1. Harvesting - The olives are harvested when they are at the perfect stage. Nothing gets more discussion among Growers and Miller's. Timing affects the yield, the taste, shelf life and color. They are usually picked when the tree has a combination of ripe vs. unripe olives. This is the Grower/Miller's gift...to know the correct timing for their individual oil. Some oils consist of more ripe fruit which makes the oil milder and less pungent or some like to pick when the olives are a larger percent of green fruit which creates a more pungent, bitter, robust oil. The best oils come from clean, unblemished, fruit, they don't pick up any rotten fruit that has fallen and started to ferment.
2.Transportation - Once picked they are taken to the mill. The fruit should be stored for the briefest of time in small, plastic containers which allow plenty of air to circulate around the fruit and not too many olives are piled on top of each other so they don't get crushed before reaching the mill. In the best cases the mill is on-site or at least close by and the fruit is crushed within hours of picking to ensure quality and freshness. Handpicking vs mechanical?? depends...in some cases hand picking is kinder to the tree and avoids breaking too many branches but not always. There is some amazing equipment that can be gentle to the tree and still remove the fruit carefully.
3. Washing - Generally, the fruit is washed. It is cleaned only with clean water (never any chemical solvents!) and all stems, leaves and branches are removed before washing.
4. Crushing - The fruit and pits typically get crushed. This process helps to get the fruit to release the oil from the vacuoles. In modern facilities it is done with metal tooth grinders, different kinds of hammermills or in the older method with stone mills.
5. Malaxation - The fruit goes through the malaxation process (mixing). This is the process where the paste is mixed for the perfect amount of time (again the Miller's gift is to know that timing) This process helps to create aromas and also releases phenols (powerful anti-oxidants) In this process you take oil which is dispersed in water and over approximately 45-90 minutes (some Miller's do run it longer) it slowly gets small drops of oil to become bigger drops and thus converts to a product of water dispersed in oil (inversion) The goal is to do the process long enough to release the aromas and phenols but, quick enough to prevent too much oxidation (although you do need some oxygen to release the aromas and complex flavors)
6. "The Press"- or nowadays a Vertical Centrifuge/Decanter is used to separate or "decant" the water and solids from the oil. Some centrifuges are three-phase because they remove the oil, the water and the solids separately or there is a two-stage which separates the oil from the wet paste and often the oil coming out of the first centrifuge is further processed to eliminate any remaining water and solids by a second centrifuge that rotates faster. Older methods use mats to squeeze the paste to separate the oil and water from solids. This old method is not considered optimal because you can never clean these mats perfectly between crushes and therefore you will always have rancid oil contaminating your new run. This oil will always have a defect in it and by definition would not be considered an Extra Virgin Olive oil. Even if an oil comes from a small farm growing their own olives it may not be the best quality oil because of how it is handled after the harvest and in the milling.
7. Settling - also called racking is when the oil is left to settle naturally with gravity over 7-10 days and sediment that falls to the bottom is removed.
8. Filtration process - this is where the oil is run through earth filters and cellulose, paper or cotton filters to create a clear oil. Not all oils are filtered and many times if the proper settling and storage times have been observed and most of the sediment has been removed it is not done. Filtering helps extend the shelf life of an olive oil and make a consistent product but, it also removes some of the flavors and aromas.
9.Storage - oil is stored in giant tanks where another separation happens naturally with gravity.Sometimes these tanks are topped with nitrogen to prevent a gap of oxygen at the top of the tank which will speed up the oxidation of the oil. The oil is stored for as short a period of time as possible just enough to make sure it settles approximately 45 days and then can be blended and bottled and shipped.
Note: unfiltered oil is not necessarily bettter oil. Yes it is good because if it is fresh as in Olio Nuovo it can contain good little bits of pulp in the oil and this NEW oil is always when the oil has it's highest levels of anti-oxidant phenols but.....bits of pulp create fermentation and this oil goes rancid quicker than filtered oils, so if you buy it you must use it within a month or two of harvest or don't buy this type of oil!! This oil has a very short shelf life.
10. Bottling - the oil is bottled and shipped.
Note; the paste that is left from this "first press" is sometimes then pressed again to create Virgin Olive Oil or lesser quality grades of olive oil. The second press is usually done at high temperatures to release as much of the oil remaining in the paste and then often needs refining to remove any defects before being blended with other oils.