Rancid 25% Brine Soap (but other batch perfect)

[Garden Gives Me Joy]

I made tiny batches of 1 or 2 small test bars. In total, I did 6 iterations; two 25% brine (and four 60% crystalline), all using oils from the same bottles. All done within a 24-hour period. Both brine soaps were done within 2 hours of each other. However, one iteration (#2 below) reeks of rancidity ... and gave me my first DOS experience within only 7 days of pouring. All the crystalline bars (using the same ingredients at different proportions) are fine.

My methodology: To do both brine soaps, I dissolved the salt in water that was still boiling hot. After the water cooled, I added the NaOH. Strained the lye water into the oils, stick blended and then molded immediately afterwards. Neither had fragrance oils. #2 was not as smooth looking as #1 when I poured it.

Results so far: After 2 weeks, #1 is perfectly white (without DOS) and no scent at all. As to be expected, #1 is harder. Unfortunately, the rancid soap (#2) feels so much nicer than its otherwise perfect (#1) counterpart. I suspect the presence of the castor oil in #2 explains the nicer feeling.

25% Brine Soap #1 - not rancid (see recipe with green circle)
I forgot to add the castor oil (and thus the reason for iteration #2 below)

25% Brine Soap #2 - rancid but lovelier feeling than #1

What went wrong?

1. Had I accidentally poured an excess of sunflower oil, thereby creating a superfat that far exceeded my intended 11%? My understanding is that sunflower is notorious for creating DOS because of its high content of linoleic fatty acid.
2. Had I accidentally used too little water thereby creating a water discount that can cause problems? I remember finding it odd that the salt did not dissolve as readily as the first iteration, even though the water was hot in both cases. Unlike the first iteration, there were crystals left back in the strainer.
3. Could the culprit be the only oil that is not in #1, my beloved, castor oil? Someone else suspected castor oil in an earlier post. However, all 60% salt crystalline bars have castor oil and are fine. .. the higher salt content is preserving? ... but other batches made 1 month before with the same bottle of castor oil are still fine.
4. If I formulated this badly, how might I improve the recipe to prevent the likelihood of repeating the rancidity please? ... or are there certain special methodology precautions I might have missed in the rancid batch? (I was tired and annoyed about having to redo the brine soap). Could I have poured before allowing saponification to occur properly?
5. If an explanation you might have seems in reverse for some reason, the labels blew off the counter and, although I believe I have re-labelled the 2 soaps correctly; who knows!
6. Should I consider using citric acid as a type of preservative as a preventative measure? However, I'm unsure how much to use. Someone online suggested adding 6g NaOH for every 10g citric acid. If this is sound advice, how much citric acid should I use?

One contributer in that old thread spoke about using brine to correct rancidity in non-brine soap. The science went over my head. However, I thought that the salt should have protected my soap better than otherwise.

 

[AliOop]

Your #1 and #2 options seem like viable possibilities to me.

More importantly, both recipes include more than double the amount linoleic + linolenic acids. That combined number is typically 15 or less to avoid DOS or other rancidity; your recipes are at 39 and 37, respectively.

I don't believe citric acid is going to fix that, as my understanding is that CA is used as a chelator to prevent soap scum, not as a preservative.

 

[shunt2011]

If you're not using HO Sunflower that is likely the culprit for the DOS. Are you using distilled water? CA is a chelator not a preservative. Here' some great information for your reading pleasure. Soapy Stuff: Soapy Stuff