What's the best way to make soap?

What you’ll need:

Ingredients:
16 ounces coconut oil 

14 ounces palm oil, preferably from a responsible source (alternatives to palm oil can be found here.)

21 ounces olive oil, the cheapest you can find

19 ounces distilled water

Sodium hydroxide (lye)

A 2-pound container of which will make about 4 batches of soap

7 teaspoons essential oil or fragrance oil (optional)

Tools:
A large heat-safe vessel such as an enamelware soup pot*

Measuring cup or small bowl*

Heat-safe vessel, ideally with a handle, such as a heavy glass pitcher*

Silicone spatula or another stirring utensil*

Instant-read thermometer*

Immersion blender*

Scale that can measure in grams and ounces

Soap mold or a 9-inch by 12-inch baking pan*

Plastic wrap (if using a baking pan)

Waxed paper or parchment paper

Teaspoon and additional measuring cup (if using fragrance)

Old towel or blanket

Sharp, thin knife

Rubber gloves

Safety goggles

*Any tools that touch lye should NOT be reused for cooking!

How to make soap at home:

1. Mix the lye. Put on your rubber gloves and safety goggles, and set up in a very well-ventilated area such as next to an open window. If you have access to the outdoors, take this step there. Use your scale and measuring cup to carefully weigh 201 grams of sodium hydroxide and set it aside. Then, weigh 19 ounces of distilled water into your glass pitcher or other sturdy, heat-safe vessel. Now, carefully pour the sodium hydroxide into the pitcher of water, and stir just long enough to make sure it all dissolves. This creates a chemical reaction that heats the water to over 200° F and produces strong fumes at first, so work quickly and be extra careful here—I try to hold my breath while I stir.

The lye now needs to cool to below 100° F. 

2. Prepare the mold and measure out the fragrance. If you're using a wooden loaf mold or a baking pan, carefully line the inside with waxed paper or parchment paper so it's easier to get the soap out later. I often use some masking tape to help hold everything in place. If you use a silicone mold, you can skip this step.

If you like the simplicity of plain rectangular soap bars and think you’ll make more than a couple of batches of soap, having a wooden loaf mold like the one shown here makes the process easy and consistent. 

Now is also a good time to measure out your essential oils into an extra measuring cup, for ease of adding them later. Blending fragrances is probably one of the most fun parts of making soap. For this batch, I used 5 teaspoons of orange essential oil and 2 of sandalwood. Synthetic fragrance oils also work well and are generally less expensive than pure essential oils. Mixing fragrances is akin to mixing spices and other ingredients when experimenting with cooking a dish.

3. Melt and mix the oils. You can now prepare the blend of oils to which you’ll add the lye. If you're using oils that are solid at room temperature, such as the coconut and palm oils in this recipe, you’ll first need to melt them so they can be poured, either by placing the container in a saucepan of simmering water or by melting them in the microwave.

Once your oils are in a liquid state, place your large pot on the scale and weigh (or re-weigh, if you've already done so) each oil into it for precision. Stir everything together and then check the temperature with a heat-safe thermometer. For the next step, the oils need to be between 80 and 100° F.

4. Blend and pour your soap. When both your lye and your oil mixture are between 80 and 100° F, you’re ready to blend. After removing the pot from the heat to a trivet or heat-safe surface, put your gloves and eye protection back on and carefully pour the lye into the pot of oil. They’ll begin to react with each other, turning the mixture cloudy. Begin blending with your immersion blender, and over the next 3 to 5 minutes you’ll see the mixture become thicker and more opaque. You're aiming for a mixture with the consistency of a runny pudding. If you lift the blender out and let some drips fall across the surface of the mixture, you should see them leave a visible pattern, called “trace,” before sinking back in.

Once the soap mixture has reached trace, stir in the fragrance oil, if using, until blended. Carefully pour the finished mixture into your lined soap mold, and cover with the lid (or plastic wrap, if your mold has no lid). Be sure to keep it level, wrap the whole thing in a towel or blanket to insulate it, and leave it undisturbed in an airy out-of-the-way place like a shelf for 24 hours. 

This method that I use for making soap is called the cold process, where no additional heat is used to facilitate or speed up the saponification process. The hot process, on the other hand, uses an external heat source to accelerate it. While cold process soaps take longer to cure (the next stage, below), the choice to use one or the other is entirely personal.

6. Cut and cure your soap. When your clock indicates that 24 hours is done (don't try and rush it), your soap is ready to be removed; many wooden loaf molds have fold-down sides or removable bottoms to make this process easier. If you’ve used a baking pan, you may need to use a knife to help pry the soap loaf out. Cut the loaf into bars with a sharp knife. 

Naturally, you don't want your soaps to crumble when you cut them—and soapmakers have all sorts of ideas on which tools to use to cut soap with. Some use guitar strings, others use butcher's knives. Some DIY-ers even fashion their own instruments. I use a ruler and score the top of the loaf with a sharp knife before cutting to make sure everything stays straight and even. I like generous bars, so I cut them about an inch thick.

The bars need to cure for 4 to 6 weeks (remember what I said about patience?) before being used. This time allows the water in the bars to fully evaporate, resulting in a harder and milder soap. Leave the soap to cure on a paper bag or baking rack in the same airy location. If you use a paper bag, turn the bars once or twice during the curing time to make sure all sides are equally exposed to air.