Knowing how soap is made and the science behind it will help you be alert to pitfalls, troubleshoot problems, develop your own recipes, and keep yourself safe during the process. This book primarily focuses on cold-process soapmaking. The term “cold-process” refers to the fact that you don’t need to use an outside heat source, such as a stove, during the mixing stage of making soap, although heat is produced during the process. This is because lye mixed with water undergoes an exothermic reaction that can produce temperatures up to 200°F (93°C).
The formula for making soap can be written like this:
Triglycerides (fatty acids) + Sodium hydroxide
= Soap + Glycerin
In plain English, oils react with lye to create a solid mass. Oils are made of triglycerides, three fatty acid chains connected with a glycerin molecule. Linoleic acid triglycerides (an essential fatty acid commonly found in soapmaking oils) interact with sodium hydroxide (lye) in a process called saponification. The result of saponification is soap with a small amount of glycerin mixed in.
Sodium hydroxide is typically sold as a powder or flakes. It requires a carrier agent to dissolve it so it can mix with oil. Soapmakers typically dissolve their lye in water, but other liquids may be used.
When lye is added to water, an exothermic (heat-producing) reaction occurs. When substituting other liquids for water, the reaction is often hotter, causing other reactions. For example, lye causes the proteins and sugar in milk to scald, turn yellow, smell badly, and congeal into a thick soup, all of which is normal. Each recipe in this book discusses what to watch out for when soaping with alternative liquids and how to control or minimize problems.
Different oils require different amounts of lye to turn them into soap. The amount of lye needed to turn a specific amount of oil into soap is called the saponification (SAP) value (see What Is the SAP Value?). Oils are composed of strings of short- and long-chain fatty acids. Palm oil, for example, contains five main fatty acids while coconut oil has eleven, and olive oil has six.
Those fatty acids have different properties that dictate the amount of lye necessary to turn the oil into soap. For example, palm oil is made of over 40 percent palmitic acid, a saturated fatty acid that makes palm oil solid at room temperature. Olive oil, however, contains up to 83 percent oleic acid, which is liquid at room temperature. Palm oil acts radically different than olive oil when mixed with sodium hydroxide, and the two oils require different amounts of lye to turn them into soap.
Fatty acids are also what give the final soap its different characteristics. For example, coconut oil promotes lather, while avocado oil is typically used to add nourishing characteristics to soap. Meadowfoam oil and mango butter both contribute conditioning and moisturizing properties, but the fatty acids in meadowfoam oil produce creamy bubbles while mango butter does not provide much lather.
The recipes in this book have all been carefully formulated to ensure a properly balanced bar of soap. If you are just starting out, it is best to follow all of the recipes exactly to get a feel for the process and what a good bar feels like. See chapter 7 to learn more about formulating your own recipes.
Soap works by laying down a slick of soapy lather that attaches to dirt. Both the lather and the dirt are rinsed away by water, but this process can also strip the skin of its natural oils and moisture. Extra oil in the soap can help to replenish the skin’s natural oil barrier, making it feel moisturized.
This is why many soapers choose to leave a percentage of extra oil in their soap, a practice called “superfatting” or “lye discounting.” A recipe that calls for the exact amount of lye necessary to convert all the oil into soap is said to have a zero percent lye discount or to be zero percent superfat. A bar that is zero percent superfat — meaning it has no excess oil after saponification — will be a stable, hard bar of soap, but it is likely to be somewhat less gentle to skin.
The downside of incorporating extra oils is that they can weigh down lather, decrease shelf life, and make a softer bar of soap that does not last as long in the shower. Superfatting is a personal preference. Most soapers choose to keep their superfat, or lye discount, to 10 percent or under. This book uses superfats between two and seven percent.
In addition to calculating the amount of each oil used in a given recipe, you also need to know how much water (or other liquid, depending on the recipe) is needed. The water acts as a carrier for the lye by forming ions that react with the oils. You need to use enough water to fully dissolve the lye, but not so much that it creates a sloppy bar of soap. Most calculators call for a range of water amounts, typically between 33 and 39 percent of the total amount of oil.
Using the maximum amount of water generally gives the best results. Using less water than the recipe calls for is called “water discounting.” Soapers water-discount when they want to hasten the drying and curing time but still produce a hard bar of soap. If you use less water than the recipe calls for, your soap may reach trace more quickly than if the full water amount is used. If your soap becomes too thick too quickly, you will not have time to create elaborate designs. Water discounting is an advanced technique (see What Is a Water Discount?), best left until you have extensive experience soaping.
Kevin Dunn, professor of chemistry and author of Caveman Chemistry, has determined that the bulk of the saponification reaction is finished in the first 24 hours. This does not mean, however, that you should use your soap within the first day.
Once soap has been unmolded and/or cut into bars, it must be set aside to cure and dry for four to six weeks in a well-ventilated area, turning bars every few days so that they dry evenly. This means if you make soap on January 1, your soap will not be ready to use, give away, or sell until January 29 at the earliest. During this period, the soap becomes more mild as the last traces of lye saponify and the bars lose weight as moisture evaporates, increasing hardness. This is important because a harder bar lasts longer in the shower.
The full cure time also helps to ensure that the lather of the bar is stable and long-lasting. Freshly made soap produces small, weak bubbles. Finally, if you are selling your soap, curing bars for the full time period is important to ensure that the final weight of the bar is correct and matches the label.
Acceleration. When the soap thickens quickly as the oils and lye-water are mixed. Often caused by components of fragrance and essential oils, it sometimes happens so fast the soap seizes up and is difficult to get out of the mixing bowl and into the container.
Alkali. A strong base is required to saponify fixed oils. Sodium hydroxide (lye) dissolved in water is the alkali used to make bar soap. Potassium hydroxide makes liquid soap.
Cold-process. A soapmaking method that uses the heat created by the chemical reaction from mixing fixed oils, such as palm or olive, with lye.
Cure time/curing. Most soaps should cure for four to six weeks after unmolding before being used. Curing allows water to evaporate, contributing to bar hardness and longevity, and often a milder final product.
Fixed oils. Nonvolatile plant or animal oils comprising triglycerides and fatty acids. At room temperature they can be liquid or solid.
Gel phase. An optional phase in cold-process soapmaking where extra heat is produced to increase color vividness or bar hardness. Some fragrances and essential oils can cause gel phase without extra effort.
Hot-process. A method that, like cold-process, mixes oils and lye but also involves an external heat source. Hot-process soaping often utilizes crock pots or ovens as heat sources and the soap is fully neutralized once it has hardened. Liquid soap is also made this way.
Lye discount or superfatting. A reduction in the amount of lye called for in order to leave unsaponified oils in bar soap to provide extra moisturizing properties. The standard range of superfatting is between 2 and 10 percent.
SAP (saponification) value. The amount of alkali needed to saponify a quantity of fixed oil. Each oil has a unique number, usually the average of a range.
Saponification. The chemical reaction between triglycerides in fixed oils and an alkali solution. The alkali solution breaks the triglyceride into fatty acid salts — what we call soap — and glycerin.
Soda ash. A white, powdery film of sodium carbonate that can form on soap when the lye and water react with carbon dioxide in the air, instead of the fixed oils in the soap. It is easily wiped off or rinsed away.
Ricing. Caused by the addition of fragrance or essential oils that are not compatible with the soapmaking process. Sometimes accompanied by acceleration, ricing is different in that it creates small individual clumps of soap that look like rice granules. In cured soap, it can leave pock marks and oil pockets.
Trace. The consistency of soap batter that signals emulsification of ingredients. It is identified by gently “tracing” a drizzle of batter on the surface; if the drizzle remains visible, the soap is said to be “at trace.” Trace can range from thin (melted milkshake) to thick (pudding). Typically, colors and scents are added once trace is achieved.
Water discount. A reduction in the amount of water called for in a recipe in order to shorten the curing time and prevent soda ash. Typical water discounts are between 5 and 15 percent of the total. Reducing the water amount can accelerate the recipe.
It takes a powerful alkaline agent to turn oils into soap. For bar soap, this agent is sodium hydroxide, a common chemical that is found in any number of other applications, from cleaning drains to making face creams (even making pretzels, which are boiled in lye-water before baking!). Lye has an extremely high pH of 14.0. By comparison, lemon juice has a pH of around 2.0 and human skin has a pH of 5.0 to 6.0.
Lye is caustic! It will burn skin, stain clothing, take the finish off wood, and damage many other surfaces. It can cause blindness and may be fatal if swallowed. Serious safety precautions must be taken when working with it, especially when it is dissolved in water.
A splash of lye-water will eventually eat through clothing and into your skin, leaving red marks and open sores. If you do spill lye-water on yourself, immediately remove contaminated clothing, including shoes, and wash your skin under cold running water for at least 15 minutes. (See Emergency Response below.)
Many soapers keep vinegar on hand, believing it neutralizes lye burns. There is some controversy in the soapmaking community about washing lye burns with vinegar rather than water. Adding vinegar (an acid) to lye (a base) creates a chemical reaction that releases more heat. Additionally, the act of putting vinegar on a lye burn hurts. Just use water.
Although vinegar should not be used to treat lye burns on skin, it can be used as precaution during the cleanup process. A quick wipe of your workspace with a vinegar-soaked rag can neutralize any lye dust that may have gotten on the surface.
When working with sodium hydroxide, it is very important to follow these safety guidelines.
Never soap with small children or pets in the room. Make sure they are adequately supervised so that you can give your full attention to your soapmaking process. It takes only seconds for a painful or debilitating accident to occur.
Avoid letting your soapmaking ingredients come into contact with aluminum, including containers, mixing utensils, and molds. It will ruin your soap and, worse, produce highly flammable hydrogen gas as a by-product.
Soap utensils are for soap. Food utensils are for food. Do not interchange soapmaking tools and food tools.
Skin. If you splash lye, lye-water, or fresh soap batter on any part of your body, immediately rinse the area with copious amounts of cold water. Then rinse some more, using fully cured soap to wash away the chemical residue. If you spill a large quantity on yourself, strip off your clothing at once and jump into a cold shower for 20 minutes, again using soap to clean off the lye. If your skin is red or painful after that, go to the emergency room.
Eyes. Immediately flush with cold, running water for at least 20 minutes. Seek medical attention promptly.
Throat. If you somehow swallow lye in any form, rinse your mouth thoroughly and then drink one or two large glasses of water. Do not induce vomiting. Seek immediate medical attention or call the American Association of Poison Control Centers at 800-222-1222.
Saponification (SAP) values are expressed as the milligrams of potassium hydroxide (a slightly different version of lye used for liquid soapmaking) needed to saponify 1 gram of oil. Since exact fatty acid and triglyceride content of oils can vary from crop to crop, a range of SAP values is most often given. Since sodium hydroxide is used instead of potassium hydroxide to make bar soap, the original SAP value has to be converted for use in bar recipes.
Divide the potassium hydroxide SAP value of each oil in a given recipe by 1,402.5 to get the sodium hydroxide SAP value. Then add those SAP values to determine the total amount of lye needed.
The calculation looks like this:
Potassium hydroxide SAP value ÷ 1,402.5 = Sodium hydroxide SAP value
Typically either the average value in the SAP range or the lowest value is used; this example uses the low value. Here is a very simple soap that uses 1 ounce of each oil:
Coconut oil 250 ÷ 1,402.5 = 0.178
Palm oil 202 ÷ 1,402.5 = 0.144
Olive oil 188 ÷ 1,402.5 = 0.134
0.178 + 0.144 + 0.134 = 0.456 ounces of lye
Fortunately, you don’t have to all this math by hand, as easy-to-use lye calculators are readily available online. See Using a Lye Calculator, below.
The good news is that you never have to do soapmaking math by hand if you don’t want to. There are a number of free lye calculators on the Internet that will calculate all your recipes with the click of a few buttons. Though they vary a bit in process, in general you enter the amounts of the oils you want to use, choose your preferred superfatting level, and click “Calculate” to get the correct amounts of water and lye needed for that recipe.
Some popular lye calculators are found at:
www.brambleberry.com, www.the-sage.com, and www.summerbeemeadow.com. Many of these calculators allow you to resize recipes as well as formulate your recipes by percentages. There are also lye calculators available for smart phones.
Caution: Some lye calculators offer the option to create liquid soap recipes. Make sure that you are calculating for bar soap. Liquid soap uses a d making ifferent form of lye (potassium hydroxide or KOH) and calls for different lye amounts. If you accidentally make bar soap using a liquid soap recipe, your soap will be lye heavy, it extremely drying for skin or even dangerous to use.
