ResolvableOwl
Notorious Lyear
ETA tl;dr: From several points of view, it appears that staying well below 15% of linoleic acid is a reasonable rule of thumb. Exceeding it should better be the exception for those who know what they're doing, first of all how to guard against rancidity/DOS. That said, linoleic acid is a worthy component of soaps, and fun to explore!
I didn't want to strain the grocery store challenge thread more with this topic. FWIW, the complicated relationship of soapmaking with poly-unsaturated fatty acids (PUFA, mainly linoleic acid) deserves its own thread!
The situation (largely stolen from my reply over there)
Regarding to PUFAs implying an application maximum, non-lauric oils fall into roughly three categories:
Contra High-linoleic
Pro High-linoleic
A list of thoughts that came upon me on maxing out linoleic – while still roughly staying within the limits of proven bar soap recipes (hardness/longevity number). Crazy things like pure HL sunflower soap are not meant, if at all, they deserve another thread.
Currently, my personal approach is to max out the 15% “linoleic budget”, as long as the rest of the recipe allows for it (looking at you, longevity number!). Replacing olive/HO sunflower by rice bran oil is a nice and easy way to do so.
“Luxury” oils like hemp, oat, poppy at low single-digit percentages appears like a waste of effort (or a mere PR gag/green labelling) to me. If these oils are really so great, why not add 10% or 15% of them?
High-linoleic and mid-linoleic oils appear somewhat mutually exclusive: they compete for the same limited “resource”: the reserves of permanent self-protection of a soap bar against rancidity.
Also, my mention of the 60% canola oil in the grocery store challenge didn't come out of the blue (without being too suggestive at this point). The hard part is to explain to my “former self” why, back then, it was a Bad Idea™ to flood a soap recipe with 60% canola, but now it is okay?!
I didn't want to strain the grocery store challenge thread more with this topic. FWIW, the complicated relationship of soapmaking with poly-unsaturated fatty acids (PUFA, mainly linoleic acid) deserves its own thread!
The situation (largely stolen from my reply over there)
Regarding to PUFAs implying an application maximum, non-lauric oils fall into roughly three categories:
- Classic base oils: olive, HO seed oils, hard oils, lard… (without quantity limit)
- “Luxury” oils with high iodine value: HL sunflower, safflower, sesame, hemp, poppy, flaxseed, fish oil… (very prone to rancidity, usually added in small quantities, if at all)
- In between (15…30% PUFA): canola, rice bran, peanut, almond and a few others. Provided a robust recipe, proper curing/storage, and chemical precautions (ROE, chelators), these can still make up for a major fraction of the oils.
Contra High-linoleic
- Respect towards time-proven rules of recipe design (classic trinity, max iodine value, min INS, min hardness, max PUFA) is a (comparatively) easy and reasonably reliable way to stay happy with one's soap in the long run (over years). Undoubted authorities with a lot of experience in the field have wrapped up their experiences in recommendations. Those are no natural laws (in the strict sense), but still it'd be silly to violate against them for short-term effect. Inconvincible, just to find out, after a long journey of long-term frustrations, that reinventing the wheel wouldn't have been necessary if one stuck to old-fashioned wisdom in the first place. Being adventurous is okay, but it is self-deception to conceal laziness or stinginess under a healty degree of skeptic insubordination.
- Lye discount/superfat allegedly amplifies the rancidity issues with high-PUFA soaps, Low-PUFA recipes allow for a larger margin of error. The interval between lye-heavy, harsh soaps and detrimental superfat shrinks with increasing PUFA contents. And this is not necessarily in the hands of soapmakers themselves (inevitable natural variations).
- My own experience with linoleic oils and hardness (or the lack thereof) is that oleic and linoleic acid initially behave similarly in the soap batter (fluidity, trace speed, temperatures), but linoleic lacks the “castile kick” for hardening, i. e. it complicates unmoulding, and (more importantly) it won't contribute to (or even impede) a hard bar even after a very long curing time (months and longer).
- “Castile slime” apparently is a property of unsaturated fatty acids in general, not just oleic acid. Linoleic acid probably contributes to it, but definitely won't prevent it. Just now, I have tested a two months old 100% cottonseed oil soap (ca. 80% unsaturated with L:O 3:1) that has hardened up lovely, but once wet, it becomes just as ropy and slimy as a high-oleic castile soap.
- When you observe well-founded rules like <15% PUFA, longevity number >25, coconut <20%, it is impressive how this magically ensures INS>130 and IV<70 (as if someone clever had thought through this?). As soon as you drop the <15% PUFA rule, it becomes a lot easier to come up with a very questionable soap recipe. Not that I'm accidentally becoming an INS disciple, but its strict and easy limits keeps unwelcome surprises away. I wonder if there are soap calculators out there that emphasise a “PUFA number” with the respective limits?
Pro High-linoleic
A list of thoughts that came upon me on maxing out linoleic – while still roughly staying within the limits of proven bar soap recipes (hardness/longevity number). Crazy things like pure HL sunflower soap are not meant, if at all, they deserve another thread.
- Availability: It is more comfortable for beginners and small-size/opportunity soapers to branch off some kitchen ingredients, than to hoard oils dedicated to soapmaking. Canola and/or peanut/rice bran oil are dead cheap in many parts of the world and easy to restock in case you run out of supply. Including mid-linoleic oils broadens the palette to express your opinions about global flow of goods vs. regionality, GMO, animal products, organic agriculture, “food or fuel” (inedible rapeseed, jatropha!) etc.
- The unique texture of linoleic soaps. Some observations: They are silky, slightly translucent, and have a glossy surface. They stay a bit gummy and are still a bit pliable after a long time, and by no means brittle. Comparable high-oleic recipes have been a bit chalky in my experience, and much more prone to soda ash.
- (My) skin loves PUFA lather. It feels super soft and gentle, yet cleans well, and washes away easily. The skin feels soft, dry and clean afterwards, without feeling stripped off or tight. And it appears to be less sensitive to hard water to build up soap scum.
- Rancidity can be delayed/slowed down by addition of antioxidants (ROE) and chelators. A clever idea in any case. With proper precautions, it is probably possible to reach linoleic content significantly above 15% without DOS attacks. Someone just would have jump in and find out how far one can push this limit – an unthankful, time- and patience-consuming business…
Currently, my personal approach is to max out the 15% “linoleic budget”, as long as the rest of the recipe allows for it (looking at you, longevity number!). Replacing olive/HO sunflower by rice bran oil is a nice and easy way to do so.
“Luxury” oils like hemp, oat, poppy at low single-digit percentages appears like a waste of effort (or a mere PR gag/green labelling) to me. If these oils are really so great, why not add 10% or 15% of them?
High-linoleic and mid-linoleic oils appear somewhat mutually exclusive: they compete for the same limited “resource”: the reserves of permanent self-protection of a soap bar against rancidity.
Also, my mention of the 60% canola oil in the grocery store challenge didn't come out of the blue (without being too suggestive at this point). The hard part is to explain to my “former self” why, back then, it was a Bad Idea™ to flood a soap recipe with 60% canola, but now it is okay?!
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