How to Make Lavender Soap (and What the Lye Taught Me)

I started making soap for the least romantic reason available, which is that we had too much lavender and I am constitutionally unable to throw away anything that grew on purpose. There is a low stone wall behind the house that the lavender has decided belongs to it, and every June it produces roughly nine times more than a household can use, and every June I stand in front of it thinking: someone should do something about this.

That someone was me, and it took four batches before I produced anything a reasonable person would put on their body.

What follows is the recipe that finally worked, which I will give you properly and in full, because most soap recipes on the internet are written by people who have never had a batch fail and it shows. But first, briefly, the four failures, because they contain all the actual information.

The four batches

Batch one: the scrambled eggs

I had watched perhaps eleven videos. In all of them a calm person poured a smooth liquid into a mould and it stayed smooth. Mine went, in under four seconds, from a pleasant custard to something with the exact texture and dignity of scrambled eggs left in a pan.

This is called seizing. It happens when the mixture solidifies almost instantly, and the usual culprits are working too hot or adding fragrance too fast. I had done both. I had also, I later realised, dumped the entire measure of essential oil in at once and then run the stick blender through it, which is roughly the soap equivalent of revving an engine with no oil in it.

I spooned the eggs into the mould anyway, because I refused to accept it, and four weeks later I had a loaf of soap with the internal structure of a dry scone. It washed. It just looked like something recovered from a wreck.

Batch two: the volume incident

In batch two I measured the lye by volume. In a cup. Like flour.

I want to be very clear about how wrong this is, because it is the one mistake in this entire article that can actually hurt you. Soap is a chemical reaction with a fixed ratio. Every single ingredient must be weighed on a digital scale. Sodium hydroxide in flake form and sodium hydroxide in bead form occupy completely different volumes for the same mass. A cup is not a unit. A cup is a guess wearing a costume.

The result was lye-heavy soap: too much caustic, not enough oil to react with it. It looked fine. It was not fine. It was a bar of soap that would take a layer of you with it. I zap-tested it — touching a wet bar briefly to the tongue, which gives you an unmistakable battery-terminal jolt if there is free lye present — and got the jolt, and threw the entire loaf away, and felt sorry for myself for a day and a half.

Batch three: soap on a stick

Batch three thickened correctly and then kept thickening, past pourable, past spoonable, into a state where it welded itself to the stick blender and I was left holding a piece of kitchen equipment inside a solid mass of soap, in the manner of a sword in a stone.

Cause: I over-blended. A stick blender is enormously powerful and the correct technique is to pulse it — short bursts, then stir by hand, then check. I had held the trigger down like a man vacuuming.

Lavender, incidentally, is one of the well-behaved essential oils and does not usually accelerate things much. This was entirely my own work.

Batch four: the brown flecks

Batch four came out of the mould looking genuinely lovely, and I cut it into twelve bars, and I was so pleased with myself that I gave four of them away immediately, which is the behaviour of a fool.

Two weeks later the pretty purple flowers I had stirred through the top had all turned the brown of old tea leaves, and my four bars were out in the world in other people's bathrooms slowly developing what looked like a skin condition.

Nobody tells you this: lavender buds go brown in soap. Always. The alkaline environment destroys the colour. Every impossibly purple lavender soap you have ever seen in a shop is coloured with something else — clay, mica, alkanet, or simply a dye. The flowers are for texture and for the small, honest pleasure of knowing they are yours. If you want purple, you have to add purple.

Before anything else: the lye

Harvesting the lavender

If you are growing your own, the timing matters more than anything you will do later.

Cut when about half the buds on a spike have opened — not when the plant is in full flower, which feels wrong and is. The aromatic oils are at their highest just before full bloom. Cut in the morning, after the dew has dried but before the real heat, which here means somewhere between eight and ten.

Bundle loosely, tie the stems, and hang the bunches upside down somewhere dark, dry and airy for two to three weeks. Darkness is not superstition — sunlight bleaches the colour and degrades the oil. A spare room with the shutters closed is ideal, and has the side effect of making that room smell extraordinary for a month.

On variety: Lavandula angustifolia (true or English lavender) gives the sweeter, softer, more classically “lavender” scent. Lavandin (Lavandula × intermedia) yields far more oil per plant and is what most commercial lavender products actually use, but it carries more camphor and smells sharper — more medicinal, less pillow. Ours is lavandin, because ours was here when we arrived and did not ask.

The recipe that finally worked

This is an olive-oil-led bar in the Mediterranean tradition — gentle, dense, slow-lathering, and improving for months after it is technically ready. The coconut oil is there for cleansing and bubbles, the shea for hardness and feel, and the castor for a creamier lather.

Method

1. Set up. Goggles, gloves, sleeves. Clear the surface. Weigh everything out before you start, into separate containers, so that you are never hunting for something with caustic solution sitting on the counter.
2. Mix the lye. Weigh the distilled water into a stainless or heavy plastic jug. Weigh the sodium hydroxide separately. Add the lye to the water, stirring gently with a stainless or silicone spoon. It will heat violently and go cloudy, then clear. Leave it somewhere safe — a sink is good — to cool to about 40 °C. This takes 30 to 45 minutes.
3. Prepare the oils. Melt the coconut oil and shea butter together over low heat. Take off the heat, add the olive and castor oils — the cold oils will pull the temperature down nicely — and bring the blend to about 40 °C. Getting both within a few degrees of each other is the single easiest way to avoid batch one.
4. Combine. Pour the lye solution into the oils through a sieve, slowly, down the shaft of the stick blender to reduce splashing. The sieve catches any undissolved flakes, which are the source of a great many mysterious problems.
5. Reach trace. Pulse the stick blender in short bursts — two or three seconds — then stir by hand between bursts. You are looking for light trace: the mixture thickens to thin custard and a drizzle from the blender sits visibly on the surface for a second before sinking. With this recipe that usually takes one to three minutes of actual blending. Stop there. If you are unsure whether you have trace, you almost certainly do.
6. Add the lavender. Take the blender out. Stir the essential oil in by hand, then the buds and any clay. Hand-stirring only from this point.
7. Mould. Pour into a silicone loaf mould or a lined wooden one. Tap it on the counter a few times to release air pockets. Texture the top with the back of a spoon if you feel artistic.
8. Insulate. Cover with card and wrap in a towel. This holds the heat in and encourages the batch through gel phase, which gives a more even colour and a slightly translucent bar. Leave it alone for 24 to 48 hours. Do not keep lifting the towel. I know.
9. Unmould and cut. It should be firm enough to hold an edge. Cut into bars. Wear gloves — the soap is still mildly caustic at this stage.
10. Cure. Stand the bars on a rack with air moving around all sides, out of direct sun, turning them once a week. Minimum four to six weeks. With this much olive oil, eight weeks is better and twelve is better still.

Why the cure is not optional

The chemical reaction — saponification — is essentially finished within about 48 hours. Which means that after two days you have soap, technically, and every beginner discovers this fact and reaches for a bar.

Curing is not about safety. It is about water leaving. As the bar dries it becomes harder, milder, and dramatically longer-lasting. An uncured olive soap turns to expensive purple sludge in the dish within a fortnight. The same bar cured for eight weeks will last months and lather better.

So: six weeks of doing nothing, having already done everything. Which is, I am aware, the same lesson the wine cellar keeps trying to teach me, and which I keep needing to be taught.

Things I wish someone had said out loud

• Write the date on the mould. You will not remember. You will stand in front of a rack of identical bars performing archaeology.
• Do not give any away until you have used one yourself for a week. See: batch four, and my four friends with the diseased-looking soap.
• Soda ash is cosmetic. That white powdery bloom on the top is harmless. Steam it, plane it off, or ignore it.
• Keep a notebook. Batch number, oils, temperatures, how long to trace, what the weather was doing. Soap-making in a humid coastal August behaves differently from soap-making in a dry February, and the notebook is the only thing that will ever tell you why.
• Your first good batch will feel like an accident. It is not. It is the first one where you did not rush.

What the lye taught me, since I promised

It is this. There is a category of things that cannot be hurried, and a much larger category of things that can, and almost all the misery in my life has come from mistaking one for the other.

You cannot hurry a cure. You cannot hurry a pruning season, or an olive harvest, or the four years a vine takes before it gives you anything worth putting in a bottle. You cannot even hurry the ten seconds after you swallow a mouthful of wine, which is the only part of the whole business that actually tells you whether you like it.

What you can do — and this is the entire skill, in soap and in wine and in country life generally — is get very good at the part before the waiting, so that when you finally have to stand back and do nothing for six weeks, you are not standing there hoping.

There is a bar from the fifth batch on the shelf in the cellar bathroom. It is a slightly disappointing greyish-lilac and the flowers on top have gone entirely brown. It is the best thing I have ever made.