A step-by-step guide on how to make cold process soap. Includes information on each soapmaking step, temperatures, mixing lye solution, bringing soap to ‘trace,’ molding, and curing soap. This is part four of the Natural Soap Making for Beginners series.
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Thus far, in this series, we’ve looked at natural soap ingredients, equipment and safety, and easy soap recipes. Now we’re going to go through exactly how to make cold process soap from scratch. I’ve been teaching beginners how to make soap through in-person workshops and the new online course for over a decade. Through them, I have learned some of the easiest ways to ensure first-time success with making handmade soap. The instructions and tips below will help you easily create small 1-lb (454 g) batches of soap in your kitchen. This is the standard-size recipe I share here on Lovely Greens, creating about six bars in each. It’s the perfect-sized batch for beginners to make.
Making cold-process soap is the most common way to make soap and involves mixing oils, fats, lye solution, and soap additives in a precise way, usually with the help of an immersion blender. You then pour the soap batter into molds, allow it to harden, then cure the homemade soaps for at least a month before using them. I explain in much more detail below, and by the end of this piece, you’ll understand the general steps you take to make most cold process soap recipes. You’ll also have answers to many of the most common questions that come up for beginner soapmakers.
The Natural Soapmaking for Beginners Series
How to Make Cold Process Soap
There are several ways to make soap, but the process I’m about to take you through is cold process soapmaking. It’s called cold process not because all of the ingredients are cold but to differentiate it from hot process soap, which is cooked, typically in a crockpot. Cold process soap is usually made at room temperature to about 120°F (49°C), depending on the oils used and the batch size. Once poured into the mold(s), the soap then needs two days to finish the vast majority of saponification and four weeks to cure and be ready for use. Here are the basic steps to how to make cold process soap:
- Measure out the ingredients.
- Make the lye solution.
- Gently melt the solid oils (if any).
- Add the liquid oils to the melted solid oils.
- Pour the lye solution into the oils.
- Bring the ingredients to trace.
- Pour soap into the mold(s).
- Cut and cure the soap.
Getting Ready to Make Soap
The above basic steps pertain to making a simple soap without soap additives. If you’re going to naturally color soap or add scent or other ingredients, there may be additional steps. I’ll go through that a little later, but first, let’s get ready to make soap. The first thing that we need to do is get organized.
Cold process soap making involves various ingredients, instructions, pieces of equipment, and safety precautions. That’s why it helps to prepare everything you need in advance. This includes measuring out ingredients and having your station set up. If there’s a moment of panic anywhere along the way, then it definitely helps. Hurriedly measuring out ingredients or searching for an important piece of equipment can lead to mistakes. Before you make soap, you’ll want to:
- Set up your soapmaking station with your required soapmaking equipment.
- Prepare yourself by wearing an apron, goggles, and rubber gloves. Wear sensible clothes that you don’t mind getting ruined by splatters of oil.
- Measure the solid oils into a stainless steel pan.
- Measure the liquid oils into a bowl or jug.
- The water amount gets measured into a heat-proof polypropylene jug.
- Measure the lye into its own container.
- Soap additives should also be measured and had at the ready.
Your Cold Process Soapmaking Station
When you’re making cold process soap, it helps to have equipment and ingredients laid out at different stations. Mine includes four different stations with their particular ingredients and equipment set out and ready to go before I start making soap. The first is a warming area, where I’ll melt the solid oils and keep most of my utensils. It’s going to be where your heat source is, whether that’s a kitchen stove or a portable hob. Nearby I have my digital thermometer, spoons, a small sieve, and an immersion blender (also called a stick blender) plugged into the wall.
In another place close to my warming area, I keep the bowl of liquid oils and additional soap additives, such as essential oils. I measure all the main liquid oils (not essential oils) into the same bowl using a digital kitchen scale to measure them precisely. Soap additives for small batches are often easier to measure in teaspoons, so I’ll either pre-measure them into ramekins or directly measure them into the soap batter.
Cooling and Molding Areas
The third station is a cooling and lye-mixing area. This is usually at my sink, where I’ll mix the lye and water to make the lye solution. Here I keep a stirring implement, either a silicone spatula or a stainless steel spoon, at the ready and make sure to pop open the window for ventilation. In preparation for cooling my lye solution, I fill the sink with an inch or so of cold water.
In the last area, I have my soap mold(s), any decorating materials, and insulation, such as towels or old blankets. Soap batter can easily be cleaned off laminate kitchen worktops, and it doesn’t ruin them. However, if you’re working on marble, granite wood, or another material, putting down a layer of grease-proof paper or cardboard (or both) to protect your worktops is wise.
Making Lye Solution for Cold Process Soap
Though some people find it a bit scary, working with Sodium hydroxide (lye) is a necessary part of soap making from scratch. All handmade soap is made using lye, and I go through why in How to Make Soap Without Lye.
The very first step you take to make cold process soap is to mix lye and water together to make a lye solution. Safety first; ensure that your goggles and gloves are on, that kids, other people, and pets will not disturb you, and that the area you plan to work in is well-ventilated. Outdoors works, but it’s not always ideal or hygienic. If working inside, I recommend setting up the lye solution area near an open window. You should also ensure that the distilled water (or other liquid used for the lye solution) is at your room’s ambient temperature or cooler. Warm liquids can cause the lye solution to furiously bubble up and out of the jug.
To make the lye solution, carefully pour the lye (it comes in grains or granules) into the water and stir immediately. Always pour the lye into the water, not the other way around. The chemical reaction between lye and water produces heat and fumes, so please be careful and don’t breathe it in. Make sure to stir the ingredients together thoroughly but gently, and when you’re finished, place the lye solution in the sink to cool.
Melt the Solid Oils on a Heat Source
You generally make cold process soap with both liquid oils and solid oils. That means that the next step after mixing the lye solution is to melt the solid oils. Coconut oil is a popular solid oil for soapmaking, as is tallow, cocoa butter, and shea butter. Place the pan filled with your pre-measured solid oils on the stove and turn it on to the lowest heat possible. Keep a close eye on it, stirring and breaking up any larger chunks to speed things up. Make sure to take it off the heat as soon as it’s completely melted. You could even take it off shortly before since the residual heat will melt any small pieces of oil.
Add the Liquid Oils to the Melted Oils
Once the solid oils are melted, pour the liquid oils into the pan too. Not the essential oils though, just the liquid oils such as olive oil, sunflower, and castor oil. If you have castor oil in the recipe, give the entire bowl a stir before pouring. Stirring the oils together helps dilute the stickiness of castor oil, and it pours from the bowl more easily. Also, get every last drop of oil you can since soap recipes are measured very precisely. I use a silicone spatula to scrape the bowl or jug clean.
If you’re making a single-color soap recipe, add the colorant at this point if it’s not already in the oils or lye solution. If it’s mixed into oil or water, pour it through a small sieve and into the pan of oils to catch any pieces that haven’t been fully incorporated. Not all soap recipes call for a colorant, but many will, and adding it before mixing the oils with the lye solution helps distribute the color more evenly.
Cold Process Soap Making Temperatures
Next, I recommend cooling both the lye solution and the pot of oils to around 100°F (38°C). You’ll sometimes hear other soapmakers scoff at temperature but pay that no heed, at least initially. If you are diligent with keeping the ingredients around this general temperature, you can be more confident that your soap won’t volcano, crack, or have unwanted surprises inside when you cut it into bars. You can also avoid other big soapmaking fails like false trace.
As you become more experienced, I encourage you to learn about room-temperature soapmaking and experiment with raising the temperature to help initiate gel phase or to incorporate beeswax in soap recipes. For now, though, stick to 100°F (38°C) for small, simple soap recipes, and you’ll be sure of success. Though old-school soapmakers sometimes use analog glass thermometers, the quickest, cleanest, and safest way is with an infrared thermometer. Digital kitchen thermometers also work well.
Bringing the Soap Ingredients to Trace
Once the lye solution and oils are around 100°F (38°C) and about ten degrees of one another, it’s time to combine them to make soap. You’ll first pour the lye solution through a sieve and into the pan of oil. The sieve is to make sure that no bits of undissolved lye make their way into your soap. Once the lye solution is in the pan, submerge the head of the immersion blender in the mixture. Give it a little tap against the bottom to release any air that might have been captured underneath.
With the immersion blender turned off, use it as a spoon and stir the ingredients gently. Then bring the immersion blender to the center of the pan, hold it firmly against the bottom of the pan, and turn it on for a few small pulses. It’s like magic seeing those first stages of emulsion! Don’t get overly excited, though; focus on your immersion blending technique. Pulse, then stir, and repeat.
With small soap batches, I recommend not moving the immersion blender around at all while you’re pulsing since it can cause the soap batter to splatter or introduce air bubbles into your soap. If you’re unsure about this step, I show exactly what to look for in the recipes in the soapmaking course.
Look for a Warm Custard Consistency
Keep pulsing and stirring until the soap comes to a thin trace. Depending on your batch size, it could take anywhere from two to ten minutes. Trace is when the oils and lye solution are emulsified and begin saponifying. Sometimes in soap recipes, you’ll be instructed to look for something called emulsion. However, this is a more challenging stage to look for as a beginner. Instead, look for a thickening of the soap batter – a light trace is very fine, like warm, custard. Pulling the immersion blender out will leave the faintest dribbles on the surface of the soap batter.
Medium trace is easier to look for and can be fine for simple soap recipes. At this stage, it’s thicker, like pudding. If you mix to this stage, you’ll need to work quickly since the batter will continue to thicken up and set solid in the pan. Trace is something that I show how to look for in my online natural soapmaking course.
Adding Ingredients at Trace
Once the soap has come to trace, you’ll need to work quickly to stir in the last ingredients. These may include essential oils, natural soap colorants, exfoliants, antioxidants, and other extras. It’s common practice to add these ingredients at trace, but many can be added before this stage, too. Especially if you’re making single-color, single-fragrance batches of soap. In many cases, it’s really down to personal preference and the recipe itself.
Also, if you add botanical ingredients before the soap has traced, then the immersion blender will pulse them up into fine pieces for you. That’s the case when making this calendula flower soap recipe. You might not want that, though, such as in the case of adding poppy seeds. If there’s ever a question on when to add a soap additive after trace is probably your best bet.
Pouring Soap into Molds
Once you’ve added your last ingredients and stirred them in well, it’s time to pour the soap batter into the mold. There are quite a few different types of soap molds that you can use for small soap batches. My favorites include this 6-cavity soap mold, a small loaf mold, and repurposing drinks cartons into free soap molds. I use the latter in my in-person soapmaking workshops.
Tip the soap batter out of the pan and into the mold(s) while it’s still relatively liquid. Scrape as much out of the pan as possible with a silicone spatula and into the mold. If the soap batter is thick and holding form after pouring it in, you can lift the mold up and gently plonk it on the counter. This helps settle the mix into all the corners and release trapped air bubbles. When you’re happy with how the soap batter looks in the mold, you can decorate the surface with any extra texture and ingredients. Once you’re finished with the next few steps, you can also come back to your dirty dishes and safely clean up after soapmaking.
Gelled and Ungelled Soap
After you’ve poured the soap into the mold(s), you can leave the mold in a safe place on the counter for the next two days. For cavity molds, this works well, and if your home isn’t hot inside, the soap will likely not gel. Gelling is a heating-up phase that happens after the soap is poured into molds. If the soap fully gels, the color and appearance of the soap can change. It can become deeper, more vibrant, and have an almost translucent quality to the outer layer of soap. It’s purely aesthetic, and some soapmakers ensure all their soap is gelled.
Soap that has not gelled is more opaque and pastel in color. The typical white bar of soap that most people can picture in their minds is un-gelled soap. Many people love the look of un-gelled soap, and some soap makers ensure all their soap is un-gelled.
There is something called partial gel that most soapmakers would prefer to avoid, though. This typically happens in loaf molds, where the inside of the soap gets hot and gels while the outer edges remain cool. The outer edges turn out a softer, less vibrant color. You usually only realize that it’s happened when you start cutting it into bars! It’s not considered a professional look, but if it happens to your personal batches, don’t worry about it. Partial gelling doesn’t affect the soap’s qualities, only its aesthetics.
To avoid partial gelling in loaves of soap, you can either put the soap in the refrigerator to stop it from gelling at all or take steps to force the soap into fully gelling. Those steps can include oven processing or, more commonly, insulating the soap with various materials. Insulating soap will keep the temperature warm and steady over the next 12-24 hours, causing the soap to gel and have an even and vibrant color throughout.
Insulating involves covering the wet soap’s surface with cling film or a cutout piece of cardboard and then wrapping the entire soap mold in a big fluffy towel or old blanket. Alternatively, you can put the soap mold into a wooden box. Some silicone molds are even sold with an outer wooden casing and lid to help you gel your batches.
Another thing to know is that in summer or in warm regions, soap can fully gel on your worktop without any insulation whatsoever. That’s not been my experience, though, so I take measures to fully gel or stop the soap from gelling altogether. I recommend that you do the same.
Unmolding and Cutting Soap Bars
Unless otherwise stated, it’s best to wait two days from the point that you made the soap to remove it from the mold(s) and cut it, if necessary. This gives time for the majority of the saponification to complete and for the soap to harden up. There’s nothing worse than trying to remove soft and sticky soap from a mold.
If you’ve used cavity-style silicone molds, you can pop the bars out and set them on shelves to cure right away. With loaf molds, take the block of soap out and cut it into soap bars with a stainless steel kitchen knife or a length of wire.
How large or small you want to cut your bars is up to you. However, measure loaves with a ruler or invest in a professional soap cutter if you want exact-sized bars. Some are relatively inexpensive and good for the small producer. A hack I used for exact-sized soap bars was a miter box that I’d marked out with a sharpie and a kitchen knife to cut.
Curing Cold Process Soap
Your soap looks finished and might even smell pretty nice at this point, but it’s not ready yet. The last step when making cold process soap is to cure it. The curing process gives time for the soap to finish saponification. It’s also to give it time to dry and for the water to evaporate out of your bars. Lastly, it’s important to make gentle soap since soap needs at least a month to form the crystalline structure, which is important for creating gentle handmade soap with excellent lather. You cannot rush this step and can learn more about it here.
Cure handmade soap by placing it on a layer of wax/greaseproof paper in a dry, airy, and room temperature place out of direct sunlight. Space the bars out to increase airflow and leave them there for at least four weeks. It sounds like a long time but try to forget about the soap and move on to other projects for a while. Before you know it, the time will have passed, and they’ll be ready to use.
After the cure time is up, you can use the soap, decorate it in natural soap packaging, and even sell it if you comply with your region’s laws and business practices. Until you use it, store your bars in the open so that they can breathe. The worst thing you could do is put them in a sealed container or wrapping, which often makes the bars sweat and the superfat go rancid and smell odd.
Natural Soap Making for Beginners Course
This piece concludes the free soapmaking series, but if you’d like more one-on-one guidance, I’d like to invite you to enroll in my Natural Soapmaking for Beginners Online Course. It includes sixteen instructional videos, including soap recipes that lead you through using different ingredients, including essential oil, clay, dried flower petals, and goat milk. You also get printables and are shown exactly how to prepare, measure, and make handmade soap at home. It’s a comprehensive course that will get you started making soap pronto! Learn more