episode 1 >> MILLING
When most people think about making olive oil, they often still imagine a donkey pulling a stone wheel around. This romantic notion, however, often misleads them in thinking that the old-fashion way of milling olives is the best way. This is one of the great myths about olive oil.
“First press” is no longer an official definition for olive oil. A century ago, oil was pressed in screw or hydraulic presses. The paste was subjected to increasingly high pressures with subsequent degradation in the flavor of the oil. Today the vast majority of oil is made in continuous centrifugal presses. There is no second pressing.
“Cold pressed” is an anachronistic and largely unregulated label description for olive oil. Fifty years ago when most oil was made in vertical presses, the paste was pressed to make olive oil (first press) and then mixed with hot water or steam and pressed again to remove more oil. This “second pressing” was not as good; the heat had evaporated some of the delicate flavors. Today the paste is almost always warmed to room temperature during the malaxation process before being centrifuged using horizontal decanters (Olives are harvested in the winter when it is cold). According to IOOC regulations this is still considered “cold pressed”. Heating the paste excessively increases yield but degrades flavor.
Regulation 1019 of 2002 determines the use of the term “Cold Pressed” in the EU. During Malaxation and Extraction the olive paste must be kept under 27ºC (81ºF).
Modern equipment, although it does not have the aesthetic appeal of the old stones and presses, allows producers to make vastly superior and healthier oil at a lower price, in much more sanitary conditions.
The basic steps in making olive oil are always the same, no matter what kind of equipment is used.
- 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.
- 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.
- 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.