The olives are put in a press and, umm, well, pressed and out comes the olive oil. In fact what you got is Virgin olive oil.That's all Virgin means, that it is pressed without any heating or steam or chemical extraction. The quality or 'grade' of the Virgin oil depends more on the original choice and culling of the olives than on the process used to make the oil.There are different kinds of presses from the original more primitive types still used by small "craft oil producers" (similar to the Micro-breweries and small estate vintners) to some modern high tech computer controlled machines used by the large producers. One of the simplest is just a container of some sort that the olives were dumped in, some sort of flat cover was placed in the container over the olives and stones were put on the cover and the folks went on about there business as the stones pressed out the oil. A larger vat was sometimes used with people walking around on the cover. Some snooty high cost small producers use a similar process and call it "Slow Pressed" and charge more for it. The only resemblance is in the speed of the pressing, which actually has little effect on the quality of the oil, "Slow Presses" are now mechanical or hydraulic and much larger than the old pots full of rocks . In fact they are more like the next step up in presses which are like the old time printing presses with a lever or a screw . Some smaller producers use that type and advertise as being "hand pressed" there is no difference in the oil from a similar press powered by machinery. The press that really advanced production and is still widely used today in modernized form is the stone or wheel press. A vertical wheel shaped stone on a horizontal axle connected to a vertical power shaft rolls around the bottom perimeter of a vat pressing the olives.The power shaft was powered by people, animals, wind or water. A scoop similar to a snow plow could be attached behind the wheel to lift and remove the pressed olives and new olives added behind the scoop giving a continuous process. The wheel could be adjusted so as not to press the seeds. Research indicates that the seeds are rarely pressed by the other processes and even when they are don't have much effect on the analysis of the oil anyway. Nowadays the wheel is powered by electric motors and modern "improvements" are various grooves, notches and protrusions on the wheel. You might see oils labeled "stone pressed" evoking images of "old world craftsmanship" but it doesn't mean much. Industry standards allow the use of the word "stone" to metal and synthetic "stones" powered by any source. Some producers use a press similar to a large garbage disposal with hammers that throw the olives against the walls of a cylinder . Most now use a large centrifuge that basically spins the oil out. I can add a bunch of stuff about virgin and extra virgin, fancy and light, pure and lamp oil, and probably will, but this should be enough to at leastget you started on your term paper.

I am a big fan of Olive Oil (the ingredient not the girlfirend of Pop-Eye). Some thing extra to think about is that light Olive Oil is not light in fat etc but not as good for you as Virgin or extra virgin. I heard that Light O.O is filtered/processed (heard it straight from an olive grower in Australia's Hunter Valley.

PBS just had a show on it, perhaps you could search on it to see how its' done, very interesting.