Guest Post: Chemistry of Soapmaking

-- by Renee Williams

(Editor's Note: This article was submitted for our writing contest.)

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In the first installment of this series, we talked about necessary equipment. Today’s installment will go over  basic chemical processes of soap making, and some of the most commonly used ingredients to achieve the best results.

For Science!

Soap, according to the FDA (federal Food and Drug Administration) and taken straight from their website (as of 10/3/2014), is as follows:

[...] the Food and Drug Administration interprets the term “soap” to apply only to articles that meet the following conditions:

(1) The bulk of the nonvolatile matter in the product consists of an alkali salt of fatty acids and the detergent properties of the article are due to the alkali-fatty acid compounds; and
(2) The product is labeled, sold, and represented only as soap.

What this means for us – as consumers, DIYers, hobbyists, and preppers/off-grid folks – is that soap is the solid formed when a fatty acid (lard, coconut oil, olive oil, Crisco, butter, etc.) is mixed with an alkali (Sodium Hydroxide or Potassium Hydroxide) to create a chemical reaction.

Chemistry

When lye and fats meet in the pot, the lye breaks the chemical bond between the glycerin and the acid chains. The sodium in the lye replaces the glyceride, leaving you with two compounds, bound together in a matrix: Soap (that salt precipitate the FDA mentioned) and Glycerin (and of course excess water which eventually evaporates out).

Soap is a chemical by-product. It is formed when an acid – in our case, the acid chains that are part of any fat – meet and react with a strong alkali, such as sodium hydroxide (NaOH.) Many of you will be familiar with sodium hydroxide in its most commonly used form: drain cleaner.

Alkalis

For years, you could walk into any grocery or hardware store and buy a bottle of Red Devil Lye. These days, all of the commonly sold drain cleaners are not straight lye. Finding pure NaOH can be tricky a lot of the time now. There are websites where you can order it, or if you happen to run a business you can frequently locate chemical supply houses that will sell it to you once you show them your tax ID and/or any state licensing that your area requires. Later on, I’ll do a follow-up to this article on how to process your own lye solution from wood ash and rainwater; but for now, do yourself the favor of starting out with a pure ingredient. Using the pure ingredients we have available to us currently – and having a good grounding in how those ingredients react and set up – will give you a good understanding of how the ingredients are supposed to react, and will save you a lot of confusion and head scratching in a SHTF situation where ingredient purity can’t be guaranteed and you're having to improvise

Fats

Fats – both solid fats like butter, lard, and cocoa butter, and liquid fats like olive oil, corn oil, soybean oil, or sunflower oil – are composed of two basic parts. The first part is a Glyceride molecule, or glycerin. This is what will give the soap its “slippery” feel when it’s finished.

The second part is an acid chain. Each glycerin molecule has room for up to 3 acid chains to be attached. Some fats use all three slots for acid chains; others do not, which gives us Tri-Glycerides versus Mono- or Di- Glycerides. It’s simply telling you how many acid chains are present. Each acid chain within a fatty acid compound might be the same acid... or it might not.

Each type of acid chain present lends a different quality to the finished soap. It can take years of study – or simply a single-mindedness about doing so – to find out which acid chain lends what qualities, and which fats they’re generally available in. Fortunately, you do not have to know which acid is in which fat at what proportions in order to get a good soap! There are a lot of sources already out there in the world which will tell you what fats are going to be most helpful.

Balancing the Recipe

Just like any other chemical formula, a soap formula has to be balanced in order to work right, and not have undesirable elements left over after the reaction finishes taking place. The way to balance a soap formula is to know which oils (fats) you’re going to use, and what their SAP values are. The SAP value of a fat is its Saponification Value – that point where it turns properly into soap, with no lye left over to cause a problem.

There are several programs available online which are used by modern Soapers – SAP calculators like SoapMaker are probably the most commonly used. It’s a great little program, and in any situation short of TEOTWAWKI, comes in very handy for those who don’t want to have to deal with working out the calculations. There are also places where you can find rather detailed lists of commonly-used fats and their respective SAP values, along with the actual mathematical equation needed to make a balanced soap recipe.

One of the reasons that I like – and still use – SoapMaker as a program is that it will automatically make all of your recipe adjustments for you based on various criteria ranging from the size of your mold, what percentage of a specific oil you want to use, to how strong you desire your lye solution to be. It will even graph out for you what several commonly looked-for qualities in your finished soap are going to be like, including hardness (how durable the soap is going to be when left in water) and moisturizing ability (how well it will lather, and how stable or fluffy that lather will be)

The most commonly-used fat in soap making has traditionally been olive oil. It was used by the ancient Greeks, Romans, and Egyptians, and there is evidence that it was in use as a soap making oil by the Etruscans and Phoenicians as well. Olive oil, when used by itself – traditionally called Castille soap (named for the Castille region of Spain) – is very moisturizing, and very easy on even sensitive skin, but the lather isn't very stable at the best of times, and it tends to dissolve rapidly if it’s not placed where it will drain completely and dry out between uses.

Olive oil, along with lard (melted, cleaned fat from pigs and wild boar) and tallow (fat from cows, goats, sheep, and various types of deer or buffalo) has been in use the longest. Lard and tallow both make for soaps that are very hard bars which survive well even when left in water, but they don’t always cooperate in making a good lather in cold or hard water.

Coconut oil has been in use in some areas for as long as it’s been pressed, much like olive oil in the Mediterranean region. Coconut oil makes a much harder bar than olive oil by itself, with a much more stable lather, but like lard and tallow it tends to have a drying effect on many skin types.

A great compromise these days is vegetable shortening – Crisco and its generic store brand offspring – which is made from hydrogenated soybean, cotton seed, and corn oils. It’s extremely shelf stable, cheap and easy to acquire, and tends to produce a soap that is hard enough to last a while, without being excessively drying, and with a decent lather even in cool water.

Next Installment

I’ll go over the actual process of creating soap from the raw ingredients of fats, water, and lye. I’ll also provide a couple of tested recipes, along with conversion rates to list the recipe in ounces, grams, and cups for ease of use.