True confessions here:
Early last year, I made a 20% superfat, high coconut oil soap -- I wanted to try this "break the rules" type of recipe just to see what it was all about. At trace, I split the batch and scented half with lavender EO and the other half with peppermint EO. I poured both halves into the same mold, separated temporarily by a cardboard divider, then pulled the divider. I used distilled water for the liquid. The soap was CPOP'ed and went through full gel.
By the time the bars were about 4 months old, the lavender bars were unmistakably rancid -- they turned from a translucent white to an overall rusty-yellow with a sour smell. The peppermint bars stayed very nice looking for about 4 more months, then they went bad too, although the change was slower and less dramatic. When I checked today, the lavender bar in my "bone pile" of samples is still markedly darker than the peppermint bar.
Because the ONLY difference is the fragrance, my unintentional experiment points to lavender EO as being an accelerator for the rancidity of the soap. Robert Tisserand talks about lavender EO and how it can oxidize relatively quickly -- faster than most people are aware. It's hard to know if the lavender EO I used in the soap was oxidized, but that's what I'm guessing. Lesson learned.
The other lesson learned from this soap is that I am now wary of high superfat. This is the only batch of soap I've made so far with this kind of overall, unmistakable rancidity and it's the only batch with an unusually high % of superfat. I am a scientist enough to know that one bad result is not conclusive proof of failure, but it's just not worth it to me to keep messing with high superfat recipes. I know I can make really good soap at 3-5% superfat that doesn't dry the skin, gives a refreshing wash, lasts a long time, and lathers well, so why mess with success?
Another true confession:
I made a shampoo soap over a year ago using a recipe loosely based on Genny's shampoo bar recipe. I used a stainless steel fork to texture the top of the molded soap into a "hair" like pattern. ONLY and I do mean ONLY the textured tops got a few freckles of DOS ... and ONLY on bars that were exposed to ambient light and dust and occasional handling. The bars stored in my soap storage cupboard remained 100% fine. First thought I had was that storage conditions are just as important as anything to minimize this kind of issue.
The next thought I had was to be annoyed and embarassed. Finding DOS is kind of like finding lice on your kids -- Children from "nice" families don't get lice, do they? And "good" soapers don't ever get DOS, do they? So, well, I thought, dadgumit, let's see what happens when I push the issue. I moved the freckled bars to a windowsill where they were exposed to daily direct sunlight, dust, and all that. I checked them every so often, expecting them to eventually turn totally rancid and nasty.
I got a surprise. Rather than darken or spread, the DOS freckles faded to near invisibility over time. I know the spots are there, but I doubt anyone else could find them except for the circles I scratched around the spots to mark the bad areas. The soap smells and looks fine. The common wisdom about DOS freckles is that they are a sign of inevitable overall rancidity. This experience makes me wonder about that.
