Obtaining the Olives
Olives grow on olive trees, where they must be harvested to begin the oil-production process. The olives can be obtained by hitting the trees to release the olives or by mechanical olive strippers that extract the olives themselves. Once the olives are obtained, they are immediately cleaned and sorted. During this process, any remaining branches or twigs are extracted from the olives and discarded, after which time the olives are placed in a cleaning machine that will remove any remaining dirt or twigs that might have made it through the initial sorter.
Turning Olives into Paste
Once clean, the olives travel to an olive mill, where they are ground and smashed down, creating a paste-like substance. This again can be done by hand or machine, though most commercial olive oil sellers use an industrial size processor because it can ground significantly more olives in the time it would take a person to manually grind them with a stone grinder or pestle. If you're attempting to make your own olive oil, however, the manual method should work just fine for small quantities.
Extracting the Oil
The olive paste is swiftly mixed, which results in the formation of drops of oil. Like all oils, these liquids will band together, rising to the top of the mixture. To expedite this process, the entire batch is pressurized, which causes the oil to separate from other liquids, including water, as well as the paste. The oil is collected in a spinning device that allows the oils to collect, while keeping out all other foreign substances. Once all the oil has been separated, it can be bottled and sold as virgin olive oil.