The label Most American markets carry two types of olive oil, one labeled Pure and one labeled Extra-Virgin. Pure olive oil is produced from bruised or otherwise defective olives;the oil is then stripped of unacceptable aromas and flavors. Extra-virgin oil is produced by crushing healthy olives as quickly as possible after harvest--within 24 to 48 hours--to retain the olives' complex flavors.
The flavors Extra-virgin oil should have a balance of flavors that are fruity, bitter and pungent--the back-of-the-throat pepperiness characteristic of oil from fresh olives. Like fine estate wines, the best oils vary considerably in flavor. You may prefer one oil for salads, another for sautés and a third to garnish a delicate fish. I keep at least three or four on hand at any given time.
The olives Olives may be picked at all stages of ripeness, with colors from thoroughly green to green streaked with amethyst to the rich, glossy black of mature olives. In general, the younger the olives at harvest, the more the oil will exhibit a pleasing roughness, with mature olives giving a smoother, sweeter oil.
The shelf-life Properly stored in a cool, dark place, fine extra-virgin oils should be good for up to two years.