The basic procedure making olive oil has remained the same for thousands of years: harvest at the right time, crush the olives into a paste, separate solids from liquid components, and further separate the vegetable water from the oil. Extraction methods have a direct effect on the flavor and quality of the olive oil.
The stone grinding and matt pressing method is still used but has the drawback of intensive labor and lower yield compared to modern methods. Olives are crushed to paste between revolving millstones and the paste is then spread on woven mats, stacked in a press and squeezed until the fluid component is recovered in basins underneath the press. The vegetable water sinks and the oil is skimmed off the top. The mats are emptied of the pits and skins and “re-buttered” with fresh olive paste to repeat the process. This method creates a very sweet oil with slightly higher levels of acidity. The mats add a distinct flavor from the cultures that enhance with repeated use. Many traditionalists believe that this flavor is an absolute necessity to make fine olive oil but considered a defect by enthusiasts of modern president methods, proving once again that beauty is in the eye of the beholder.
The most widespread method used today is the continuous method Olives enter the mill at one end and oil comes out the other. The olives are crushed by hammer mill and the paste is pumped to a malaxer where it is warmed and mixed until the oil begins to separate. The resulting paste is pumped to a centrifuge where the solids are separated from the liquids and the vegetable water and oil are further separated in a final centrifugal process. There are many variations on this basic theme that involve less heat and less washing of the oil. Polyphenols account for the flavor in olive oil. They are much more soluble in water than in oil, so limiting contact with water preserves the flavor of the oil.
The Integral method is virtually identical to the continuous method with the notable difference being that the olive stones 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 manually remove the stones prior to extraction can be cost prohibitive. There is a slight loss in yield. The Integral method produces a 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: highest quality extra virgin olive oil, highly nutritious olive water, dry olive flesh for all-vegetable cattle feed, and inedible oil-bearing stones for fuel. The added benefit of this process is the elimination of processing waste which contributes to environmental degradation.