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Traditionally, olive oil, a yellow to greenish vegetable oil, was produced by crushing olives in mortars or beam presses. Modern processing involves mixing a ground olive paste with water, and extracting the oil using a centrifuge. The olive tree is native to the Mediterranean basin, where olive oil has been used for millennia as lighting fuel, anointing oil, and in food preparation. Recent scientific evidence suggests olive oil may reduce the risk of heart attacks and strokes.