Making Soap

After some consideration, I have decided to include my adventures in soapmaking here on this blog. I contemplated whether it would be better as a separate topic, or on my own personal blog, but I have decided that it really fits better here. I want to make my instructions here suitable for the complete novice, so I will be introducing the basic concepts and terms, including the underlying science. We will go from understanding the basic process to how to develop your own recipes, and we will see some sample recipes along the way.

Basic Chemistry

Ok, I am going to start with some basic soapmaking chemistry. If you are not interested in the chemistry, you can skip over this section, but if you are curious I will try to break it down for the lay person and it will probably help you understand the soapmaking process better.

The two key ingredients in soap are fats and lye. The fat could be a vegetable oil (like olive), or an animal fat (like lard or tallow), or a “butter” (like shea butter), or a blend of these. But all of these fats are basically composed of triglycerides. Each molecule of fat consists of a glycerol (glycerin) with three fatty acids attached. These fatty acids all have carbon chains of varying length and it is the variation in these fatty acids that contributes to different properties in your soap from different fats that are used. We are all familiar with the basic properties of these compounds — they are slick and oily, they do not mix with water and they can adhere to fabrics and be difficult to wash off the skin. Basically the opposite of what we want in soap! In fact, the main purpose of soap is to wash away oily or hydrophobic substances that can not be readily washed away with water.

It is the next key ingredient that resolves this ironic dilemma. Lye is a strong alkali or base, either sodium hydroxide or potassium hydroxide. Chemically, you can think of it as the opposite of an acid. It is very reactive and used in a huge variety of applications. The reactive nature of lye makes some people scared of it, and of products made with it. But remember that table salt is composed of sodium — a reactive metal that bursts into flames when exposed to water — and chlorine, which is a toxic gas. Yet table salt shares neither of these properties and is safe to consume (in moderation). Similarly, lye is used to make bagels and olives, and even to balance the pH of eye drops, yet all of these things are quite safe. Similarly, properly made soap is also quite safe. Indeed, you can not make soap without lye (most people who claim to do so are either using a pre-made soap base that was made by reacting the lye and fats before they got it, or else synthetic detergents which are not soap at all).

The lye actually splits the bond between the glycerol and one of the fatty acids. Since there are three fatty acids in each triglyceride, it takes three molecules of either sodium hydroxide or potassium hydroxide to split them all off. One of the products of this reaction is glycerin. Although glycerin is nice and moisturizing to the skin, it is not the main product we are after in soap making. The other product is salts of the fatty acids. What I mean by forming a salt of the fatty acid is that the end of the fatty acid that was previously attached to the glycerol is now negatively charged and ionically bonded to a positively charged ion (either sodium or potassium, depending on the lye used). In this way, it actually is similar to table salt where the sodium and chlorine are attracted to one another because the sodium is positively charged and the chlorine is negatively charged (called chloride). They are not bound together by shared electrons like organic molecules, so they can separate when dissolved in water, but are attracted to one another like magnets.

Now, here is where the magic happens. What makes water different from oil is that it has a slight negative charge on the oxygen and a slight positive charge on the hydrogens. The opposite charges are attracted to each other like magnets! This is called being polar (think of the poles of a magnet). But since oil has no such charges for the water to be attracted to (it is non-polar), it simply gets pushed out of the way as the water molecules are drawn to each other. But these salts of fatty acids are a different beast altogether. The long carbon chain is basically non-polar and thus hydrophobic — it is drawn to oil and not water. But the other end has an electric charge, so it is hydrophilic — drawn to water. So the hydrophobic carbon chain embeds itself in oil that is adhered to fabrics or our skin, but the polar end is drawn to the water and so it pulls the oil into droplets in the water, surrounded by the hydrophilic ends that are now facing outward to interact with the water. So this dual nature of these salts of fatty acids is what allows us to wash away oily substances with water and this is the essence of what soap is.

Now, there is one more important ingredient in making soap: water. The water does not participate in the soap making reaction (which is called saponification, by the way), it is used merely to dissolve the lye. However, the amount of water can have a big influence on the soap making process. We will learn more about this role as we get into the actual process of soap making. Obviously, the water we are dissolving our lye in does not readily mix with fats, so vigorous mixing is required initially. But remember that soap has a way of bringing these two very different components together, so as the reaction begins the soap that is forming will begin to stabilize the mixture.

Now, that we have gotten a basic understanding of the chemistry behind soap making, I think we are ready to get into the actual process.

Equipment

The first step is, of course, to assemble all of our equipment and make sure we have everything we will need in the process ready, so let’s begin by going over exactly what equipment we will need.

Almost all recipes will measure most or all ingredients by weight, so we will need a scale. An ordinary kitchen scale will do. I prefer one that measures grams because it is more precise, but a lye calculator will generally give you measurements in both grams and ounces. You may sometime find additives measured in teaspoons or tablespoons “ppo”, which means “Per Pound of Oil”, so you may use ordinary measuring spoons for this. You may also find measurements for fragrances or essential oils in ML, for which you can use a syringe or graduated cylinder.

You will also need containers for all of your ingredients. The containers that you use to measure your lye, to mix your lye solution, and to mix your lye solution with your oils, must all be lye safe. So what materials are acceptable for this? Your best options are plastics HDPE ♴ and PP ♷ or stainless steel. Other plastics may buckle under heat, become brittle, or break down in the presence of lye, so make sure you check for the appropriate recycling codes. Aluminum reacts with lye, so make sure that you have stainless steel and not aluminum. Glass can be used, but with caveats. Ordinary glass (soda lime glass) is gradually etched by lye and can shatter due to thermal shock or break when you accidentally tap it with steel spoon while stirring. Glass is not the most preferred material, although you will see soap makers using it in videos online, for these reasons. If you want to use glass, borosilicate has good resistance to lye, as well as to thermal and mechanical shock. Lab glassware is often made of borosilicate. Even borosilicate will eventually etch and should be replaced when you see visible signs of etching. The older PYREX was made of borosilicate, but the newer pyrex (note the capitalization) is not, leading to considerable confusion.

You will also need utensils for mixing. I like using a silicone spatula to scrape oils out of the container I weigh them in, and for scraping soap batter out of the container it is mixed in. Stainless steel spoons are also good for mixing and scooping. A stainless steel whisk may also be helpful for mixing in certain additives.

Then you will need some kind of mold to pour the soap batter into to saponify and harden. There are many options for this. You can purchase loaf molds that make a long “loaf” of soap to be sliced into bars. These are commonly made of wood or acrylic or silicone, or they may be wood with a silicone liner. If you use a wooden mold that does not have a silicone liner, you will need to line the mold with freezer paper or wax paper. You can also get silicone or plastic soap molds that have individual cavities for each bar, in a variety of shapes. A silicone baking pan can be used as well. Other options include any container that is made of a lye safe plastic, or even an empty Pringles can!

The last thing we will need is a way to slice the soap, if we did not use molds with individual cavities. You can buy a variety of sophisticated soap cutters, but you can also cut soap with an ordinary large kitchen knife, or a wire cutter like a cheese board. Wire tends to make cleaner cuts than blades, so I recommend a wire cutter if possible.

The Soapmaking Process

The first step is to separately combine all of your oils in one container and your lye solution in another. (Well, unless you count formulating your own recipe with a lye calculator, but I will save the details on that for another post.) In order to combine your oils, you will want to melt those that are solid (such as coconut, lard, tallow, shea butter, etc). I like to use a stainless steel bowl nested in a pan of water on the stove top, but you could use a stainless steel pot directly on the stove top or a Crock-Pot, etc. You just want to melt the oils. Of course, you will weigh each oil before adding it to the common pot, so you will need a separate container for weighing them in. The hotter your oils are when you add the lye solution, the faster it will move so you may want to let them cool a bit before adding the lye. (By contrast, if you try a Castile recipe this soap moves so slowly that you will want both your oils and lye hot and may even keep the heat on until the soap traces, which we will discuss shortly.)

To make your lye solution, you will first weigh both your water and your lye separately. This is the stage where you will need to exercise extra caution as the lye is very caustic. You may want to wear gloves, eye protection, even an apron, to protect yourself from spills and splashes. You always add the lye to the water, never the other way around. Some say to remember that it snows on the lake (it never lakes on the snow). The general rule in chemistry is that you add the more reactive substance (lye) to the less reactive (water). The dissolution of lye produces a lot of heat, and if you pour water on the lye it could heat so rapidly that the water begins to boil, causing the caustic mixture to erupt in your face. If you are using delicate liquids like milk for your lye solution, you will want to keep the temperature down to avoid scorching. You can actually freeze the milk and you can nest your lye container in an ice bath. Add the lye slowly and stir it into your liquid. If it is very hot, you may want to let it cool a bit before adding it to the oils. (Again, if you are making Castile, you may actually want to add the lye while it is still quite hot because it tends to move so slowly anyway.) Remember not to test the temperature with your finger, the lye solution is caustic!

Once both your oils and your lye solution are ready, it is time to combine them. Pour your lye solution into your oils and then blend them using a stick blender (sometimes called an immersion blender). It is possible to make soap without a stick blender, of course, but it may take a very long time. To avoid overheating and destroying your stick blender, use it intermittently, maybe 10-15 seconds at a time. You can stir in between with a spoon, whisk, or spatula. Initially, the lye solution will sink to the bottom, but once you begin blending the mixture will take on a more opaque or milky appearance. Generally what you are looking for at this stage is for the soap batter to begin to thicken. This is called tracing. At a light trace, you can just see the pattern if you drizzle soap batter across the surface. As the batter progresses to a medium or thick trace, it will begin to take on a more pudding-like consistency. If you were trying to make patterns or swirls with two or more colors, the pudding-like consistency of thick trace would be too thick to work with, but for a basic beginning recipe it will be fine if your batter is on the thick side. Actually, it is not necessary to even bring the batter to trace as long as it forms a stable emulsion. Soapers often do this when they are working on intricate swirls and such, but it can be difficult for the beginning soap maker to tell when it has reached this stage and you don’t want your soap to separate in the mold.

Once your soap batter has reached the right consistency, you are ready to put it in your mold. (The process I am describing here is cold process, which I recommend for beginners. If you were making hot process, you would continue cooking it until saponification was complete, but I will save that topic for another post). This is also generally when you would add your scent, just before putting it in the mold. Other additives, like activated charcoal or clays, are also commonly added at trace. Many colors can also be added at this stage (multi-colored soaps are often made by dividing the batter at this stage and adding different colors to each portion), though others need to be infused in an oil or put in the lye solution. But for a beginner recipe, we can simply put the soap in the mold.

At this point, the soap needs time to finish saponifying and set up. As the soap saponifies, it continues to produce heat. As it does so, the soap may take on a translucent quality. This is the gel phase. Many soap makers insulate the soap (with a towel, for instance) to ensure that it gels fully. If the soap is kept cool enough, it is possible to avoid the gel phase. Sometimes this may be desirable, but what we want to avoid is a partial gel. If the soap gels in the center, but not all the way out to the edges, there will be a difference in the coloration when the soap is cut. This is a purely cosmetic issue (the soap is perfectly safe to use), but generally considered undesirable. If the batter is warm enough when it is poured, you might not need to take any steps to ensure complete gelling. It may also suffice to put the mold in a warm place. The soap needs to sit at least over night and perhaps longer. At this point, you just want to make sure the soap is firm enough to cut.

Now you will need to take the soap out of the mold. Some molds have sides that come apart to make this easy. If you used a Pringles can, you can either tear it apart and peel it off, or try to get the soap slide out. Giving it some extra time to allow the soap to lose some moisture and draw away from the sides may make it easier. You can also put the soap in the freezer before trying to remove it. Once the soap is out of the mold, you will will want to cut it into bars. I recommend a wire cutter, if available, but a knife will work.

It may seem like the soap is finished at this stage, but it is not. The soap should be safe to use within 24-48 hours as saponification will be complete and there will be no lye left to burn the skin. But this soap will melt quickly and not have a desirable texture or lather. Soap typically needs to cure for at least 4-6 weeks to develop these desirable qualities. During this time, excess water is evaporating and the soap develops a crystalline structure inside. The soap will lose weight, fairly rapidly at first, then taper off. This is where patience comes into play. You can try a bar early, if you want. But please give your soap the time it needs to cure properly. After all, what is the point of going to the trouble of making it yourself, if you are not going to put in the time and effort to produce something of superior quality? All it needs at this stage is to be stored in a dry place. Separate the bars so that air can circulate between them. A rack that allows air to circulate under them is desirable as well.

Recipes

Now that you understand the process, let’s take a look at how to formulate a recipe. I am not going to get into all of the math here, instead we will use a lye calculator. You can plug in some basic information, like the total size batch you want, the amount or percentage of each oil you want to use, the desired lye concentration, and the superfat, and the lye calculator will give you the amount of lye and liquid (as well as the amount of oils, if you gave it percentages as I normally do). I recommend Soapee. It is a free, online lye calculator that allows you to save recipes. (If you want to be able to share your recipes, make sure you sign up with a social media account.) You will notice that the steps are numbered, so let’s take them one at a time.

1 - Liquid or Solid soap recipe?

This one is really simple. We are making solid soap using NaOH. 

2 - Select recipe units of measure

I like to specify the oils in my recipes in percentages because this makes comparison between different size batches very simple and recommended usage rates are typically expressed in percentages as well. But for the total batch size, I like to use ounces or pounds because this is the common weigh of expressing the size of a mold, based on the pounds of oil in a batch that will fill it. A Pringles can holds about a 24 ounce batch.

3 - Amount of water in recipe

Here is one case where I feel the default leads us astray. I do not recommend using the “Water as a percent of oils” setting at all. (Read “Understanding Water Discounts and Lye Solution in Soap Making” on modernsoapmaking.com to understand why.) Use lye concentration or water to lye ratio instead. These two options are equivalent, they are just expressed differently. For the beginner, I recommend starting with 2:1 or 33% lye. The lowest you can safely go is 1:1 or 50% lye, and you will see this is what I use for the Castile (100% olive oil) recipe. If you wanted to do intricate swirls, etc, you might want to use more water so that the soap moves slower, giving you more time to work with it.

4 - Oil superfat

For soap that is used on skin, you generally want at least 5% superfat. This is because one of the purposes of the superfat is a margin of safety, to ensure that your soap does not wind up lye heavy. This can happen due to minor errors in measurement and natural variations in the saponification values of the oils (the amount of lye needed to turn them into soap). If there is excess lye after all of the oil is saponified, the soap will be harsh and can burn your skin. A higher superfat can also make a soap that is strongly cleansing (potentially harsh and drying) milder, which is why you will see that the 100% coconut oil recipe uses 20% superfat. This, however, is an exception, not the rule. Most soaps will have only 5-7% superfat, perhaps as high as 10-11%, but not 20%. You will notice my basic recipes are 7%, while the Castile is 5% (pure olive oil soap is already very mild). Another exception here would be a laundry soap, which might have only 0-1% superfat (if it is a bit lye heavy, that is ok because it is not meant to be used on your skin).

5 - Fragrances

We won’t really bother with this one for now. It only gives a suggestion on how much fragrance to add, but this varies depending on what fragrance you are using. Essential oils, especially, each have different recommended usage rates, and if you are using several in combination you may not even find this feature very useful. It does not, however, affect any other aspect of the recipe. You can set it to 0 if you like, or just ignore it when you make the soap, nothing else will change. If you use a fragrance oil, make sure you check the recommended usage rate from the manufacturer.

6 - Select Oils

This is really the main thing that sets a recipe apart. When you select an oil from the list, you will see a box pop up to the right showing the properties of that oil, including its fatty acid composition and “properties” like bubbly, cleansing, etc.

The “properties” in your soap calculator are really just a way of grouping together fatty acids that have similar properties. The fatty acids that make up the oils in your recipe are the main factor in determining the qualities of your finished soap. For instance, saturated fatty acids with shorter carbon chains (like lauric and myristic acid) produce a soap with a stronger detergent action, so these count toward the total “cleansing” percentage, as well as “bubbly”. They make a soap that is better at cleaning and stripping away oils and produces a bubbly lather. Saturated fatty acids with longer carbon chains (like palmitic and stearic acid) make a soap that is less soluble and thus last longer, so these count toward the “longevity” percentage, as well as more “stable” lather with a creamier texture. Both contribute to the “hardness” of the bar.

Unsaturated fats (such as linoleic, linolenic, and oleic) contribute to the “conditioning” property of the soap. Unsaturated fats tend to make a mild and gentle soap. However, these oils are prone to rancidity, which can manifest as Dreaded Orange Spots or DOS in a finished soap. The best measure of this is actually not the “conditioning” property, but the iodine value. This is a measure of the total number of places that the fatty acids are unsaturated (some fats — polyunsaturated fats — are missing more than one pair of hydrogen atoms), and each of these places is a point where an oxidation reaction can occur, leading to rancidity.

Ricinoleic acid, found in significant amounts only in castor oil, is unique. It is an unsaturated fatty acid that also has a hydroxyl group on the carbon chain. In soapmaking, it enhances and stabilizes lather in small proportions. It contributes to both the “bubbly” and “stable” properties, but not to “hardness” or “cleansing”. It is also considered to be part of the “conditioning” property.

Note that the recommended ranges for these properties are only suggestions or guidelines. You may prefer a soap that is less cleansing and therefore milder. These numbers are also based only on the proportions of the fatty acids in the oils that you are using and will not take into account other factors. For instance, the 100% coconut oil soap would appear to be very cleansing, and thus potentially harsh and drying. But the higher superfat makes it milder and the “properties” of your recipe does not take the superfat into account, only the proportions of the fatty acids in the oils.

Once you have selected an oil, you can click on the plus button at the upper right of either box to add it to your recipe. Another box will appear further to the right with a list of all oils in your recipe. Here you can type a percentage for each one (or whichever unit you selected). As you do this, the full recipe will be generated (and continuously updated for any changes) below. You will be able to see the properties for your recipe as a whole as well, along with the recommended ranges.

Below this, you will have an option to input a name, description, and notes. You can even include pictures. Then you can save your recipe, print it, share it, etc.

Now that you have a basic idea of how to use the lye calculator, let’s take a look at a basic recipe as an example:

Grocery Store Soap

I call this recipe “Grocery Store Soap” because you can typically find the ingredients at the grocery store. This is also the recipe I used in my instructional video. For this recipe, you will notice that the properties mostly fall within the recommended ranges. The cleansing is on the low end, making this a fairly mild soap. The coconut oil is the main contributor here, so if I wanted a stronger cleansing soap I could use more coconut oil and if I wanted a very mild soap (some prefer cleansing below the recommended range or even down to 0) I could reduce the coconut oil even further. If I wanted a harder and longer-lasting bar, I could increase the lard, substitute tallow, or add a harder oil like cocoa butter.

It is also sometimes helpful to consult other sources regarding the recommended usage rates of your oils. For instance, castor oil should not be used at more than about 5-10% in a bar soap. Too much castor can make your soap rubbery and will not actually give you the bubbly lather you expect. This is a case where the numbers in the lye calculator can be misleading. Castor oil contributes to the bubbly property, so you would expect a 100% castor oil soap to be very bubbly. But it is not, it actually produces little to no bubbles. A small amount of castor helps to boost the lather, but more is not necessarily better in this case.

For simplicity, you might want to start out by trying a single oil soap recipe. Not all oils are suitable to use at 100%, but I have a few examples here using the same common ingredients used in my “Grocery Store” soap.

Castile

This is a traditional soap made with 100% olive oil. You will notice that for this recipe I reduced the water to 1:1. This is because olive oil is slow to trace and to cure. The water discount helps to speed things up a bit. Even for a beginner, this recipe should not move too fast. In fact, it may still take a long time to trace. I also cut the superfat back down to 5% because this soap is already very mild. You will notice the bubbly and cleansing properties are both zero. This does not, however, mean that it will not make any bubbles or that it will not clean. It just does not have any of the fatty acids that contribute most to those qualities, so it will be very mild and not very bubbly. This soap will also be harder than the numbers might suggest. The other big difference to note with Castile is that it needs a very long cure time, probably a year or more. Otherwise, the soap will have an unpleasant slimy texture. Many people, however, love Castile soap and consider it worth the wait.

Lard Soap

You will notice that a 100% lard soap is surprisingly balanced. All of the properties are in the recommended range except bubbly and cleansing. This also makes a very mild soap. The stable property indicates a stable, creamy lather. So while it will not make big fluffy bubbles like coconut oil produces, it will lather but with much smaller bubbles and a creamy texture. You can make a similar soap with just tallow, it is harder and longer lasting, a bit more cleansing and bubbly, but not as conditioning as lard. However, tallow is generally harder to find.

Coconut oil soap (20% superfat)

This soap is another exception to the rules. The cleansing is very high which would tend to be harsh and drying. But the unusually high superfat balances this, making the soap milder on the skin. You will notice that the hardness is very high, but the longevity is low. This will make a hard soap, but it will melt fairly quickly and not last very long in the shower. Hard soaps tend to last longer, but coconut oil is again an exception, making soap harder but not longer lasting.

To help you get a better idea of how the process actually works, I also made a video of making a basic grocery store recipe. You can watch it here:



At this point, you have several recipes to try and you should have enough of an idea of how the lye calculator works to begin tweaking your own recipes. You can adjust the proportions to suit your own needs, or add other ingredients like shea butter, etc. Hopefully, this give you a good introduction to the world of soapmaking.