Can I add 5 % castor oil to boost the lather?

You can, and it does help a little — ricinoleic acid thickens the foam even when there is almost nothing to thicken. But it stops being castile at that point. If you want bubbles, make the bastille recipe at 72 % olive and 18 % coconut instead.

Why did my loaf stay pale and never gel?

Olive oil has no lauric or myristic acid, so the batch generates less heat on its own. Insulate it longer and set the mould somewhere warm; or accept the pale loaf, which cures to the same bar.

Does the cure really take four months?

It takes about four months to become a good bar and about six to become an excellent one. At eight weeks it is usable. If you are impatient, cut the bars smaller so more surface area is exposed, and turn them weekly.

Castile, All Sixteen Weeks of It

RRecipe card

Recipe card · 1 g
Oil	Share	SAP
Olive Oil	1 %	0.134
Oil bill	1 %	127.3

NaOH to weigh	128.6 g	NaOH @ 99 %
Water to weigh	340 g	2.67 : 1
Superfat	5 %	Lye concentration 27.2 %
Yield	9 × 163.2 g	Cure 16 weeks

Hardness17target 29–54

Bubbly0target 14–46

Conditioning82target 44–69

Reference bands follow the usual cold-process targets; the marker turns orange when a figure sits outside its band.

TTechnique notes

What 100 % olive actually scores

The gauges do not flatter this recipe. Hardness comes out at 17 against a target band of 29–54, bubbly at 0 against 14–46, and conditioning at 82 against 44–69. All three markers sit outside their bands, and the calculator will draw them in orange.

That is not the calculator being wrong. It is the honest answer to what a single-oil olive bar is: soft, almost bubbleless, and extremely conditioning. Olive oil's 69 % oleic acid is why the lather feels slippery rather than fluffy, and its near-total lack of lauric and myristic acid is why the bubbles never get big.

The chemistry of the wait

A freshly cut olive bar is roughly 12 % water by weight, held inside a crystal structure that has not finished forming. Over four months two things happen at once: the water leaves, and the soap crystallises from a soft, waxy phase into a harder one.

The second part is why a sixteen-week bar is not simply a drier four-week bar. The crystalline structure that forms slowly is denser, dissolves more slowly in the shower, and produces a finer lather. You cannot shortcut it with heat — a hot, fast gel gives you a harder bar early and a worse bar late.

When castile is worth it

For a face bar, for a baby, for anyone who reacts to coconut-heavy soap, and for a batch you make once a year and forget about. It is also the cheapest bar here — around 9 USD of oil for nine bars.

It is not the recipe for someone who wants soap next week. Make the three-oil starter bar for that, and put the castile on a shelf behind it.

Water discount, briefly

Some makers drop the water to 28 % to shorten the cure. It works, up to a point: the bar unmoulds sooner and hardens faster. It also makes the batch trace faster and increases the chance of a partial gel with a darker ring. At 34 % you get a slow, boring, reliable pour — which is what a first castile should be.

Add at trace

Nothing. Castile is the control group — adding fragrance only makes the wait feel longer

Equipment

Digital scale reading to 0.1 g
Stick blender (you will barely need it)
A shelf that you will not touch for four months

When it goes wrong

The loaf tears when you unmould it: You unmoulded too early. Olive-only soap has no lauric or myristic acid to firm it up, so it needs three to four days. Put it in the freezer for 30 minutes and it will release cleanly.
Gummy, slimy lather at four weeks: Not a fault — that is what 100 % olive soap does before it cures. Wait. If you cannot wait, add 15 % coconut next time and make a bastille instead.

MMix

Weigh 1000 g of olive oil into the bowl. If it is cold-pressed and cloudy, warm it to 40 °C and it will clear.
Weigh 340 g of water. Wearing goggles and gloves, weigh 127.3 g of NaOH and add it to the water.
Bring both to 40–45 °C. Olive oil is slow enough that you can work warmer than usual without risking a seize.
Pour the lye into the oil and stir by hand for two minutes before you touch the stick blender. Castile reaches a stable emulsion in about ninety seconds of hand stirring; you will feel the drag change.
Blend in 5-second bursts until the surface stops separating. On this recipe you want emulsion to very light trace — a thin, glossy, pourable custard.
Pour into the mould and give it three firm taps on the bench to bring bubbles up.

CCut

Cut face — Castile, All Sixteen Weeks of It — Cut face

Insulate for 48 hours. Castile often does not gel at all, which is fine — it will just be a paler, softer loaf.
Unmould at 3–4 days, not 24 hours. A 100 % olive loaf is genuinely soft for the first week and will tear if you rush it.
Cut at day 7 with a wire cutter or a very thin blade. A thick knife drags and leaves a ridge. Nine bars at roughly 118 g.

CCure

This is the whole recipe. Sixteen weeks, minimum. Stand the bars on edge, turn them every two weeks, keep them out of sunlight.
The bar you cut at week four will produce a thin, slippery, stringy lather that most people dislike. The same bar at week sixteen produces a dense, creamy, low-bubble lather that most people describe as the best soap they have used. Nothing changed but water leaving.
Weigh one bar at the start and again at week sixteen. A properly cured castile loses 10–14 % of its weight, and the bar you thought was soft at week six is rock-firm by week twelve.
Write the pour date on the label, not the sell-by date. Castile keeps for years and continues to improve through the second year.