Shelf life varies a lot with carrier oils so I want to take a few minutes today to discuss why this happens and how to work with the oils so that they stay fresh as long as possible.
The four factors that impact the shelf life of carrier oils are time, temperature, light, and air. Control as many of these four factors as possible, and you can extend the shelf life of your oils.
First, let’s look at carrier oils most prone to going off rapidly. These are the oils high in polyunsaturated fatty acids, like grapeseed oil or evening primrose, hemp, and flax.
Why do oil high in polyunsaturated oils go off more quickly than other carriers?
Polyunsaturated oils have places on the carbon chain where hydrogen atoms are absent and oxygen can attach. And, when oxygen attaches to the chain, it oxidizes, causing the oils to become rancid. As oil oxidizes, it will start to smell off, and eventually, the oil will begin to dry.
Store oils in a cool, dark place. This is good practice for all oils but is especially important for the polyunsaturated dominant oils. Brown bottles also help keep light out which can help extend shelf life. These oils typically have a shelf life of six to 18 months with careful handling.
Here are a few more examples of polyunsaturated oils:
- rosehip seed oil
- walnut oil
- safflower oil
- soy oil
- borage seed oil
- black currant seed oil
- kiwi seed oil
Heating polyunsaturated oils safely
But, what about making salves with polyunsaturated oils? There is no single temperature that turns an oil rancid. Rather it is heat and light over time as well as exposure to the air that causes oxidation and eventually rancidity. When working with the oils to make salves, keep the time that they are heated as short as possible. Start a salve by melting waxes and any butters and other saturated oils, then add the polyunsaturated oils last so they don’t get overly heated.
What about oil that is a year old with a one-year shelf life? If it has been stored in a cool cupboard and never opened it is most likely fine. An exception would be hemp or flax which need to be refrigerated. Unopened oils that haven’t been exposed to air (oxygen) will hold up longer than opened oils.
Saturated oils & stability
The most stable oils are the saturated oils – these are the butters that are solid at room temperature – because they have more hydrogen attached to their carbon chains and so fewer places for oxygen to attach.
Monounsaturated oils and shelf life
Somewhere between saturated oils and polyunsaturated oils are carrier oils dominant in monounsaturated fatty acids. These don’t need refrigeration but cool, dark storage is essential. Monounsaturated oils last 12 to 18 months or longer depending on the type, storage method and other factors.
Monounsaturated oils are your olive oils, almond oil, avocado and others.
Tips for prolonging shelf life of a recipe or formula
Adding a few drops of vitamin E extract to your formulas will help preserve the oils. Vitamin E is an antioxidant that acts as a natural preservative by slowing oxidation.
Or you can add meadowfoam seed oil. Meadowfoam seed oil is liquid at room temperature – meaning it is unsaturated – but it has an exceptionally long fatty acid chain and can naturally extend the shelf life of other oils in a blend. So if you are using a lot of grapeseed oil, rosehip seed oil, and other less stable oils, add some meadowfoam oil to your blend to stabilize it.
A lot of variables
While dominant fatty acids give us some indication as to the shelf life of a specific carrier oil, there are a lot of variables. I’ve noticed that raspberry seed oil, despite being high in polyunsaturated fatty acids, holds up well over time. But then raspberry seed oil is high in anti-oxidants so it would make sense that those are protecting the oil to some degree.
What carrier oils are you working with and loving right now? Leave a comment below and share your thoughts.