Every month, I host a Q+A for some of my Patreon supporters, and a couple months ago, I was asked how to extend the shelf life of base oils for soapmaking. Since I realized I haven’t ever written about it here on Modern Soapmaking, I made a mental note to do a blog post in the future. Here we are!
Purchase Quality Base Oils in the First Place
It’s super important to purchase your base oils from reputable suppliers. One of the first questions I ask soapmakers when they have issues with their soaps developing DOS (Dreaded Orange Spots) or not turning out right is, “Where did you buy your base oils?”
A lot of oils found at grocery stores are adulterated or old (and technically, rancid.) Anne-Marie and her team over at Soap Queen did a test soapmaking session of a variety of olive oils bought in a grocery store, and the results speak for themselves.
When it comes to oils being old or rancid when you buy them, it makes sense really. From experience in the world of grocery, I can tell you that not a lot of people purchase specialty cooking oils often. A lot of those oils sit on the grocery store shelves until the expiration date, and then they’re thrown away by the store. When oils are exposed to tons of light and temperature changes, it speeds up the oxidation process, which means the shelf life of those base oils is shorter from the get-go.
If an oil is adulterated, your fatty acid profile may not be what they should be for the oils that you are using. If that’s the case, you may end up with lye heavy soap or an extra superfat, as the saponification values are not properly calculated.
Don’t waste your money on base oils found in grocery stores – usually, it’s much cheaper to purchase oils from a soapmaking supplier rather than the grocery store anyways! (Small exception: I haven’t had issues with oils purchased from local cash n’ carry, Restaurant Depot, Costco, or Sam’s Club. I think it’s because they are bulk purchasers, who tend to supply restaurants rather than consumers.)
Soaper’s Choice is the my go-to supplier for base oils online, but the smallest size they carry is a gallon (roughly 7 pounds.) If that’s too much oil for you in one go, I recommend trying general soapmaking supply vendors, such as Bramble Berry, Wholesale Supplies Plus, Nature’s Garden, etc.
Store Your Base Oils Properly
To maximize the shelf life of your base oils, you should always store them in a cool, dry, and dark place, away from heat and direct sunlight. If a base oil is especially fragile (those oils with a shorter shelf life), it’s best to keep them refrigerated, if possible.
You should keep all of your base oil containers closed tightly, and only open them when you need to. If a base oil is in a container with a lot of headspace (empty space in the container containing oxygen), you may want to consider transferring it to a smaller container to reduce the amount of oxygen exposure.
Extend the Shelf Life of Base Oils With an Antioxidant
Using an antioxidant in your base oils will help prolong the shelf life of the oil by slowing the oxidation process. Kevin Dunn wrote a white paper for the Handcrafted Soap & Cosmetics Guild back in 2005 about the effectiveness of various antioxidants and additives.
My personal go-to antioxidant is Rosemary Oleoresin Extract (commonly referred to as ROE.) I add it to my base oils as soon as I crack the seal or open the container. Some soapmakers wait to add ROE to their base oils when they are making soap, which can help prevent DOS, but it makes much more sense to me to add it as soon as possible.
Rosemary Oleoresin Extract is available with varying levels of carnosic acid (the large contributor to its effectiveness.) I personally purchase ROE with a 7% carnosic acid content, as it’s highly effective and has a much lower usage rate. The usage rate of ROE will depend on the carnosic acid content, but it’s typically extremely low at 0.5% or less.
Rosemary Oleoresin Extract is extremely thick and can be difficult to add to your base oils. To add ROE to a fresh bottle of oil, I weigh the necessary amount of Rosemary Oleoresin Extract in a clean measuring container, and then add a small amount (a couple of ounces) of oil to it. After mixing the ROE into the small portion of oil, I add the oil with ROE added, back to the main container, close the lid, and shake it up.
Side Note: If you choose to use an antioxidant or additive, please remember to include it on your product labels!
How do you know when your base oils have gone bad?
Base oils that have gone rancid typically smell bad, anywhere between stinky feet and rotten eggs. It’s quite obvious when a base oil has past its expiration date, I promise! Many suppliers will also list a shelf life and/or expiration date on the base oils they sell. If you aren’t sure, contact your supplier with the oil’s purchase date and/or batch number, and ask for a verification of the expiration date.
If any of your soaps develop DOS, which are yellow to orange spots indicating an issue with oxidative rancidity, you may have a rancid base oil on your hands. While DOS is usually caused by rancid oils, it can also be caused by high humidity or heat exposure to the soap itself, using tap water, and/or storing it with older soaps (among other issues!)