When You're Anoited

It’s time for the oil to flow!

I Picked for Purpose

*WHEN ARE OLIVES HARVESTED?

When cared for properly, olive trees produce fruit every year. Harvest season traditionally runs from August through December, with green olives picked early in the season and black olives picked toward the season’s end. That’s right — green olives and black olives come from the same trees. There’s no difference in the olives themselves; the color difference is an indicator of the olive’s ripeness. But more than just determining the color of the olive, the maturity at the time of harvest plays a major role in the quality of the olive oil that is eventually produced.

When green olives are harvested at the peak of their ripeness — usually a two-to-three-week period in late August or early September — they produce the most vibrant flavors and contain the highest levels of polyphenols. As they ripen further, the flavors and healthy compounds decrease quickly. Due to this degradation, the highest-quality extra virgin olive oil will always come from olives harvested early in the season.

There is a trade-off with harvesting olives at their peak ripeness. Olives harvested at their peak contain less oil. The more an olive matures, the more oil it contains. For that sake of maximum yield, many olive oil producers allow lower quality olives to go past peak ripeness, a decision that increases the amount of oil extracted from each olive but decreases the fresh flavor and nutrient content of the olive oil produced.

II Cleaned for the Course

*CLEANING THE OLIVES The first step in the oil extraction process is cleaning the olives and removing the stems, leaves, twigs, and other debris left with the olives. The olives should be washed with water to remove pesticides, dirt, etc.  Rocks and sand will damage a hammermill and quickly wear out a centrifugal decanter or oil separator, reducing life span from 25 to as little as 5 years. It is amazing, and sometimes entertaining, to see what can be found in the bins with the olives. We have heard millers talk not only about rocks and branches, but broken glass, rings, bracelets, pieces of metal, knives, and even razor blades. Light contaminants are removed by a heavy air flow (blower) and heavy objects sink in the water bath.

III Crushed for Cooperation

*GRINDING THE OLIVES INTO A PASTE The second step is crushing the olives into a paste. The purpose of crushing is to tear the flesh cells to facilitate the release of the oil from the vacuoles. This step can be done with stone mills, metal tooth grinders, or various kinds of hammermills.

*MALAXING THE PASTE Malaxing (mixing) the paste for 20 to 45 minutes allows small oil droplets to combine into bigger ones.  It is an indispensible step.  The paste can be heated or water added during this process to increase the yield, although this generally results in lowering the quality of the oil.  The most common mixer is a horizontal trough with spiral mixing blades. Longer mixing times increase oil yield but allows a longer oxidation period that decreases shelf life.

IV Separated for Service

*SEPARATING THE OIL FROM THE VEGETABLE WATER AND SOLIDS How is oil separated from vegetable water and solids?The next step consists in separating the oil from the rest of the olive components. This used to be done with presses (hence the now somewhat obsolete terms first press and cold press), but is now done by centrifugation, except in old facilities. Some centrifuges are called three-phase because they separate the oil, the water, and the solids separately. The two-phase centrifuges separate the oil from a wet paste. In most cases, 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. The oil is then left in tanks or barrels where a final separation, if needed, happens through gravity. This is called racking the oil. Finally the oil can be filtered, if desired.