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(遠心分離機). The olive tree is native to the Mediterranean basin(流域), where olive oil has been used for millennia(何千年)as lighting fuel, anointing(油を塗る)oil, and in food preparation. Recent scientific evidence suggests olive oil may reduce the risk of heart attacks and strokes.