Wilted slimy lettuce, moldy fruit, and discolored vegetables are easy indicators that your produce has gone bad. It doesn't take an expiration date to tell you it's past its prime. But what about olive oil? Has that bottle on the counter been properly stored or is it in the same boat as the moldy peach in the fruit bowl? Can you trust the sell by, use by, or expired by date? Light, air, and storage temperature can affect the shelf life despite the date printed. Instead of referring to the code on the bottle, rely on your senses. Smell, sight, and taste are all you need to distinguish the good from the bad.
In testing the olive oil, the first thing to watch out for is rancidity. Olive oil contains polyphenols that break down over time. When this transformation begins to occur, the oil begins to go rancid. The best way to tell if it is rancid is simple – give it a sniff. To ensure you get the proper whiff, pour a small amount out into a bowl. The more air that reaches the oil, the better the judgment you can make. Does it smell fruity? Or is there a hint of crayon or vinegar? If it's the latter two, then it's time to ditch the bottle.
Do you know what olive oil is supposed to taste like? Off flavors can be so common in olive oil that one can easily mistake it for a determining flavor profile characteristic. Take fusty for example. Fustiness is an off flavor that occurs when the olives have begun to ferment. It can be compared to the likes of sweaty gym socks. Not exactly appealing, but many have trouble detecting it, as it is a common off flavor. Another flavor to be on the look out for is vinegar. Vinegar can have an appealing taste, but not when it comes to olive oil. The flavor of vinegar is an easy indicator that the olive oil has turned.
It may be hard to tell through a tinted green bottle, so pour a bit out into a clear glass. Has the oil changed color? Over time olive oil will lighten in appearance. As it is exposed to oxygen, the pigments lose color. When first bottled, it may have a greenish-golden color. But as the aging process occurs the color turns to a faint yellow. If you notice your olive oil no longer looks reminiscent of when you first opened it, then please, find a use for it other than cooking.