Part 4: Natural Soap Making for Beginners: Make, Mould, and Cure
How to make Cold-Process Soap
This is the fourth post in this four-part series on natural soap making.
The Cold Process Method is one of the most common ways to produce soap at home. It’s easy enough for most anyone to try and though there might be some uncertainty in your first attempt, you’ll get the hang out of it by the second or third try.
In this tutorial I’ll be showing you the steps I go through when making a honey soap though 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.
Assemble your Ingredients and Equipment
My stations include my warming area where I’ll melt the oils and I have my digital thermometer, spoons, an old kitchen towel and a mini strainer waiting at one side. On the other I have my stick blender assembled and plugged into the wall. I also keep my bowl of liquid oils and additional measured ingredients such as essential oils, herbs, and my antioxidant in this area.
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 cold water.
In between these areas I have my moulds sitting out and waiting as well as insulation materials such as towels and the wooden box I place my silicone moulds into.
Measure your Solid Oils
Once you’re organised, measure your solid oils using your kitchen scale. I ordinarily just measure directly into the pan I’m planning on heating them in. I don’t mix my solid and liquid oils at this point because the whole point of heating is to melt the oils into a liquid state and liquid oils are naturally liquid. Also, it takes less time to melt the hard oils then add the liquid ones than to mix them all together from the start.
Once your hard oils are measured and in a deep stainless steel pan, start heating them on the hob. I keep the heat on med-low and don’t use a lid. Keep an eye on the pan and break up any larger pieces of solid oils to speed up the melting process.
Making the Lye Solution
Once your hard 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 minimised. 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 requires lye, including the pre-made melt-and-pour bases you can find through specialty suppliers. It’s just that in melt-and-pour, the lye has already been combined with the oils for you in advance.
Measure your 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 and slowly pour the lye into the water and stir with a stainless steel utensil. The chemical reaction between lye and water produces a lot of heat so please be careful.
Please also remember to never pour the water into the lye since it can result in a mini explosion. Another important thing is to make sure that your water/liquid is at least at room temperature when you add the lye to it – this is especially important for those of you who are planning on making soap using a herbal infusion. If your water is even lukewarm your lye solution can start to boil violently and even volcano up and out of your container. This volcano action can also happen if you have any ‘sugars’ such as honey or milk in your liquids.
Another thing I’d like to recommend is to always measure your lye and water into separate containers. When I first started making soap I measured the lye directly into the water and though it seemed to work fine for awhile I had a few accidents that have impressed on me the importance of ‘Measure first, mix later’. The scariest soap making instance I’ve had was when the lye solution volcanoed while I was pouring lye into some lukewarm peppermint tea. I was especially unprepared for the situation because the jug was sitting on the scale and I was actively trying to measure lye at the same time as the solution was going crazy. Not good…so please learn from my mistakes.
Measure your Liquid oils
While your solid oils are still melting and your lye-water is cooling down, measure your liquid oils into a bowl. I’ve found that if you’re using powdered colours (such as Iron Oxides and Ultramarines) that this is the best time to add them to oils – a milk frother is the best way to disperse them throughout the liquid oils. If you opt to do this then your entire batch will be this colour which is perfect if you’re making a single colour soap.
If you’re planning on using more than one colour you’ll need to add it after the soap has traced. I won’t be covering that step in this tutorial since it will just get confusing with the photos. No doubt there will be another blog post from me in the future on creating multi-coloured soap!
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 the same temperature? The answer is in two parts.
First of all, the temperature you mix your soap at will affect how your soap comes out in both colour 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 mould, if sugars (honey, milk, sugar) are used, and what colour you hope your batch will turn out. The hotter the temperature, the more intense the colour. Personally I make soap when the oils are between 110-130F and err on the cooler side if I’m using sugars. If you mix cold-process soap over 130F then you risk a whole host of issues including volcano-ing, cracking, and discolouration.
The second part to mention is about lye temperature. Some soapers 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 is above the lowest melting point of your oils then you’re fine. If the lye solution cools your oils so that they begin to harden then you might run into an issue referred to as False Trace. You think your soap has saponified but it hasn’t. The oils have just gone solid again.
When I’m soaping I usually mix when the oils are between 110-130F and the lye solution is within 10 degrees of the oil’s temperature but under 130F.
For larger batches that are going into large moulds many soap makers tend to stick with lower temperatures around or below 100°F. This is because of the tendency for large batches of soap placed into a large loaf/block moulds to get and stay hotter in the centre than on the outsides and for the colour to change in some places as a result. Most soap makers that create large batches are doing so to sell them on to the public and a strangely coloured bar of soap is less marketable than one with homogeneous colour and texture. If you’re making a small batch of soap and want a deep colour 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 colour then stick with lower temperatures of around 95-100°F.
Having honey, milk, or actual sugar in your recipe will cause your soap batter to heat up to much hotter temperatures even after it’s been poured into moulds. If you plan on using these ingredients then consider using lower temperatures or the sugars can burn and caramelise resulting in a different smell and colour than you were hoping for.
A higher mixing temperature will mean that the colour of your soap will deepen dramatically due to a reaction called ‘Gelling’. If you’re after soft and light coloured bars then stick with lower temperatures. Please also read the section below on insulation since this will affect the colour of your soap too.
Combining your Oils and Lye Solution
Once your hard oils are fully melted, add your liquid oils, stir well, then check the temperature. Compare this against the temperature of your lye solution and adjust them until they’re within a degree or three of each other and your target mixing temperature. I’ve found that if the temperatures aren’t in the same range then your resulting soap will look and feel different, crumbly even. So make sure to keep them close.
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 stick 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 its reached a thin pudding-like consistency. Once you lift your stick blender out of the mix, you’ll also notice that you’ll be able to see little trails of soap that linger on the surface for a bit.
Note: If you do not use a stick blender to mix your soap and instead opt for a spoon and/or wisk 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, your antioxidant, and botanicals such as herbs and dried flower petals. You add these after trace for a couple of reasons. Firstly, the chemical process of saponification (the oils combining with the lye-solution) can be very hot and adding fragile ingredients during that phase can destroy and evaporate their beneficial and fragrant properties.
Secondly, if you add whole ingredients, such as rolled oats, before the soap has traced, then the stick blender will pulse them up too. The last reason specifically touches on the superfatting of your recipe. If you add your fine superfatting oils before saponification, then some of those oils will be converted into soap. If you add them after saponification, then they’ll stay in your soap as free-floating oils as intended.
An easy way to superfat is to stick with a liquid oil which you have measured and have set aside for this step. If you choose a hard oil, such as shea butter, you will need to melt it first before adding it into the soap. Personally, I’d recommend sticking with a liquid oil on your first few attempts.
Part of this step is adding your antioxidant. There are three main antioxidants that soapers use to help ‘preserve’ their soap: Grapefruit seed extract (GSE), Rosemary Oleoresin Extract (ROE), and Vitamin E, and each has their 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 Moulds
Your soap is now ready to be poured into your moulds. 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 moulds that hold eight bars at a time though there are plenty of other types of moulds out there and quite a few household hacks. Lift and plunk your moulds down a couple of times after the soap has been poured in to help settle out the mix and release any trapped air bubbles.
Now at this stage you have a choice on whether you’d like to insulate your soap or not. Insulating it will keep the temperature hot and steady which will deepen the colour and add a 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 mould. If you choose not to insulate your soap then the colour will be much lighter and opaque – much more like the soap you find for sale at the supermarket.
Note: If you do not insulate your loaf moulds 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.
Sugars note: 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 moulds and further insulation can cause your soap to volcano or darken to an undesired colour.
Either way you choose to insulate, you need to let the soap sit for at least twenty-four hours in the mould(s). 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.
Cutting your Soap
If you’ve used small bar-sized moulds you can pop your soap out and set them on shelves to cure right away. Those using non-silicone plastic moulds may encounter some issues in getting the soap out and to you I’d recommend popping the moulds into the freezer for around thirty minutes. The soap should pop out like an ice cube afterwards.
With loaves, just use a sharp knife to cut your soap block into bars. If you want exact sized bars then invest in a professional soap cutter – some are relatively inexpensive and good for the small producer. A hack would be to use a mitre 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, and away from direct sunlight, for at least four weeks. This period is called ‘curing’ and it gives time for the soap to finish saponification (which is generally the first two to five days) and for all the excess water to evaporate out of your bars. Just try to forget about the soap and move on to other projects for awhile. Before you know it, the time will have passed and you’ll have a full batch of lovely handmade soap to try!
Hopefully this tutorial has been helpful but 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 as well.