Making soap from scratch is one of those things that sounds like it belongs in a pioneer museum, right up until you do it once and find yourself pricing out molds at midnight. It's part kitchen chemistry, part cooking, and part patience, and the first time you cut a loaf you made yourself is a genuinely good feeling.
This guide walks through cold process soap, the way most handmade soap (ours included) is made. It's written for someone who has never touched lye. Read it all the way through once before you buy anything.
The three ways to make soap
Melt and pour uses a premade soap base that you melt, scent, color and pour into molds. No lye handling, and it's ready as soon as it sets. It's a lovely way to start with kids, though technically someone else already made the soap.
Cold process means mixing oils with a lye solution yourself and letting the reaction happen in the mold. You control every ingredient, and the bars cure for several weeks before they're ready. This is what the rest of the guide covers.
Hot process starts the same way, then cooks the batter (usually in a slow cooker) to finish the reaction faster. The bars look more rustic and can be used sooner, though they still improve with a little drying time.
How soap actually happens
Soap is what you get when fats or oils react with a strong alkali, in this case sodium hydroxide, better known as lye. The reaction is called saponification, and it turns oil and lye into soap and glycerin. Done right, none of the lye is left in the finished bar. It's all been used up making soap.
That last part is why measuring matters so much. Every oil needs a specific amount of lye to turn into soap, and soapmakers deliberately use a little less lye than the oils could take, so a small share of oil stays unreacted. That cushion is called the superfat, and around 5% is a common starting point. Our guide to lye soap goes deeper on all of this.
Safety first, and we mean it
Lye is caustic. It can burn skin and seriously damage eyes, and when you mix it with water the solution gets hot fast and gives off fumes for a minute or two. None of that should scare you off, but all of it should be taken seriously.
- Wear safety goggles (not glasses), gloves and long sleeves the whole time lye or raw soap batter is out.
- Always add lye to water, never water to lye. Pouring water onto lye can make it erupt.
- Mix your lye solution somewhere well ventilated, like next to an open window or under a range hood, and don't lean over it.
- Use stainless steel, heat-safe glass or sturdy polypropylene plastic (look for a 5 on the bottom). Never use aluminum, which reacts with lye.
- Keep your soap tools for soap only, and keep kids and pets out of the room.
- If lye or batter gets on your skin, rinse it with plenty of running water. If anything gets in your eyes, rinse for a long time and get medical help.
A label on the lye container is worth reading too. It'll tell you more than we can here.
What you'll need
- A digital kitchen scale that measures in grams. Soapmaking is done by weight, never by cups.
- Sodium hydroxide (100% lye, sold for soapmaking or in hardware stores).
- Distilled water.
- Your oils (more on choosing them below).
- A stick blender. You can stir by hand, but you'll be stirring for a very long time.
- Two containers, one for the lye solution and one for the oils, plus a silicone spatula.
- A thermometer, ideally an infrared one.
- A mold. A silicone loaf mold is easiest, but a lined shoebox has started plenty of careers.
- Fragrance or essential oil if you want scent, and that's optional.
Choosing your oils
Different oils make different bars. Coconut oil gives big, bubbly lather and a hard bar, but too much can feel stripping. Olive oil makes a gentle, creamy, slow-to-harden bar (an all-olive bar is a castile soap). Butters like shea and cocoa add hardness and a silky feel. A little castor oil helps the lather hang around.
A friendly first recipe, by weight, looks something like this.
- 45% olive oil
- 30% coconut oil
- 20% shea butter
- 5% castor oil
For a 1,000 gram batch of oils, that's 450 g olive, 300 g coconut, 200 g shea and 50 g castor, which fills a standard loaf mold. Now here's the important part. Don't take a lye amount from any recipe on faith, including one you found online. Plug your exact oils and weights into a lye calculator at about a 5% superfat and use the numbers it gives you. Our recipe scaler will resize a recipe to fit your mold, and the cost calculator tells you what each bar costs to make.
Making the soap, step by step
- Get everything ready. Gear on, mold lined or set out, oils and lye weighed out separately, scent measured. Once the batter starts, things move.
- Make the lye solution. Pour the measured distilled water into your heat-safe container, then slowly add the lye to the water and stir gently until it dissolves. It will get very hot and cloudy, then clear. Set it somewhere safe to cool.
- Melt the oils. Gently melt the coconut oil and shea butter, then add the liquid oils. Adding the room-temperature oils helps bring the temperature down.
- Bring both to temperature. Most beginners aim for both the lye solution and the oils to be somewhere around 100 to 120°F, within about ten degrees of each other. It doesn't have to be exact.
- Combine. Carefully pour the lye solution into the oils (pour along the spatula to avoid splashing).
- Blend to trace. Pulse the stick blender in short bursts and stir between pulses. Within a few minutes the mixture thickens to "trace," when a drizzle on the surface leaves a faint trail before sinking back in. Think thin pudding.
- Add scent. Stir in your fragrance or essential oil at light trace. Our fragrance calculator will tell you how much to use for your batch size, and it's worth using, because more is not better.
- Pour and insulate. Pour into the mold, tap it on the counter to knock out air bubbles, and cover it loosely with a towel or cardboard for a day or so.
- Unmold and cut. After 24 to 48 hours, when the soap is firm, pop it out and cut it into bars. Keep wearing gloves, since fresh soap can still be caustic for the first few days.
- Cure. Stand the bars on a rack or shelf with air around them, somewhere cool and dry, for four to six weeks. Turn them now and then. This is when the extra water evaporates and the bar hardens into something that lasts.
Why the wait?
Fresh cold process soap is soft and still finishing up. Over the cure it loses water, gets harder and milder, and lasts much longer in the shower. It's the hardest part of soapmaking for most people, and also the part that makes the biggest difference. Our post on how long a bar of soap lasts gets into why cure time matters.
When things go sideways
- It seized. The batter turned solid in the pot, usually from a fussy fragrance oil or temperatures that were too high. Glop it into the mold quickly anyway. It'll be ugly and perfectly usable, or you can rebatch it.
- White powder on top. That's soda ash, a harmless reaction with air. Plane it off or steam it away, or just leave it.
- Oil pooling or a greasy bar. Usually a measuring problem or not blending to true trace. Don't use it. Recheck your numbers in the calculator.
- Orange spots weeks later. Those are oils going rancid, often from too many soft oils or old oils. Use those bars up first.
- Soap that's too soft to cut. Give it another day or two in the mold. Recipes heavy in olive oil take their time.
Where to go from here
Once the basics feel easy, the fun part starts. Swirls, layers, milks, botanicals and fragrance blends. Our soap making recipes are a good next step, and if you want something richer, try goat milk soap. For the bigger picture of what you're doing, there's our guide to cold process soap making.
And if, somewhere around step 2, you decide you'd rather buy soap than make it, no judgment here. Our whole shelf was made exactly this way, a few weeks before it got to you.