What soapmaking books print for SAP values
Makers check a calculator against the table in their book, so we checked the books. We read every saponification table in fourteen soapmaking books, from a 1908 soap-works handbook to recent ones, and set each oil’s figure beside the one the lye calculator uses, which comes from a standard, a producer’s specification or a published measurement. The books are mostly right. Where they are not, it is usually for a reason you can see.
What we found
The comparison covers 104 oils. For 68 of them the books’ figure is within 2 % of ours, and for 99 within 5 %. Of the 68 oils that more than one book prints, 52 agree within 2 %. The oil pages say which is which: each shows the books’ figure beside ours, and why they differ where they do.
19 printed figures cannot be right, across 9 oils, and are left out of the comparison: a KOH figure in the NaOH column, one oil’s row copied onto the next, or a value no fat of that make-up can have. The most repeated is palm kernel oil at 0.155–0.157 g NaOH per g, which several books print and which belongs to a fat with no lauric acid.
Of the 36 oils where the books differ from us by more than 2 %, 24 print less lye than we do. A recipe weighed to a low figure carries more superfat than it says, which is the safer mistake; a high figure takes the superfat away, and a bar made to it can come out harsher than planned.
The figures that cannot be right
- Brazil Nut Oil 2 rows
- Two soapmaking books print 0.175 g NaOH per g for Brazil nut oil, a figure that belongs to a coconut-type oil and sits just below babassu in one of them. Brazil nut oil's fatty acids put it near 193 mg KOH/g, so we use 191.6 (0.137), the measured value that agrees with them; a third book's 0.138 is right.
- Rapeseed Oil - Low Erucic Acid (Canola Oil) 3 rows
- Some books print 0.123-0.124 g NaOH per g for canola oil. That is the figure for old high-erucic rapeseed oil; canola was bred to replace it, and its lighter fatty acids put it at 182-193 mg KOH/g in the Codex standard, so we use 187.5 (0.134), as the other books do.
- Coconut Oil 1 row
- One book prints 0.118 g NaOH per g for coconut oil, against the 0.178 it gives the same oil elsewhere and every analysis of it; the standards give 246-265 mg KOH/g, and we use 256.5 (0.183).
- Macadamia Nut Oil 1 row
- One book prints 0.194 g NaOH per g for macadamia nut oil, which is its KOH figure in the NaOH column; the NaOH figure is about 0.139, as the other books print.
- Mango Butter 2 rows
- Soapmaking books print 0.134-0.145 g NaOH per g for mango butter (one prints 0.184, a slip). India's standard for mango kernel fat sets 185-198 mg KOH/g, and a stearic and oleic fat of its make-up works out at about 190, so we use 191.5 (0.137).
- Mink Oil 1 row
- Books print 0.140-0.141 g NaOH per g for mink oil (one prints 0.160, which no mink oil can take). Japan's standard for mink oil as a cosmetic ingredient sets 190-210 mg KOH/g and the oil's fatty acids come to about 198, so we use the standard's middle, 200 (0.143).
- Mutton Tallow (sheep tallow) 1 row
- The 1908 handbook prints one North American mutton tallow’s saponification equivalent as 85, where every other tallow it lists is 283.6-286. The Codex standard for edible tallow, which covers sheep fat, gives 190-202 mg KOH/g; we use 196 (0.140).
- Palm Kernel Oil 6 rows
- Several soapmaking books print 0.155-0.157 g NaOH per g for palm kernel oil, a figure for a fat with no lauric acid; palm kernel is half lauric. Malaysia's palm oil research institute surveyed its palm kernel oil and found 243-249 mg KOH/g, 245 on average, which its fatty acids confirm, and two lots analysed in 1908 took 247 and 249. We use 245 (0.175); a recipe made to the books' low figure has more superfat than it says.
- Peach Kernel Oil 2 rows
- One book prints 0.178 g NaOH per g for peach kernel oil, the same figure it gives palm kernel oil two entries earlier. Peach kernel is an oleic oil and measures 195-196.5 mg KOH/g, so we use 195.8 (0.140), close to the 0.136 other books print.
Where the books differ from us
The books’ figure is the median of one figure per book (an author’s two books that reprint one table count once), misprints left out, in g NaOH per g of oil. Largest difference first. A dot marks the oils where the books print more lye than we use, the harsher mistake. “Not reviewed” means we have not looked into that oil yet; the usual reasons are in why SAP tables differ.
| Oil | Books | Books’ figure | Ours | Difference | Why |
|---|---|---|---|---|---|
| Sea Buckthorn Pulp Oil | 1 | 0.116 | 0.135 | −14.1 % | One book prints 0.116 g NaOH per g for sea buckthorn oil. The fruit oil is mostly palmitic and palmitoleic acid, which puts it near 200 mg KOH/g, and eleven of twelve measured oils fell between 186 and 229, so we use 189 (0.135); a recipe made to the book's figure has more superfat than it says. |
| Buriti Oil | 1 | 0.149 | 0.135 | More lye than ours: +10.5 % | One book prints 0.149 g NaOH per g for buriti oil, a figure only a fat made mostly of palmitic acid could reach. Buriti is about three-quarters oleic acid and measures 189-194 mg KOH/g, so we use 189.2 (0.135). |
| Lanolin (Wool Fat) | 6 | 0.074 | 0.070 | More lye than ours: +6.5 % | Books print 0.070-0.075 g NaOH per g for lanolin, inside the pharmacopoeia's 90-105 mg KOH/g. We use the middle, 97.5 (0.070), because lanolin only partly saponifies in cold process and a higher figure would leave spare lye. |
| Inajá Kernel Oil | 1 | 0.184 | 0.174 | More lye than ours: +5.8 % | No soapmaking book we read gives inajá kernel oil a figure, and the measurements that exist disagree with each other and with the oil's fatty acids. We work it out from those fatty acids, which make it a lauric fat like babassu, at 244 mg KOH/g (0.174); one 1903 analysis found 260, so if anything this errs toward superfat. |
| Cucumber Seed Oil | 1 | 0.130 | 0.138 | −5.7 % | One book prints 0.130 g NaOH per g for cucumber seed oil. No analysis we found measures it, so we work it out from its fatty acids, mainly linoleic with palmitic and stearic, which give 193 mg KOH/g (0.138); the book's figure would need about a twentieth of the oil to be something that does not saponify. |
| Tamanu Oil | 1 | 0.148 | 0.141 | More lye than ours: +5.0 % | One book prints 0.148 g NaOH per g for tamanu oil, above every measurement we found. Tamanu's fatty acids put it near 192 mg KOH/g and its free fatty acids and resin raise measured oils to 193.5-202, so we use 197.8 (0.141). |
| Baobab Oil | 1 | 0.143 | 0.137 | More lye than ours: +4.6 % | One book prints 0.143 g NaOH per g for baobab oil, a little above every analysis we found. Measured Tanzanian oils gave 187-197 mg KOH/g and the fatty acids come to about 195, so we use 192 (0.137). |
| Rice Bran Oil | 6 | 0.129 | 0.135 | −4.5 % | Books print 0.128-0.133 g NaOH per g for rice bran oil. The Codex standard gives 180-199 mg KOH/g and India's standard for refined oil 180-195; the books sit at the bottom, where crude oil heavy in wax and oryzanol lands, so we use 189.5 (0.135). |
| Karanja Oil | 2 | 0.129 | 0.135 | −4.5 % | One book prints 0.130 g NaOH per g for karanja oil. India's standard for the oil sets 185-195 mg KOH/g and modern measured oils came in at 180-188; two 1903 analyses at 178 and 183 were of oils carrying 7-9 % unsaponifiable matter, well over the standard's 3 %. We use the standard's middle, 190 (0.135). |
| Papaya Seed Oil | 1 | 0.134 | 0.140 | −4.3 % | Not reviewed |
| Açaí Oil | 1 | 0.136 | 0.142 | −4.1 % | One book prints 0.136 g NaOH per g for açaí oil. The one measured value we found is 199 mg KOH/g and the oil's fatty acids, a quarter palmitic and half oleic, come to about 196, so we use 199 (0.142); in a recipe the difference is small. |
| Jojoba Oil | 9 | 0.069 | 0.066 | More lye than ours: +4.1 % | Books print 0.064-0.070 g NaOH per g for jojoba, all inside the producer's specification of 90-98 mg KOH/g; we use 93 (0.066). Jojoba is a liquid wax that barely saponifies in cold process, so most of it stays in the bar as superfat whatever figure is used. |
| Manketti Oil | 1 | 0.139 | 0.134 | More lye than ours: +3.7 % | Not reviewed |
| Stearic Acid (triple-pressed, ~50:50 C16/C18) | 2 | 0.143 | 0.149 | −3.7 % | Books print 0.140-0.147 g NaOH per g for stearic acid, and the difference is the grade. 0.140 is nearly pure stearic acid; the triple-pressed stearic acid soapmakers usually buy is about half palmitic acid and takes 206-212 mg KOH/g, so we use 209 (0.149). |
| Rosehip Seed Oil | 2 | 0.133 | 0.138 | −3.6 % | Books print 0.133 g NaOH per g for rosehip oil. Measured oils of both species sold as rosehip came in at 190 and 193.5 mg KOH/g, and their fatty acids agree, so we use 193.5 (0.138); in a recipe the difference is small. |
| Grapeseed Oil | 6 | 0.131 | 0.136 | −3.5 % | Books print 0.126-0.135 g NaOH per g for grapeseed oil. The Codex standard gives 188-194 mg KOH/g and the oil's fatty acids, mostly linoleic, say 192, so the lower book figures are too low; we use 191 (0.136). |
| Avocado Butter (blend) | 2 | 0.132 | 0.136 | −3.1 % | Not reviewed |
| Raspberry Seed Oil | 1 | 0.132 | 0.136 | −3.1 % | Not reviewed |
| Cherry Kernel Oil | 1 | 0.135 | 0.131 | More lye than ours: +2.9 % | Not reviewed |
| Rapeseed Oil (high erucic acid) | 4 | 0.128 | 0.124 | More lye than ours: +2.9 % | One soapmaking book prints 0.132 g NaOH per g for rapeseed oil, which is right for the low-erucic oil sold for cooking today, the same oil as canola (182-193 mg KOH/g). This record is the old high-erucic rapeseed, whose long erucic acid chains need less lye: the Codex standard gives 168-181, and we use 174.5 (0.124). If your bottle is ordinary rapeseed or canola oil, use the low-erucic record. |
| Emu Oil | 3 | 0.135 | 0.139 | −2.9 % | Soapmaking books print 0.135-0.138 g NaOH per g for emu oil. Japan's standard for emu oil as a cosmetic ingredient sets 190-200 mg KOH/g, and the oil's fatty acids, mostly oleic and palmitic, work out at 196, so we use the standard's middle, 195 (0.139). |
| Yangu Oil | 1 | 0.135 | 0.131 | More lye than ours: +2.9 % | Not reviewed |
| Perilla Seed Oil | 3 | 0.137 | 0.141 | −2.6 % | Not reviewed |
| Goose Fat | 1 | 0.135 | 0.139 | −2.6 % | Not reviewed |
| Wheat Germ Oil | 7 | 0.132 | 0.135 | −2.5 % | Books print 0.131-0.135 g NaOH per g for wheat germ oil. Japan's standard for the oil as a cosmetic ingredient sets 180-200 mg KOH/g and we use its middle, 190 (0.135). Wheat germ oil carries 4-6 % unsaponifiable matter, mostly vitamin E and sterols, which puts a typical oil nearer 185-190, where the books and two early analyses sit, so our figure may be a little high. |
| Peach Kernel Oil | 1 | 0.136 | 0.140 | −2.5 % | One book prints 0.178 g NaOH per g for peach kernel oil, the same figure it gives palm kernel oil two entries earlier. Peach kernel is an oleic oil and measures 195-196.5 mg KOH/g, so we use 195.8 (0.140), close to the 0.136 other books print. |
| Rosin | 2 | 0.128 | 0.125 | More lye than ours: +2.4 % | One soapmaking book gives rosin 12-14 % caustic soda by weight, about 0.13 g NaOH per g. Japan's standard for gum rosin sets 165-185 mg KOH/g, and US government data and a 1908 soapmaker's handbook agree, so we use the middle, 175 (0.125). Rosin varies with the pine and the grade, and some Indonesian rosin runs higher, so for more than a few percent of rosin use the figure on your supplier's certificate. |
| Blackcurrant Seed Oil | 1 | 0.134 | 0.137 | −2.4 % | Not reviewed |
| Mustardseed Oil | 3 | 0.123 | 0.125 | −2.3 % | Not reviewed |
| Almond Oil (Sweet Almond Oil) | 9 | 0.136 | 0.139 | −2.2 % | Not reviewed |
| Neatsfoot Oil | 1 | 0.136 | 0.139 | −2.2 % | Not reviewed |
| Duck Fat | 1 | 0.137 | 0.140 | −2.1 % | Not reviewed |
| Milk Fat / Ghee | 2 | 0.165 | 0.161 | More lye than ours: +2.1 % | Not reviewed |
| Oleic Acid | 1 | 0.138 | 0.140 | −2.1 % | Not reviewed |
| Watermelon Seed Oil | 1 | 0.135 | 0.138 | −2.1 % | Not reviewed |
| Medium-Chain Triglycerides (fractionated coconut oil) | 1 | 0.234 | 0.239 | −2.0 % | Not reviewed |
How this was worked out
Every row of every table was matched to an oil record by the name the book printed and converted to g NaOH per g. Each book contributes one figure per oil, the median of its rows, and an oil’s figure is the median across books. A row is left out only when it is plainly a misprint, and a chart whose NaOH and KOH columns are swapped is read the right way round. The larger disagreements were then checked against standards, producers’ specifications and each oil’s own fatty acids; where that changed our figure, the oil’s record says so, and no figure was adopted because books print it. Our side is the value the calculator uses today.
The figures papers and databases publish get the same treatment: published figures we rejected. Why honest tables still disagree is in SAP values explained, and every oil’s range and source is in the saponification chart.