Olive oils naturally degrade over time, and olive oil that's past its prime will lose healthy antioxidants and eventually go rancid.
The most important thing you can do to prevent this from happening is to store your olive oil properly. Most olive oils stored properly in the original sealed packaging have a shelf life of 1½ to 2 years and once you open the bottle you should use the oil within a few months.
Olive oils have three main enemies - heat, light, and air. Avoid these conditions to preserve the quality and extend the shelf life of your olive oils:
Heat speeds up the breakdown of the oil, so don't store it near the stovetop, on top of the refrigerator, or anywhere in your kitchen where heat will collect
Light, especially direct sunlight or fluorescent light, also accelerates the breakdown of the oil. As tempting as it is to display a pretty bottle in the shop window, don't do it!
Increased exposure to air causes the oil's antioxidants to be depleted. That's why you should use up opened bottles - every time you pour some oil out, more air stays in the bottle. Don't make a vent hole in the top of cans for the same reason - while it might be easier to pour if you can't reseal it, it will
Oil now being in constant contact with air - a big no. no
The same goes for pourers without a lid – you want to be able to cap or seal your bottle after each use.
After all, people often ask about refrigerating olive oil. If the oil is exposed to extreme cold during shipping or storage, it should still be good when it returns to room temperature. However, some research suggests that repeated heating and cooling -- like storing it in the fridge between uses -- puts a lot of stress on the oil and doesn't necessarily extend its shelf life. Storing your olive oil in a cool, dark cupboard or pantry is the way to go!