Come November, if you take a drive out into the countryside in Tuscany or the other Central Italian regions, you'll see people spreading parachutes around the olive trees and climbing up into them to strip away the ripe olives with gloved hands -- further south they also knock the olives loose with long sticks, but then again the trees are much larger, too big to make hand-stripping practical. The parachutes make it much easier to retrieve the olives that slip to the ground.
What happens next? The olives are carted off to the frantoio, or olive press, to make olive oil, Athena's great gift to humanity. Actually the word "press" is something of a misnomer -- the procedure is more complex. To begin with the olives are washed, then, if the press is traditional, they're ground in a stone trough, using upright stone wheels that were once turned by oxen and are now mechanized.
In days of old the pulp then went onto rush-mat disks that were stacked and pressed. What came out was an olive oil-and-water slurry that went into a tank to separate; the first olive oil was the best and usually went to the landlord, who used it at table. The farmers, on the other hand, used some of their olive oil at table, and the rest around the farm, to keep lamps lit and whatnot.
One of the major problems with the traditional pressing technique is its slowness: Olive oil is extremely perishable, and by the time it finishes separating in a traditional tank it has also begun to oxidize (this is why the landlord skimmed away the first olive oil, and why the farmers used much of their olive oil in lamps rather than as a condiment).
To get around this problem most modern presses use centrifuges to separate the olive oil from the water, and isolate the olive oil from the air as much as possible. There have also been advances in milling, and many presses now have continuous feed mechanical crushers. But it's still a wonderful treat to see a traditional stone wheel press rumble its way through the olive paste.
One extremely important thing about this whole procedure: It's done at room temperature. The olives are never heated, nor is the paste, and the paste is simply squeezed. No chemical treatments of any kind. Otherwise the olive oil won't be virgin or extravirgin olive oil, the two best grades. Non-virgin olive oil is either too acidic to be virgin, or is pressed from pulp that has been processed one way or another, and there is a significant difference in flavor.
Italians generally cook with virgin olive oil, and use extravirgin olive oil raw, in salads, drizzled into hearty soups, atop bruschetta, and wherever else the flavor of the oil complements the dish.
Non-virgin olive oils are acceptable for cooking, but you won't want to use one to dress your salad.
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