Soap going bad?

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New Member
Jan 18, 2011
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Hello :)
I have this odd problem of my soap going bad. I don't understand how some cure their castile soaps for 6 - 12 months... My soap starts to go rancid at about the 3 month mark.
The surface turns yellow & it starts to smell like rancid oil.
I mainly use 90% olive & sunflower, with 10% coconut, cocoa & candelila wax for hardness.
Reverse osmosis water
7% superfat
essential oils - no fragrance oil
hot process & CPOP

Thank you so much for your help!
Your problem may be the sunflower oil. Pure Castile soap is made with 100% olive oil. After a cure of several months pure Castile soap will be hard with good, creamy lather.
You may want to try Zany's No Slime Castile. It's a game-changer for castile (and other olive-based soaps) soapmakers. Take some time to read through the thread to get a feel for making it. It comes together fairly quickly. You can unmold and cut within hours of making it. I start using it at the 2-week mark, although the longer the cure, the better the soap. :)

Here's a video of ZNSC that someone posted on YouTube. Be sure to make a small 16 oz. / 500g batch exactly as written before tweaking it. In the video, she doesn't use the recommended temp of 35°C - 40°C (100°F - 110°F) and it's slow to trace. The rest is well done.

Your problem may be the sunflower oil.
:thumbs: I agree. Skip the sunflower, cocoa & candelila wax for hardness. The Faux Sea Water helps with the hardness. Try 100% Olive Oil, 0% SF (to reduce the slime castile soaps are know for) or my favorite combo for better lather and hardness: 85% olive, 10% coconut 76°, 5% castor. 😉
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What is the brand of olive oil you're using?(lots of brands are adulterated with cheap oils) What is the brand of sunflower (and is it high oleic?). OR...does the oil come already blended in a single bottle?

How old are the oils, and how are they being stored? Where are the bars being cured and are they exposed to humid air, sunlight, dust? Is air able to circulate around them? (whew, lots of questions, sorry!). When was the last time you changed the filter in the R/O?

In general, I'd consider lowering the superfat to 3 or 4% if your coconut percentage is low. That will reduce the amount of unsaponified oil floating around in the bar that tries to go rancid. If you have fresh, high oleic sunflower I see no reason to stop using. It's one of my favorite oils to use (under 20%) and I use a lot of it without having rancidity issues.