The method of extraction has a distinct effect on the flavor and ultimate quality of the olive oil. The basic procedure has remained the same for thousands of years. It involves crushing the olives into a paste, separating the liquid components from the solids and then further separating the liquid components into its constituent parts: vegetable water and olive oil. The mechanical process has undergone numerous changes and refinements that have increased both productivity and quality. The machinery and technique of olive oil extraction continues to evolve, promising continued improvement in both quality and efficiency.

The following methods of extraction are in common use today. Some of these methods are rapidly disappearing as mills modernize and retool. Some older methods of extraction impart a distinct flavor that some old timers consider a sought after attribute. In contrast, this same flavor is considered by some proponents of the modern continuous method as a defect, proving once again that “beauty is in the eye of the beholder.”

STONE GROUND, MATT PRESSED - This method is rapidly disappearing because of higher labor costs and lower yields. It involves crushing the olives into a paste with rolling stones on a revolving axle and pressing the paste through woven mats with the aid of hydraulic presses. The solids are trapped inside the mats and the liquids drain down the outside of the mats and are captured in basins underneath the press. The vegetable water sinks and the oil is siphoned off the top. The mats are emptied of the pits and skins and “re-buttered” with fresh olive paste and the process is repeated. This method results in very sweet oil with slightly higher levels of acidity. The mats impart a distinct flavor from the bacteria and mold that grow with their repeated use. Many old timers insist that this flavor is an absolute must in fine olive oil.

CONTINUOUS METHOD- This is by far the most widespread method used in the world today. Olives enter the mill at one end and oil comes out the other. The olives are crushed by hammermill and the paste is pumped to a malaxer where it is warmed and beaten or mixed until the oil begins to separate. The paste is then pumped to a centrifuge where the solids are separated from the liquids. The vegetable water and oil are further separated in a final centrifugal process. There are lots of variations on this basic set up and theme that involve less heat and less “cleaning or washing of the oil.” The polyphenols that account for the flavor in olive oil are much more soluble in water than in oil. Consequently, the less contact the oil has with water the better and more flavorful the oil will be.

INTEGRALE- This method is virtually identical to the CONTINOUS METHOD with the notable difference that the olive pits are removed from the flesh before the oil and water are extracted. This method has existed for thousands of years but the cost and time to remove the stones prior to extraction were cost prohibitive. In addition, there is a slight loss in yield. Proponents of the integrale method claim less bitter oil with fewer toxins and waxes as well as the added economic advantage of ending up with four valuable and marketable products instead of one. The benefit of eliminating the environmental degradation (a major issue and problem where large amounts of vegetable water become pollutants) is significant. This method of extraction is considered cutting edge. It promises to become widespread if all of its potential benefits are realized.

For more information on the integrale method visit: http://www.supremooil.com/integrale.html.

For more information on olive oil processing visit: http://www.agric.wa.gov.au/programs/hort/olives/processing.htm.