Can you use rancid oils in soapmaking?

My dear soapy friend Chrys over at Rainforest Chica recently offered donated a few kilos of rancid oils to some of our soapy friends. Why on earth would anyone want rancid oils? To make soap, of course! Read on and I’ll explain the basics of what rancid oils are, how to tell if your oils are rancid, and how to turn them into soap. For a full tutorial, with live sessions and replays check out the Soaping with Rancid and Expired Oils class!

What is rancid oil?

Fats and oils go rancid because of a process called oxidation. This happens when the fats and oils are exposed to air, light, or heat, and they start to break down (which can happen from extreme exposure, or over time). Molecules in the air called oxygen atoms can attach to the fats and change their structure (as with anything in nature). This not only makes the fats smell and taste bad, but it also can be unhealthy to eat or soap with them. If you’ve ever had soap develop mysterious orange spots later on, you’ve already seen rancidity in action—those are often dreaded orange spots (DOS) caused by oils going off in the finished bar.

Here’s a video from Chrys showing some oils that have gone rancid. It’s probably the first time I was thankful that smell-o-visions isn’t a real thing!

How to use rancid oils to make soap

Now, if your oils have already gone rancid, you might think you can’t use them at all. But there’s a special way to make soap called hot process soap where you can still use those oils! When you make hot process soap with zero percent super fat, it means you’re using just enough lye to turn all the oil into soap without any extra oil left over. This can help stop the rancid oils from causing problems in the finished soap, and saves the fats from the trash heap!

Once you have saponified all of the rancid fats into soap, you have a few options to make it worthy of being called a handmade soap (which we all know is the best soap around!):

1. Add fresh superfat
2. Salt it out

By adding fresh oils as a superfat to your hot process cook, after the rancid oils have saponified, you can add some lovely benefits to your soap without worrying about the rancid oils. Of the reasons why I love hot process soap so much! You can learn all of my tips and tricks for making hot process soap (along with more details about, fatty acids and supper fatting, and cold process soapmaking) in The Ultimate Natural Soapmaking Course.

My favorite way to use rancid oils is the second option to salt the soap out. Salting out soap involves adding a salt brine after you’ve made the soap. The salt separates the soap particles from any leftover impurities.

Once the soap is salted out, there’s so much you can do with it! I like to use my salted out soap as the base for my laundry soap., you can also create soap crumbles which are very convenient for traveling or blended up into a fresh bar of soap that floats! If you’re interested in giving it a go, you can get the full tutorial for salting out soap and my recipes for laundry soap, to-go soap crumbles, and floating soap in the Salting Out Soap Tutorial.

So, even though it’s best to use fresh oils for most things, if you end up with some that have gone rancid, you don’t have to throw them away. You can still make a clean and useful product them!

What to do next if your oils are expired or rancid

If you’ve discovered a bottle of oil that’s past its prime (or fully rancid), you’ve got options beyond the trash can:

– Double-check safety before you soap.
If an oil smells off, looks cloudy, or has separated in strange ways, assume it’s rancid and treat it that way. Don’t use it in leave-on products, and be cautious with cold process.

– Use hot process at 0% superfat.
By hot processing rancid oils with just enough lye to saponify everything, you avoid leaving any of those old oils hanging around as free superfat. After the cook, you can decide whether to add fresh superfat or move on to salting out.

– Salt it out and repurpose.
Salting out lets you separate the soap from impurities and then turn it into things like laundry soap, to-go soap crumbles, or light, floating bars. It’s one of my favorite ways to rescue “this was going to be trash” soap.

– Learn your rebatching options.
Between standard rebatch, partial rebatch, confetti/Ciaglia, and salting out, you can rescue a surprising number of “uh-oh” batches and expired-oil experiments.

– Prevent DOS before it shows up.
Even if a soap looks fine now, old or poorly stored oils can lead to dreaded orange spots (DOS) later on. Fresh oils, good storage, and mindful superfat all help reduce that risk.

Here are some resources I recommend if you’re dealing with expired oils or want to be ready for them:

• Soaping with Rancid and Expired Oils Class – full start-to-finish tutorial (also included with Best Friends Club memberships).
• Salting Out Handmade Soap Tutorial and Recipes – how to salt out and turn “meh” soap into laundry bars, crumbles, and floating soap.
• 5 Reasons to Rebatch Handmade Soap (with 4 ways to do it) – deeper dive into standard rebatch, partial rebatch, confetti, and salting out.
• DOS Soap – Dealing with Dreaded Orange Spots in Handmade Soap – what DOS is, why it happens, and how to avoid and repurpose it.
• The Ultimate Natural Soapmaking Course – if you’d like a full foundation in recipe design, superfat, and troubleshooting.

And of course, if you’d like ongoing help with “whoopsie” batches, experiments, and all the soapy science behind them, you’re always welcome to join Soapy Friends as a member and explore all of these classes together.

If you come across any rancid oils and make some amazing soaps with them, please let me know! Love to see your soapy photos and to hear more about your amazing soapy journey.