Oil Stability by Fatty Acid Type

The most stable oils are the saturated butters that are solid at room temperature – because the carbon atoms are saturated with hydrogen, there are fewer places for oxygen to attach and cause the oil to oxidize.

Next are monounsaturated oils like olive, almond or avocado. Most of the oils that are dominant monounsaturated fatty acids will last up to a year and usually much more when you control the environment they are stored in.

Oils high in polyunsaturated fatty acids are the most susceptible to rancidity. It is especially important to protect polyunsaturated oils from heat, light and air.

And finally, the very long chain fatty acids of 20 carbons and longer, have a unique ability to help protect other oils in a formula.

Exceptions to the Rule

There are exceptions to the fatty acid type rules however. Polyunsaturated oils that contain high amounts of antioxidants hold up better than those polyunsaturated oils lacking them.

Antioxidant compounds help prevent oxidation in oils and so they last longer than one might expect on first glance.

For example, raspberry seed oil is so loaded with antioxidants that the oil has a relatively long shelf life; up to a year even though it is close to 75% polyunsaturated fatty acids.