How should I store oils?

Heat, light and oxygen degrade oils, which makes them turn rancid more quickly and actually promotes the formation of cancer-causing compounds called free radicals. The more polyunsaturated fats an oil contains, the more susceptible to rancidity it becomes.

Oils rich in PUFAs, such as walnut and flaxseed, are best stored in the fridge in tightly capped containers. MUFAs, such as those found in olive oil, are a bit more hardy, but you should still protect oils that contain them by keeping the lid on tightly and storing them in a dark place far from the stove or other heat source. Saturated fats, such as butter, can withstand more heat, light and oxygen, but you should still refrigerate sat-fat–rich butter, because it contains milk solids, which can go rancid. If you store oils correctly, most will last about six months to one year.

When you’re shopping for oils, reach for bottles at the back of the shelf, since that’s where they are more protected from harsh lighting that can make them go bad. Check the bottle for an expiration date (most oils have one), and every time you open a bottle, give it a whiff to make sure it doesn’t smell rancid.


Source