In many Lê Mai soaps that contain sweet almond oil, it is the only oil whose share is given as a number. The product descriptions say it makes up more than 30 percent, above 30 percent, or about 30 percent of the formula. It is a liquid oil, almost odourless, rich in oleic acid and with a noticeable share of linoleic. This piece starts from its fatty acid table to see what the oil does in the lye pot, in the finished bar, and in the months after the bar leaves the curing rack.
An oil pressed from a kernel, not an essential oil
Sweet almond oil is pressed from the kernels of Prunus dulcis. The library places it among the fixed oils: oils that do not evaporate and carry triglycerides, fatty acids, fat soluble vitamins and phytosterols. The vegetable oils page calls it the most common carrier oil, balanced, moderately absorbed, high in oleic, with vitamins E and A.
The name is easy to confuse. The library also has a page for bitter almond essential oil, distilled from the kernels of Prunus dulcis var. amara, with benzaldehyde at 98 percent or more. Benzaldehyde is the familiar almond scent of pastries. The sweet almond oil used in soap carries almost none of that scent, because it is the fat of the kernel, not its volatile part.
Because it carries no scent, sweet almond oil does not change the fragrance of a bar. Its role lies elsewhere: it decides a large part of the fatty acids that enter saponification, and through them the lather, the hardness and the durability of the bar.
The fatty acid table: oleic first, linoleic second
The fatty acid table in the library gives sweet almond oil 60 to 78 percent oleic, 17 to 25 percent linoleic and 6 to 10 percent saturated fatty acids. These are approximate figures, because each harvest, variety and pressing gives a slightly different oil.
Oleic is an 18 carbon fatty acid with one double bond, in the omega-9 group. Linoleic also has 18 carbons but carries two double bonds, in the omega-6 group. Saturated fatty acids such as palmitic and stearic have none. The library notes that this count of double bonds is what makes the difference: saturated fatty acids give an oil a thick or solid texture at room temperature, unsaturated ones keep it liquid.
Set beside extra virgin olive oil in the same table, the closeness is clear. Olive has 65 to 80 percent oleic, nearly the same range as almond. The difference lies in the other two columns: olive has only 5 to 15 percent linoleic, but 14 to 18 percent saturated. Almond has more linoleic and fewer saturated fatty acids.
A Castile bar uses olive oil alone, so nearly all of its character comes from the oleic column. When almond replaces part of the olive, the oleic column stays almost the same, while linoleic rises and the saturated share falls. Those two small shifts explain most of what can be felt in the bar.
In the lye pot
Saponification is the reaction in which NaOH cleaves triglycerides into glycerin and the sodium salts of fatty acids. With almond oil, the product is mainly sodium oleate, with some sodium linoleate and a little sodium palmitate and sodium stearate. Each of these salts is a soap molecule: one end dissolves in water, a long carbon tail dissolves in oil.
The amount of NaOH needed per gram of oil, the SAP value, depends on the average length of the fatty acids. The library records that coconut oil needs about 0.190 grams of NaOH per gram because lauric is short, while olive needs about 0.135 because oleic is long. The main fatty acids of almond are 18 carbons long, like those of olive, so its alkali requirement sits near olive and far from coconut. Even so, each batch is calculated from the SAP of each oil, to the gram, as the six week piece describes.
Almond is liquid at room temperature, so it does not need to be melted separately like cocoa butter or shea butter. It joins the oil phase already warmed to 38 to 40°C and then meets the lye solution at the same temperature. The library notes that olive is slow to trace; soap makers also commonly note that an oleic rich base needs longer stirring than a base heavy in coconut or saturated fats.
A fine lather and a softer bar
Each fatty acid salt gives its own kind of lather. The library records that the lauric of coconut oil produces strong lather when saponified, that coconut and palm give bubbly lather and hard bars, and that olive gives a soft, conditioning bar. Sodium oleate dissolves in cool water more readily than the salts of saturated chains, but it does not make many large bubbles. Soap makers note that an oleate rich bar gives small, dense bubbles rather than large airy ones.
Almond oil follows olive because both are rich in oleic. Its higher linoleic and lower saturated share make the bar a little softer than an olive bar at the same proportion. A chain with a double bond is bent, so the soap molecules cannot pack as tightly as straight saturated chains, and the block of soap is less firm.
This is why almond oil rarely stands alone. Lê Mai's Bitter Melon Artisanal Soap No.094 has 14 ingredients, led by more than 30 percent sweet almond oil, with cocoa butter, neem seed oil and spirulina, along with bitter melon powder and concentrated bitter melon juice. The library records cocoa butter at 57 to 64 percent saturated fatty acids; in a formula like this, it is the saturated fat standing beside a soft oil base.
Linoleic and oxidative stability
A double bond is where oxygen attacks. The library records that linolenic, with three double bonds, goes rancid fastest, linoleic with two is moderate, oleic with one is slow, and oils rich in saturated fatty acids such as coconut, cocoa and shea stay stable longest. The shelf life table on the same page gives sweet almond about one year, olive one to two years, coconut two to four years and cocoa butter two to five years.
Saponification does not remove double bonds: sodium linoleate keeps the two double bonds of its parent acid. In addition, a formula usually leaves 5 to 8 percent of the oil unreacted, the part the library calls superfat. If that excess is rich in linoleic, it is one of the parts of the bar most prone to oxidation in the months that follow.
A small calculation shows the scale. Taking only the almond part at 30 percent of total oils, with the library's ranges, it contributes about 18 to 23 percent oleic and about 5 to 7.5 percent linoleic to the formula. At that level, linoleic is still a small part of the total. A bar made almost entirely of almond would have more than three times as much linoleic.
Vitamin E, or tocopherol, is a natural antioxidant present in many oils, as the library notes, and sweet almond oil is one of them. How a bar ages is the subject of another piece; here it is enough to note that the linoleic level of the whole formula is one of the numbers that decide that durability.
Three bars on the same almond base
For the three bars in this piece, the product descriptions give the almond share in two ways: above 30 percent for Bitter Melon and Green Tea, about 30 percent for Ricard 1932. It is the only share in the formula given as a number; the other oils and butters are only named.
Green Tea and Dead Sea Salt Artisanal Soap No.107 has 14 ingredients, with almond oil above 30 percent, Japanese matcha, concentrated green tea and Dead Sea salt. The oil base here is soft and rich in oleic. The salt is a mineral salt, not cleaved by NaOH the way triglycerides are; it stays in the block of soap together with the tea powder.
Ricard 1932 Artisanal Soap No.018 has 13 ingredients, about 30 percent almond oil, with cocoa butter, shea butter and tamanu oil, scented with star anise essential oil, Illicium verum, and star anise powder. Here two solid fats stand beside the almond oil. The library table gives shea butter 42 to 50 percent saturated fatty acids and cocoa butter 57 to 64 percent.
Side by side, the three bars show the same construction: a liquid, oleic rich oil makes up most of the base, giving a fine lather and a soft bar; a few saturated fats stand beside it to hold the bar's shape. At about a third, almond is enough to set the voice of the lather, while the linoleic share of the whole formula stays small. The exact share of each remaining fat is not given in the descriptions, so this piece stops at that structure.
Sweet almond oil brings no scent to the bar. It brings fatty acids.
Oleic gives a fine lather, linoleic makes the bar softer and is the part to watch for oxidation.
About a third of the formula, enough to set the voice of the bar while leaving room for saturated fats.