The more "saturated" an oil, the longer it will last. The more "unsaturated" or"polyunsaturated" the oil, the shorter its shelf life."
But then Javablues posted a follow up question: This question may seem silly, but when you say shelf life do you mean its good for that length of time regardless if it is on the shelf or in a product? Just wondering once a product is made with that oil, should the product be used within that shelf life time frame?"
Not a silly question at all...in fact, it's something really important to consider! The shelf life of an oil is more than just the life it has on the shelf before it goes into your soap. It has a life before it gets to you...and then it has a life once it gets made into soap.
So the answer is yes to both considerations...sort of...
Definitely "shelf life" applies to the time it spends on your shelf - and there are things you can do to lengthen the effective shelf life:
- Make sure you buy your oils from a quality vendor - you want to make sure that the oils that you're buying are fresh...that they haven't used up part of their shelf life on the vendor's shelf!
- Once you get them, store them in a cool, dark place
- As you use them, put them in the smallest bottle possible. It's contact with the air (the oxygen) that oxidizes the oils and makes them go rancid. If there's no contact with air, the oxidation is much slower. So as you use it, either pour the oil into a smaller bottle, or what I often do is squeeze the bottle so that all of the air is squeezed out, and then put the cap on.
- You can also add an antioxidant like rosemary oleoresin (ROE) (my preference) or vitamin E. I add it to the whole bottle of oil when I first get it. It greatly extends the shelf life of the oil.
SO...that was the first part of your question...now to the second part...
All of that applies to the raw oil...does it apply to soap?
Sort of...it doesn't really apply to the "soap" part of the soap - that will last for a long, long time. But it does apply to the "superfat" part of the soap...the free oils that have been leftover in the soap by superfatting. It's those oils that will go rancid and make the soap go bad. Most soap makers believe that it's those free oils that contribute to DOS (dreaded orange spots) too.
Now let's say that you've used 10% grape seed oil (a short shelf-life oil) in your soap recipe...and superfatted at 5%. That would mean that the soap would have .5% grape seed oil leftover in it as part of the superfat. (10% X 5%) That's not a lot...and shouldn't cause much problem...at least for a year or so...and would be even less of an issue if you added some ROE to the oil when you first got it from the vendor.
But if you were using the oil in a lotion or balm...you have a much much higher % of the oil left intact, so the freshness of the oil, and its shelf life is much more important to consider.
Learn more about the qualities of soap making oils.
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