Transform raw ingredients into handmade soap
A simple guide on how to make cold-process soap. 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.
The cold-process method 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. Soap making involves a lot of ingredients and steps so just try to keep organized.
In this tutorial, I’ll be showing you the steps I go through when making a honey soap. However, you can apply the instructions to practically any soap recipe, including the ones I provided in the last post. The video below shows how to make cold-process soap with this Lemongrass soap recipe. Cold-process does refer to temperature and is 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.
Assemble your Ingredients and Equipment
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.
Soap Making Stations
My stations include my warming area where I’ll melt the oils. Nearby I have my digital thermometer, spoons, and a mini strainer and an immersion blender plugged into the wall. In another area, I keep my bowl of liquid oils and additional measured ingredients. I measure all the liquid oils I’m using into the same bowl unless I’m setting aside one specifically as the ‘superfatting’ oil.
My cooling area is my sink and this is where I’ll mix the lye and water solutions. 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 couple of inches of cold water.
In another area, I have my soap molds sitting out along with insulation materials such as towels and the wooden box I molds in. Lastly, I use a kitchen scale to measure the solid oils into a stainless steel pan.
Melt the Solid Oils
Are you ready to start making soap? The first step is to begin melting the solid oils. Put the pan on the stove and turn it on to the lowest heat possible. Keep a close eye on it while you move to the next step. Stir the oils and break 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.
Making the Lye Solution
Once your solid oils are on the hob turn your attention to your water (or other liquid) and lye. First, make sure that your goggles and gloves are on and that the area you’re planning to work in is well ventilated – open a window if necessary.
Please also ensure that any children and pets are out of the room so that you won’t be disturbed and that the likelihood of an accident is minimized. Now you’ll need to think of cooling methods. Once your lye and water have been combined the mixture will get very hot and will need to be cooled either in a basin of water or outdoors. Please don’t put it in the fridge since the solution gives off unhealthy fumes that you don’t want to come into contact with food.
Though some people find it a bit scary, working with Sodium hydroxide (lye) is a necessary part of soap making from scratch. All soap is made using lye.
Mixing the Water and Lye
Measure your distilled water and lye into two separate containers and for safety purposes, use containers made of glass, pyrex, or Polypropylene (PP) plastic. Take both containers to a ventilated area near your cooling station. Now slowly pour the lye into the water and stir with a stainless steel utensil. The chemical reaction between lye and water produces heat and steam so please be careful.
Using caution when mixing lye
A word of caution. Pouring the water into the lye can be dangerous. Always pour the lye into the water to avoid the solution volcanoing up out of the container.
Also of importance is to make sure that your water/liquid is at least at room temperature when you add the lye. This is especially important for those of you who are planning on making soap using a herbal infusion. The volcano in that situation can be even more dramatic.
If your water is even lukewarm your lye solution can start to boil violently and even volcano out of your container. This volcano action can also happen if you have any ‘sugars’ such as honey or milk in your liquid.
One of the most confusing parts about making soap 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 will 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.
Ideal soaping temperatures
Personally, I make soap when the oils are between 85-130°F (29-54°C) and err on the cooler side if I’m using sugars. Also, the lye solution should be at, or within a few 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.
Cooler temperatures are great for when you’re working with honey, milk, juice, and other sugars. These ingredients have a tendency to quicken trace and heat soap up even after molding. The heat can discolor your soap, crack it, and cause partial gels. Cooler temperatures slow down trace and reduce many issues, including glycerin rivers. It does, however, increase the chance of your soap forming soda ash.
The warmer the temperature, the more intense the color your soap will be, and the quicker your soap will trace. I soap at warmer temperatures when I’m using ingredients like madder root and alkanet since they look so much more vibrant when gelled. However, if you mix cold-process soap over 130°F (54°C) then you risk having issues including volcanoes, cracking, and discoloration. There are a few exceptions, such as in making beeswax soap, but the rule is to keep temperatures within a window
For larger batches that are going into large molds, many soap makers tend to work with lower temperatures around or below 100°F. This is because of the tendency for large batches of soap in loaf molds to stay hotter in the center than on the outsides. This means that there’s a chance of a deeper color in the middle and lighter on the outside.
Most soap makers that create large batches are doing so to sell them on to the public and a strangely colored bar of soap is less marketable than one with homogeneous color and texture.
If you’re making a small batch of soap and want a medium intensity color then I’d recommend choosing a temperature closer to 110-120°F. If you’re making a small batch and would like a soft and opaque color then stick with lower temperatures of around 90-100°F.
Having honey, milk (check out my goat milk soap recipe), or sugar in your recipe will cause your soap batter to heat up. It will continue to heat up even after it’s been poured into molds. That’s why soap with ‘sugars’ in it can crack on the top if you’re not careful about temperatures.
If you plan on using these ingredients then consider using lower temperatures. Temperatures above 110°F (43°C) can caramelize or burn the sugars resulting in a different smell and color than you were expecting. You can also use this to your advantage. The honey soap I’m making in the photos is honey-brown due to caramelization rather than the raw honey on its own.
A higher mixing temperature will mean that the color of your soap will deepen dramatically due to a reaction called ‘Gelling’. If you’re after soft and light-colored bars then use lower temperatures. Please also read the section below on insulation since this will affect the color of your soap too.
Once your hard oils are fully melted, add your liquid oils and any additional colored oils and stir well. Check the temperatures of both the lye water and pot of oils. Adjust them until they’re within ten degrees of each other and close to your target mixing temperature.
If the oils are too hot still, you can float the pan in the sink of water and stir it to cool. If they’re too cool, pop them on the heat again — they heat up quickly so keep an eye on them in that case.
Lye that gets too cool can’t be warmed again. 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 to Trace
Now comes the exciting part. Pour your lye-solution through a strainer and into your oils as shown above. The strainer is to make sure that no bits of undissolved lye make their way into your soap. Now submerge your immersion blender into the pan, giving it a little tap to release any air that might have been captured underneath. Start with a few short pulses and then stir.
Repeat this until you come to ‘Trace’ – depending on your batch size it could take anywhere from 1-10 minutes. Trace is when the oils and lye-solution combine into soap through a process called saponification. You’ll know when your mixture has traced when it reaches a thin pudding-like consistency. Once you lift your immersion blender out of the mix, you’ll also notice that you’ll be able to see a little dribble of soap that lingers on the surface for a bit.
Trace will continue thickening from a light batter consistency to thick and gloopy. Work quickly or sometimes it will firm up inside your pan.
Note: If you do not use an immersion blender to mix your soap and instead opt for a spoon and/or whisk then expect your soap to take up to three hours to trace
Adding Ingredients at Trace
Once your soap has traced you’ll need to work quickly to add in some of the more delicate ingredients to your soap batter. These will include your superfatting oil, essential oils, and other extras. You add these after trace for a few reasons. First of all, the heat and process of saponification could destroy or use fragile ingredients, especially essential oils. Lye could even turn them into soap! So we add essential oils at trace to ensure they stay in your batch to scent your bars.
Also, if you add whole ingredients, such as rolled oats, 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 stick blender is set aside. The last reason specifically touches on the super-fatting of your recipe.
Most modern soap recipes include a super-fat, meaning an extra amount of oil. The lye in a recipe can only convert a certain amount of oil into soap. If you add more than it needs it stays free-floating in the soap. This oil makes your soap more conditioning and less harsh on the skin.
Most of my recipes do not include a super-fat step. I have the super-fat 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.
Adding a Super-fat at Trace
In the case that you have a fine oil that you’d like to act alone as a super-fat, it should be added at Trace. This gives it a better chance of surviving in your soap whole, rather than being converted into soap.
An easy way to super-fat is to add a liquid oil which you have measured and have set aside for this step. If you choose a hard oil, such as cocoa butter, you will need to melt it first before pouring it in. Personally, I’d recommend sticking with a liquid oil on your first few attempts.
Adding an antioxidant
Part of this step is adding your antioxidant if you’re using it. Some soap makers use them and some think they’re unnecessary. The role of antioxidants is to help keep free-floating oils in your bars from going rancid over time. There are three main antioxidants that soap makers use: Grapefruit seed extract (GSE), Rosemary Oleoresin Extract (ROE), and Vitamin E, and each has its own pros and cons.
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. Soap does not require a preservative since once it’s ready to use, it does not contain any water or environment where bacteria can thrive.
Note: Try to work as quickly as you can in this step since depending on your recipe, your soap may start to set (harden up). Also, I’ve found that using a whisk is the best way to incorporate your extra ingredients. However, try not to beat the soap or introduce air into the mix or you can end up with air bubbles in your soap.
Pouring into Molds
Your soap is now ready to be poured into your molds. Please have a look at the equipment post for more information on what you can use. For most of my soap, I use silicone loaf molds that hold 6-10 bars at a time. This one is my favorite. There are plenty of other types of molds out there though and quite a few household hacks though.
Lift and plunk your molds down a couple of times after the soap has been poured in to help settle out the mix and release any trapped air bubbles.
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 deepen the color and add slight transparency to the finished bars — this is called putting the soap through the ‘gel state’.
You can insulate your soap in a wooden box as I do, or line the top of the soap with cling film and wrap a big fluffy towel around the mold. The main way I insulate my soap is to over-process it. I’ll simply pop the soap into a cold oven overnight. For small batches, I’d recommend heating the oven just slightly before adding the soap. Make sure the oven is turned off afterward.
If you choose not to insulate your soap then the color will be much lighter and opaque. You can even ensure that your soap doesn’t gel by putting it in the fridge after you’ve poured it in the mold.
Insulating soap loaves
If you do not insulate your loaf molds there’s a chance that the inner part of the loaf will ‘gel’ and the outer parts will not. You’ll see this as a darker circle on the inside of your cut soap bars. It will not affect the soap’s usefulness but can look unattractive.
If you use sugars in your recipe it’s likely that you will not need to insulate your soap. Sugars will raise the temperature of your soap even after it’s been poured into the molds and further insulation can cause your soap to volcano or darken to an undesired color.
Wait 24-48 Hours
You need to let the soap sit for at least twenty-four hours before you unmold it. This allows for the soap to set and cool down to room temperature and if you try to take your soap out before this time then you can be left with a sticky mess. I actually recommend waiting a full 48 hours before unmolding. That way, saponification is pretty much complete and the soap is safer to handle.
Cutting your Soap
If you’ve used small bar-sized molds you can pop your soap out and set them on shelves to cure right away. Those using non-silicone plastic molds may encounter some issues in getting the soap out and in this case, I’d recommend popping the molds into the freezer for around thirty minutes to an hour. The soap should pop out like an ice cube afterward. I have a lot more information on soap molds over here.
With loaves, just use a sharp stainless steel knife, pastry cutter, or wire cutter, to cut your soap block into bars. 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 would be to use a miter box and a knife that will fit through one of the sets of vertical slats.
Curing your Cold Process Soap
Your soap looks finished and might even smell pretty nice at this point but it’s not ready yet. First, you’ll need to set the bars in a cool and well-ventilated area, out of direct sunlight. Space them out to increase airflow, and leave them to dry for at least four weeks.
This period is called ‘curing’ and it gives time for the soap to finish saponification. It’s also to give them time to dry and for the water to evaporate out of your bars. 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. For full instructions on curing soap, and ways to speed up the process, head over here.
Hopefully, this tutorial 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.
Natural Soap Making for Beginners Series