The expiration date listed on a bottle of olive oil is typically two years past the date it was bottled, but two years past the harvest date is a better guideline. Opened bottles of olive oil should not be used longer than one year after the harvest date.
Olive oil goes bad through oxidation, which occurs as a result of exposure to light or air. Bottles of olive oil should be kept in a cool, dark place to avoid light exposure. The cap should be replaced quickly after use to limit air exposure. To keep unused olive oil sealed, olive oil should be purchased in several small bottles instead of fewer large bottles.
Extra virgin olive oil benefits from additional protection by adding a drop of astaxanthin, a strong antioxidant supplement, to each bottle. Astaxanthin is red, so its presence in a bottle of olive oil is visible. Once the olive oil loses the red tint, it has begun to oxidize and should be thrown out.
Because olive oil is heat-sensitive, it is further oxidized by cooking. To maximize its health benefits, olive oil should be used cold, such as in salad dressings or dips. Coconut oil, which is less heat-sensitive, can be substituted for olive oil when cooking.