, with ot without de-pitting.
• Velocity of crushing (RPM, depending on the method of crushing)
• The net: diameter of the holes, the shape of the holes (round, oval, elongated hexagon)
• Internal ambient: adding water (yes/no), cooling device, adding oxygen/inert gases

These factors will affect the first step we are taking on the road towards the requested oil:
📌 The size of the particles
📌 The temperature of the paste
📌 The temperature of the paste in the crusher will affect which enzyme groups begin to work in the kneading cell (malaxer), and these enzyme groups will determine the oil’s characteristics: aroma, taste, and color.
📌 Particle size determines how easily enzymes can break down the paste, thereby creating aroma, taste, and color.

Crushing is only the beginning of the process. If we can’t choose between methods (we have only discs/hammers/knives/stones), we can still affect the aromatic profile in the kneading cell, but adjusting the crusher to our needs will make the process later much easier.

The Malaxation phase – where magic happens

The kneading cell is the core of the mill, where the oil profile is determined. In order to have that, we need to understand two reasons for malaxation:

🖊️To extract olive oil
🖊️ To create the aroma, flavors, and taste in the oil

The oil droplets bond together due to the rupture of oil bubbles within the plant cell.

The aromas, flavors, taste, and color are created due to the breakdown of the polyunsaturated fatty acids (omega-6, omega-3) and the polyphenols.

❓ What affects these two pathways:
🖊️Temperature of the paste
🖊️Duration of malaxation
🖊️Amount of available oxygen

📌 The temperature will determine which enzymes will be active, and what type of oil we will have

📌 The duration of malaxation will determine the quantity of minor compounds in the oil, the quantity of oil, and the possibility of the creation of undesirable aromatic compounds (which are not necessarily defects, but aromas we didn’t intend to have in the oil)

📌 The amount of oxygen will determine the balance between aromas and bitterness/pungency.
We are taught that oxidation in the olive oil process is always bad, but in the malaxation phase, oxidation is fundamental.

🗒️ So many dilemmas:

Higher temperature in the kneading cell➡️less aromas and flavors, but➡️more polyphenols and color (and vice versa)

More oxygen➡️more aromas and flavors, but➡️less polyphenols and color (and vice versa)

More malaxation time➡️more minor compounds and oil (and vice versa)

⚠️ However, too much time in the kneading cell will lead to undesirable aromatic compounds, a higher possibility for the appearance of defects, and the loss of minor compounds.

What started in the crusher can now be enhanced, changed, or manipulated in so many ways: ripe Arbequina can turn highly bitter and pungent, green Picual or Coratina can turn mild or even adopt significant ripe notes. The sky is the limit, with the right equipment and the understanding of the process.

Separation – oil is coming….

For many, the separation phase seems trivial: the paste goes in one side, and on the other side, there is oil (and water and pomace). But there are many factors to consider, and the innovativeness in this phase is exciting.

Factors in the decanter:

✏️Degree of emulsion – usually in a paste from ripe olives (some varieties tend to be more emulsified than others). Adding water and/or slowing the stream of paste into the decanter will solve it

✏️Amount of water in the paste – in a paste of olives that are full of water (55% water and more). This situation will dictate slowing the stream of paste into the decanter.

✏️Temperature of the paste and of the water added to the decanter – both need to be similar to have good separation.

✏️Amount of water added to the decanter – more water will allow faster streaming (in a “normal” paste), but will lead to a loss of taste and aroma

✏️ The level of the pipes inside the decanter – the deeper they are screwed, the clearer the oil will be. That means fewer sediments, but a possible oil loss. The more open the pipes are, the more water will be added to the oil before the separator, leading to frequent separator washes and potentially water flowing into the oil after the separator.

✏️Innovative solutions: micro-talc, enzymes, ultrasound, magnetic fields, electric pulses. Some are already in industrial use, some are still being investigated and tested. In my opinion, this is where the most exciting innovations in the mill are taking place right now. It is worth following.

📋Two phases vs. Three phases:
The debate was settled, regarding the concentration of taste and aroma: two phases can increase the quantity of volatile compounds and taste by 30%-45%. The only reason to still use three phases, in my opinion, is the issue of treating the wet pomace. Some places don’t have the option of managing it well enough.

The separation is where all the good intentions and practices we had so far can be damaged. Understanding how the decanter operates is essential to the olive oil we want.

….And she’s buying the filtration to heaven (and shelf-life)

Olive oil is not “just oil”. It’s a fruit juice that holds both the keys to incredible culinary enjoyment and the seeds of organoleptic defects that will appear if we have mistreated the olive and the oil during the process. To extend shelf life, olive oil should be filtered after extraction.

Following the separator, there are three ways to walk on:

✏️No filtering: A sediment of tiny particles that remained in the oil will accumulate at the bottom of the storage receptacle. This sediment comprises particles of the flesh, peel, waxes, phospholipids, bacteria, yeasts, etc. While the oil will become clear and transparent, the sediment will eventually degrade its quality, and it won’t be extra virgin according to the international standard.

✏️Active filtration: filtering the oil with different kinds of filters: micro nets, cellulose, and Diatomaceous earth (DE). Active filtering may change a bit the aromatic profile of the oil, but it is a nuance – a small price to pay, for the long shelf life the oil will gain in return.

✏️Passive filtration: using a series of conical receptacles to filter the oil through quick sedimentation of the tiny particles. This method is costly and requires significant effort. Still, eventually, after several days of constant shifting of the oil from one receptacle to another, the sediments will be removed, and the oil will be transparent and ready for bottling. Due to the high cost and labor, it is extremely rare to find this method in use on a large scale

📝 During my professional life as an olive oil consultant, I met many producers who believe that filtration spoils the oil. That it removes essential aromas and even some of the oil’s “identity”.

That is an unfortunate misconception.

Refusing to filter the oil, or even worse, selling it with the sediment at the bottom of the bottle, will lead to the appearance of defects during the year after extraction.
A correct process for extra virgin olive oil must include filtration.

The process in the mill, from olives to oil, is the final step of our wishes and plans as olive oil producers/millers/farmers.

We have to ask ourselves: “Do we know the parameters of every step? What can we modify in the mill to achieve the oil we want?

Many times it won’t be 100%, but when we know what we want, and we are willing to learn how get there, we can start directing the oil to our desired outcome

‼️Master the process, and you master the oil

Ehud Soriano, olive oil consultant

L’article en français Percer les mystères du moulin