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A simple guide on how to make cold process soap the easy way. Includes information on each soap making step, temperatures, bringing soap to ‘trace’, molding, and curing soap. This is part four in the Natural Soap Making for Beginners series.
Making cold process soap is the most common way to make soap from scratch. It’s easy enough for anyone to try and you can make soap easily in your own kitchen. Though there’s usually some uncertainty in your first attempt, you’ll get the hang out of it by the second try. I know this because I’ve been running in-person soapmaking workshops since 2014 and they always involve two batches. Once you make cold process soap the first time and succeed, it becomes easier for the next batch, and the batch after that.
In this tutorial, I’ll be showing you the steps I go through when making cold process honey soap. However, you can apply the instructions to practically any cold process soap recipe, including the ones I provided in the piece on easy soap recipes. When you make cold process soap it does refer to temperature but also the process. It’s in contrast with hot process soap which as you can guess is a lot hotter and follows a different set of steps. More on temperature below, but just to reiterate, this is part four of the Natural Soapmaking for Beginners series:
How to Make Cold Process Soap
Cold process soap making involves a lot of ingredients, quite a few instructions, specific 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. Take your time to read through the steps I’ve outlined and then set out everything you need. Even after many years of cold process soap making, I set up my stations every time.
As said previously, this is the last part of the Natural Soapmaking for Beginners series. It’s important to work safely and I encourage you to read the part on equipment and safety. To make cold process soap safely, you should wear rubber gloves, safety goggles, wear long sleeves, and even consider a mask if you’re working in an area with poor ventilation. Many soapmakers have their studios in basements or garages. I also recommend wearing an apron or clothes that you don’t mind ruining with streaks of oil.
Set Up Cold Process Soap Making Stations
My stations include my warming area where I’ll melt the oils and keep most of my utensils. Nearby I have my digital thermometer, spoons, and mini sieve, as well as an immersion blender (also called a stick blender) plugged into the wall. In another area, I keep my bowl of liquid oils and additional measured ingredients, such as pre-measured essential oils in their own ramekin, or a natural soap colorant. I measure all the liquid oils I’m using into the same bowl and the solid oils, such as coconut oil, into a stainless steel pan. I use a digital kitchen scale to measure ingredients precisely.
My cooling area is my sink and this is where I’ll mix the lye and water to make the lye solution. Here I keep my stirring 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 a little cold water. I’ll also measure the distilled water and lye into two separate containers. For safety purposes, I use containers made polypropylene (PP) plastic since they’re heat-proof and lye-safe. Glass can crack because of the heat involved so avoid using it for mixing the lye solution in.
In the last area, I have my soap mold(s) sitting out along with any decorating materials In the last area, I have my soap mold(s) sitting out along with any decorating materials and insulation such as towels. Soap mixture can easily be cleaned off laminate kitchen worktops and it doesn’t ruin them. If you’re working on marble, granite wood, or another material, it’s wise to put down a layer of freezer paper (or baking paper/greaseproof paper).
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.
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 though: ensure that your goggles and gloves are on, that kids and pets are not going to disturb you, and that the area you’re planning to work in is well ventilated. Outdoors is best but if you need to work inside, set up your lye solution area near an open window. Also, ensure that your distilled water is room temperature or cooler. Warm liquids can cause the lye solution to volcano.
To make the lye solution, slowly pour the lye (it comes in grains or granules) into the water and stir with a stainless steel or silicone implement. Always pour the lye into the water, not the other way around. The chemical reaction between lye and water produces heat and steam so please be careful and don’t breathe in the steam. Make sure to stir the ingredients together thoroughly but gently and when you’re finished place the lye solution someplace to cool.
If it’s cold, I have set the lye solution outside to cool before. I don’t do that very often though now because I have outdoor cats and I don’t want them to get hurt. There are also wild birds that might land in it, or some other awful accident waiting to happen. Instead, I set the jug of lye solution in cold water in my kitchen sink. It helps to cool the lye solution down quicker and is much safer.
Melt the Solid Oils in the Soap Recipe
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. 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 since it’s quite heavy and likes to stick to the bottom. Get every last drop of oil you can since soap recipes are measured very precisely. I use a silicone spatula to ensure I scrape that bowl or jug clean.
Also, if you’re making a single-color soap recipe add any liquid oil (or water) that you’ve tinted with a colorant at this point. Pour it through the sieve and into the pan of oils to catch any pieces that haven’t been mixed in. Not all soap recipes call for a colorant but many will and adding it before mixing helps distribute the color more evenly.
Cold Process Soap Making Temperatures
When I was first starting to make soap, one of the most confusing parts for me was at what temperature do you mix the lye solution and the oils? Do they have to be at the same temperature? Why?
Soap making temperatures can be different based on the ingredients you use and personal preference. Temperature affects not only how quickly your soap will saponify, but also its color and texture. There are several factors that you’ll need to consider when choosing a soaping temperature and they’ll include batch size, type of mold if sugars (honey, milk, sugar) are used, melting temperature of butters and oils being used, and what color you hope your batch will turn out.
That’s why taking the lye solution and the oil’s temperatures is important when you make cold process soap. Though old skool soapmakers sometimes use analog glass thermometers, the quickest, cleanest, and safest way is with an infrared thermometer. I also used to use digital kitchen thermometers and they work well too.
Ideal Temperatures for Cold Process Soap Making
Personally, I make soap when the oils are between 85-120°F (29-49°C) and err on the cooler side if I’m using sugars. I only make cold process soap at higher temperatures when I’m using beeswax as an ingredient. Also, the lye solution should be at, or within ten degrees of the oil’s temperature. If there’s a big difference in the oil and lye solution temperature, then strange things can happen including false trace.
As a beginner, I’d recommend that you stick with the temperatures recommended by other soapmakers. In my soap recipes, I always give the temperature I recommend for that particular mix of ingredients.
Sometimes getting the lye solution to cool down to the same range as the oils can be challenging. When you make cold process soap, please don’t let this step stress you out. Try to get them as close as possible but if the lye is getting too cool just get them mixed. That’s because it’s difficult to warm the lye solution up safely.
Oils are easier to control though. To cool them, you can float the pan in the sink of water or even set them in the fridge. If the oils get too cold, you can gently warm them on the stove.
Some soap makers work with lye solutions that are room temperature while their oils are warm. As long as the overall temperature once you mix the lye solution and the oils are above the lowest melting point of your oils then you’re fine.
Bringing your Soap Ingredients to Trace
Now comes the exciting part. To make cold process soap from your ingredients 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 too. Give it a little tap against the bottom to release any air that might have been captured underneath. While the immersion blender is turned off, stir the ingredients gently. Then bring the immersion blender to the center of the pan and turn it on for a few small pulses. For small batches, I recommend not moving the immersion blender around while you’re pulsing since it can cause the soap batter to splatter.
Repeat the stirring (with immersion blender off) and pulsing until the soap comes to a thin trace. Depending on your batch size it could take anywhere from 1-10 minutes. Trace is when the oils and lye solution are first emulsified then begin to saponify. During saponification, the soap will thicken and harden up and trace is the first stage of this. You’ll know when your mixture has traced when it reaches a pudding-like consistency. Once you lift your immersion blender out of the mix, you’ll notice that you’ll be able to see a little dribble of soap on the surface of the soap batter.
Trace will continue thickening from a light batter consistency to thick and gloopy. Work quickly or sometimes it will firm up inside your pan. It’s a little difficult at first to understand what trace is, but you’ll see it happen in my soap making videos.
Adding Ingredients at Trace
Once the soap has come to trace you’ll need to work quickly to add in the last ingredients. These may include a specific superfatting oil, essential oils, colorant (some are added at this point too), exfoliant, and other extras. You add these after trace because the steps before could destroy fragile ingredients. Heat can evaporate essential oils, for example.
Also, if you add whole ingredients before the soap has traced, then the immersion blender will pulse them up. You could want this and do it deliberately, but you might not be aiming for that and so we add exfoliants and extras once the immersion blender is set aside. The last reason specifically touches on the super-fatting of your recipe.
Superfatting Cold Process Soap
Most modern soap recipes include a superfat, meaning an extra amount of oil that makes the soap gentle and conditioning. The way it works is that lye in a recipe can only convert a certain amount of oil into soap. If you add more than what it can interact with, that extra oil stays free-floating in the soap.
Most of my recipes do not include a superfat step. I have the superfat built into the main recipe so that your free-floating oils are a combination of all the oils you use. I find this way of super-fatting easier for beginners since it doesn’t require an additional step. However, sometimes you’ll come across a recipe that will call for it. If it’s a solid oil/butter, like cocoa butter, you’ll need to melt it in advance and add it after the soap traces. You do not need to worry as much about the temperature of the superfat oil but try to keep it on the lower side if you can.
Adding Antioxidants to Cold Process Soap
Some soap makers use antioxidants in soapmaking and others think they’re unnecessary. The role of antioxidants is to help keep free-floating oils in your bars from going rancid over time. However, if all of your ingredients are well within their best-by date, and you’re not using ingredients that go rancid quickly (hemp seed oil, for one), then you probably don’t need to worry about it. There are two main antioxidants that soap makers use: Grapefruit seed extract (GSE) and Rosemary Oleoresin Extract (ROE). ROE has been shown through tests to be more effective.
Read up on them and choose which one will be best for you. I should also say that antioxidants are not true preservatives but work to keep the extra oils in your soap from going rancid. They help stall the oxidization of free-floating oils. Soap does not require preservatives so you do not need to add any. The pH and very low amount of water left in soap bars rule out bacteria wanting, or being able, to colonize it.
Pouring Soap into Molds
Once you’ve added your last ingredients, and stirred them in well, the soap is ready to be poured into the mold(s) — I have a guide to soap molds that you can read here. Most simple soap recipes are a single color and all you need to do is pour the soap batter into the mold. Scrape as much out of the pan as possible and into the mold. I also find that it helps to lift and plunk your molds down a couple of times after the soap has been poured in. This helps settle the mix into all the corners and release trapped air bubbles. Once you’re finished with the next steps you can also come back to your dirty dishes and safely clean up after soapmaking.
Insulating the Soap
Now you’ll have a choice on whether you’d like to insulate your soap or not. Insulating it will keep the temperature warm and steady over the next day or so. Keeping it warm will cause the soap to gel and this will deepen the color and add slight transparency to the finished bars.
You can insulate your soap in a closed wooden box, or line the top of the soap with cling film and wrap a big fluffy towel around the mold. In summer, or in warm regions, soap will gel without any insulation whatsoever. You can simply leave the molds on the countertop. In winter or cold climates, a towel might not be enough for small batches. When it’s cold I preheat the oven to 170°F (76°C) and place the soap inside after I pour it into the mold. I’ll turn the oven off after the soap is inside if there are any ingredients that might make the soap heat up. Otherwise, I’ll leave the oven on for 15-60 minutes before turning it off and letting the soap cool. This is called oven-processing soap.
If you choose not to insulate your soap then the color will be much lighter and opaque. Sometimes the center will be warm enough to gel but the outer edges are too cold. In that case, you’ll get a partial gel and your bars will have a darker circle in the middle. It’s purely aesthetic, so don’t worry if it happens to you. If you want to avoid your soap gelling at all you can put it in the fridge after you’ve poured it in the mold. Keep it on the bottom shelf and away from open food and it’s perfectly safe.
Unmolding and Cutting Soap Bars
Once you’ve made cold process soap and poured it into the mold you’ll need to wait. I tend to recommend leaving it in the mold for 48 hours since by that time the ingredients will have nearly completed saponifying. That means very little lye is still present in the soap and it’s safer to handle.
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 bars with an ordinary stainless steel kitchen knife. You can also use a pastry cutter, or wire cutter, to cut your soap block into bars.
It’s up to you how large or small you want to cut your bars. However, if you want exact-sized bars then measure loaves with a ruler or invest in a professional soap cutter. Some are relatively inexpensive and good for the small producer. A hack that I used to use for exact-sized soap bars was a miter box that I’d marked out with a sharpie and a kitchen knife.
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 you take when you make 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 for making gentle soap since soap needs at least a month to form the crystalline structure that is so important to good handmade soap. You cannot rush this step and you can learn more about it over 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 just 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, gift it, or even sell it if you comply with your region’s laws and business practices.
Hopefully, this tutorial on how to make cold process soap has been helpful. If you have any questions please feel free to leave them in the comments section. There’s also a lot of information in the other three posts of this series so have a browse through them too. For more soapmaking inspiration you can browse recipes and ideas here.