Technique · Salt soap
Cold Process Salt Bar
Fifty percent salt by oil weight in a 70 % coconut bill with a 15 % superfat. It has a forty-five minute cutting window, an eight week cure, and it behaves like nothing else on this site.
RBase recipe to pour into
| Oil | Share | SAP |
|---|---|---|
| Coconut Oil (76 °F) | 7 % | 0.183 |
| Olive Oil | 2 % | 0.134 |
| Castor Oil | 5 % | 0.129 |
| Shea Butter | 5 % | 0.128 |
| Oil bill | 1 % | 142.6 |
| NaOH to weigh | 144 g | NaOH @ 99 % |
|---|---|---|
| Water to weigh | 300 g | 2.1 : 1 |
| Superfat | 15 % | Lye concentration 32.2 % |
| Yield | 10 × 144.4 g | Cure 8 weeks |
Reference bands follow the usual cold-process targets; the marker turns orange when a figure sits outside its band.
TTechnique notes
Why the coconut has to be this high
Salt suppresses lather. Sodium chloride is highly soluble and it interferes with the way soap molecules organise at the surface of a bubble; in a normal bar, 5 % salt is enough to visibly flatten the foam.
So a salt bar has to fight back with the bubbliest oil in the library. At 70 % coconut the bill scores 47 on cleansing and 51 on bubbly before the salt goes in, and the salt cuts that lather roughly in half. What survives is dense, creamy and unusually stable — the sort of lather that stays on the skin rather than running off it.
Fifteen percent superfat is not a typo
A 70 % coconut bar at 5 % superfat would be harsh enough to strip the oil off your hands. Fifteen percent means a sixth of the oil bill never saponifies and stays in the bar as free oil, which is what makes a salt bar feel smooth rather than scrubby and what stops it from leaving skin tight.
It is also what stops the bar from cracking. Free oil acts as a plasticiser in a material that is otherwise a brittle salt crystal lattice.
The cutting window
A salt bar at 50 % salt is cuttable for about forty-five minutes, somewhere between the first hour and the second. Before that it is too soft and the cut faces tear; after that it is a brick and the knife goes through in ragged chunks.
Set a timer the moment you finish pouring. Check at 45 minutes by pressing the top with a finger; when the print is faint rather than deep, cut. In a warm kitchen this can be as early as 35 minutes.
Add at trace
- 500 g fine sea salt — 50 % of the oil weight, no more, no less
- 10 g lavender essential oil, optional
Equipment
- Digital scale to 0.1 g
- Stick blender
- A knife within arm's reach of the mould
- A wire rack for the cut bars
When it goes wrong
- The loaf crumbled into chunks when you tried to cut it
- You waited too long. Salt soap has a cutting window of about forty-five minutes and it starts at the ninety-minute mark, not at 24 hours. Set a timer before you pour.
- The bars are soft and bendy at two weeks
- Not enough salt, or salt that was not fine. Coarse salt dissolves slowly and leaves the bar structurally weak. 50 % of the oil weight, fine sea salt, weighed not scooped.
- There is a layer of clear liquid in the bottom of the mould
- Normal — salt bar batter releases brine as it sets. Cut on the rack rather than in the mould so the bars are not sitting in it.
MMix
- Make the base and bring it to a light trace only. Salt accelerates everything: it is a crystalline solid, it adds surface area, and a batter that is at medium trace when the salt goes in will be unpourable ten seconds later.
- Add the 500 g of salt in three lots, stirring by hand with a spatula. The batter will thicken dramatically with each lot. Do not use the blender at this stage.
- Add the lavender, if you are using it, before the last lot of salt.
- Pour into the mould immediately and press it down with the spatula rather than tapping — tapping does nothing to a batter this stiff.
- Now wait. Not 24 hours. Set a timer for 45 minutes and check the loaf by pressing the top with a finger. When it is firm enough that your finger leaves only a faint print, cut it.
- If it has already gone hard, you have missed the window and you will be cutting a brick. Salt soap at 50 % salt is genuinely rock hard within four hours and it never softens again.
CCut
- Cut at 45–90 minutes, straight down with a heavy knife, wiping the blade between every single cut. Salt soap drags and a dirty blade welds the next bar to it.
- Ten bars at about 155 g. They will be heavy — a salt bar weighs almost half again as much as a plain bar of the same volume.
- Bevel the edges immediately while the bars are still soft. An unbevelled salt bar has edges like a breeze block and it will hurt in the shower.
- Move the bars onto a wire rack straight away. They release a lot of water in the first day and sitting in that water makes the bottom faces chalky.
CCure
- Eight weeks. A salt bar needs longer than anything else here, because the salt holds a great deal of water and releases it slowly. At four weeks the bar is hard but it still sweats in a warm room; at eight it is stable.
- The bar changes character over the cure. Fresh, it is matte and slightly rough, and the lather is thin. At eight weeks it is smooth, slightly translucent at the edges, and the lather is dense and creamy — the salt has dissolved into the surface layer and the bar behaves almost like a polished stone.
- Keep salt bars out of a stream of running water. They dissolve noticeably faster than a plain bar if they are left under a tap.
What matters here
- 50 % salt by oil weight, fine sea salt, weighed. 70 % coconut to fight the lather suppression.
- 15 % superfat, held as free oil. It is what makes the bar smooth instead of scratchy.
- Cut at 45–90 minutes, not at 24 hours. Set a timer before you pour.
- Bevel while the bars are still soft or the edges will be sharp for eight weeks.
- Cure eight weeks on a rack, and keep the bars out of running water.
Questions that come up
- Can I use Himalayan pink salt?
- Yes, and the bars come out a soft pink that fades to a warm grey. The trace minerals do not harm the soap at this loading, though some people find pink salt accelerates slightly more than white.
- What about Dead Sea salt?
- No. Dead Sea salt is mostly magnesium chloride rather than sodium chloride, it is far more soluble, and it will make the bar sweat continuously and eventually turn to sludge. It is a genuinely bad idea and it is repeated all over the internet.
- Does a salt bar exfoliate?
- No. The salt dissolves into the surface of the bar during the cure, so by the time you use it there is nothing abrasive left. Salts bar are smooth. For actual exfoliation you want the coffee grounds bar.
Next on the bench
Cold-process soap is made with sodium hydroxide: goggles, gloves and ventilation, and keep the batch away from children and animals. Salt soap is soap, not a treatment for eczema, psoriasis or any skin condition, and it should not be used on broken skin.