ResolvableOwl
Notorious Lyear
If everything goes well, I'll have a crazy little project to present here in a few days. So far, I came up with this question during recipe design. Just as in NaOH-based HP for solid bar soap, it is totally possible to not add all the oils to the KOH soap batter in the beginning, but distributed over the cooking process. In general, one would gain nothing from this, since all the oils have to be saponified in the end anyway.
BUT I wonder if there is an exception to this. When the KOH purity and/or SAP value of the oil(s) are in doubt (think of self-rendered lard, or canola/sunflower frying oil blends of unknown proportions), one might prefer a mild lye discount over a lye-heavy product, to be on the safe side. However, we know that substantial amounts of unsaponified matter in LS are generally a bad idea, since they will settle at the top as an unsightly and rancidity-prone cloud layer.
When this happens, the precipitates are (obviously) less dense than water/soap solution and sufficiently hydrophobic to not stay soluble/emulsified within the bulk solution. My idea: castor oil maybe is neither. For once, it has the highest density of all oils (0.96 g/mL rather than typ. 0.92…0.94 g/mL of other vegetable oils), and ricinoleic acid has nifty extra hydroxyl groups that can bind to water (as they do with ethanol, with which the triglyceride is easily miscible), so might also act as solubilisers for partly cleaved fat molecules in aqueous solution.
So, my four closely related questions/discussion stimuli are:
tl;dr: Knowing your KOH, oils, and scales well enough to formulate a sound LS recipe in the first place is of paramount importance, and no deferral of castor oil addition will ever change this. But if, and only if those prerequisites are, for whatever reason, not fulfilled, castor oil might be an elegant loophole to control the origin and properties of unsaponified excess oils.
BUT I wonder if there is an exception to this. When the KOH purity and/or SAP value of the oil(s) are in doubt (think of self-rendered lard, or canola/sunflower frying oil blends of unknown proportions), one might prefer a mild lye discount over a lye-heavy product, to be on the safe side. However, we know that substantial amounts of unsaponified matter in LS are generally a bad idea, since they will settle at the top as an unsightly and rancidity-prone cloud layer.
When this happens, the precipitates are (obviously) less dense than water/soap solution and sufficiently hydrophobic to not stay soluble/emulsified within the bulk solution. My idea: castor oil maybe is neither. For once, it has the highest density of all oils (0.96 g/mL rather than typ. 0.92…0.94 g/mL of other vegetable oils), and ricinoleic acid has nifty extra hydroxyl groups that can bind to water (as they do with ethanol, with which the triglyceride is easily miscible), so might also act as solubilisers for partly cleaved fat molecules in aqueous solution.
So, my four closely related questions/discussion stimuli are:
- Adding castor oil late (similar to bar soap HP superfat) ensures that, if any unsaponified and/or partially reacted oil is present, it comes from castor oil, with all its implications (comparatively low risk of rancidity, less hydrophobic nature of its monoglycerides, density more similar to the bulk solution than with unsubstituted fatty acids)
- The uncertainty margin with respect to superfat (non-stoichiometric reaction) might be slightly larger with castor oil than other oils. (Don't take this as an invitation to be careless about precise maths, let alone negligent towards lye purity!).
- Unknowns remain: Impact of incomplete castor saponification on lather, reliability of the tests for completion of lye reaction, fragrances, colourants, consistency, thickening, skin safety, shelf life, microbiological safety (bug food?)
- It appears that, for the above reasons, castor oil qualifies as “first choice” to fix a LS batch that is (accidentally or intentionally) lye-heavy.
tl;dr: Knowing your KOH, oils, and scales well enough to formulate a sound LS recipe in the first place is of paramount importance, and no deferral of castor oil addition will ever change this. But if, and only if those prerequisites are, for whatever reason, not fulfilled, castor oil might be an elegant loophole to control the origin and properties of unsaponified excess oils.
