Soaping, like many crafts and professions, has its own lingo and traditions. Have you heard that beginners should only make "full water" soap and a "water discount" should only be used by the experts? Have you wondered what "water as % of oils" really means?
All three phrases relate to the amount of water used when making soap, but they are concepts that interfere with the goal of consistently making good soap. I want to explore these ideas and suggest better ways to choose the amount of water for more reliable soaping results.
Water as % of Oils
"Water as % of oils" is a method of calculating the amount of water based on the weight of fats in the recipe.
Most soap recipe calculators are set to a default of "38% water as % of oils." This means a soap recipe will have 38 grams (or 38 ounces) of water for every 100 grams (or 100 ounces) of fats.
The problem with using "water as % of oils" is that the amount of water in proportion to the fats is not particularly important. What is more important to the chemistry of saponification is the amount of water in proportion to the alkali (NaOH or KOH).
Water modifies how fast the alkali can attack the fat molecules.
If you want to slow the rate of saponification, use more water in proportion to the alkali. This is helpful for soap that has a lot of coconut, palm kernel, or babassu oil. Without enough water, soap with these fats is notorious for overheating and cracking and sometimes even overflowing the mold like lava from a volcano.
If you want to speed up the rate of saponification, use less water in proportion to the alkali. This is helpful for soap that has a lot of olive oil and similar liquid oils. With too much water, this type of soap can take forever to come to trace, the soap sometimes separates in the mold, and it can take ages to harden up before the soap can be removed from the mold.
Exercise 1: See how "water as % of oils" works
Open your favorite soap recipe calculator. And if you have not yet learned to use a soap calculator, now is the time to start. Of all the online calculators available, I recommend Soapee.com or SoapmakingFriend.com if you are fluent in English. These are full featured calcs that are easy to use.
Set up two simple soap recipes with just water, NaOH, and fat. One will use 100 grams (or ounces) of 100% coconut oil. The other one will use 100 grams (or ounces) of 100% olive oil. Use the default setting of "38% water as % of oils" for both. Leave the superfat at the default -- usually 5%.
Look for the total water weight in each recipe. You will see the two recipes call for the exact same grams (or ounces) of water -- it should be 38 grams (or ounces) for both.
Look for the "water:lye ratio" for both recipes. Compare these two numbers. Are they the same? If not, which recipe has the larger water:lye ratio?
As the number for the "water:lye ratio" gets bigger, that means there are more grams of water in the recipe for every gram of NaOH.
A water:lye ratio of 2 means 2 grams (or ounces) of water for every 1 gram (or 1 ounce) of NaOH.
A water:lye ratio of 3 means more water -- 3 grams (or ounces) of water for every 1 gram (or 1 ounce) of NaOH.
Which recipe has more water in proportion to the alkali (NaOH)? (Hint: It is the recipe with the higher water:lye ratio.)
Is this recipe the one that would benefit from more water to slow down saponification? (Hint: No, it's not!)
"Full water" is the idea that there is a particular water content that is a standardized "benchmark" amount for making cold process (CP) soap. Unfortunately there is no consistent definition of what this "full water" benchmark really is.
Definition 1. One common definition of "full water" is the water weight that results if "38% water as % of oils" setting to calculate the water for for any blend of fats. All of the soap recipe calculators I have looked at and many books, tutorials, videos, and online forums use this "38% water as % of oils" as the norm, and many soap makers use this default setting for every recipe they make.
If you did the exercise I suggested earlier, you will know the results from "38% water as % of oils" range from a 3:1 water:lye ratio (25% lye concentration) for a 100% olive oil soap to 2.23 water:lye ratio (31% lye concentration) for a 100% coconut oil soap. This rule creates a lot of variation in the water-to-alkali content from recipe to recipe.
Definition 2. A second definition of "full water" is the lye concentration that results if "38% water as % of oils" is used to calculate the water for a classic "trinity" soap blend of 1/3 coconut oil, 1/3 olive oil, and 1/3 palm or lard. In this definition, the amount of water in proportion to alkali is about 2.57 water:lye ratio (28% lye concentration). This consistency is an improvement over Definition 1, but the downside is that a 2.57 water:lye ratio is too much water for many recipes. I explain more in this table....
Less common definitions of "full water" discussed by respected soap makers include 50% lye concentration (2) and 25% lye concentration (3). Kevin Dunn, author of Scientific Soapmaking, surveyed recipes in soap-making books published from the 1970s through the 2000s. Lye concentrations in these recipes varied widely from 25% to 37% (water:lye ratios from 3 to 1.16).(1)
But isn't "full water" safer?
Some people believe the lye solution used for "full water" soaping is less dangerous because the alkali is diluted in more water. That is true for lye solutions under 10% concentration, but soap makers use lye solutions that are much more concentrated than this.
An NaOH or KOH solution at 25% concentration is not any less risky than lye solution at a 50% concentration. Use the same method of handling these solutions; wear the same kinds of eye, respiratory, and hand protection; and follow the same first aid treatment.
"Water discount" is the practice of using less water to make soap than the "full water" amount. You will hear soapers say, "I did a water discount of 10% for my last batch" or something like that. But if you do not know the "full water" basis from which the "water discount" is taken, this information is meaningless.
Better ways to calculate water -- lye concentration and water:lye ratio
When soapers ask for help at the Soap Making Forum, common complaints include the soap staying too soft for days after saponification, separating in the mold, weeping liquid, showing unsightly "glycerin rivers", overheating, cracking, and so on. Many are using "38% water as % of oils" to calculate their recipes, and this is one reason why these problems happen. These soapers would have fewer troubles if they would calculate the the water content based on the alkali weight.
There are two common ways to calculate water based on alkali. One is "lye concentration" and the other is "water:lye ratio."
The numbers for lye concentration and water:lye ratio may look different, but they mean the same thing mathematically. Pick the one that makes the most sense to you and stick with it.
Many soapers prefer water:lye ratio because it is more intuitive to non-chemist types. Higher water:lye ratio => More water
Because I am a chemical engineer and I once worked as technician in a chemistry lab, lye concentration makes more sense to me. Higher lye concentration => Less water
Remember -- Water:Lye Ratio and Lye Concentration mean exactly the same thing; they just look different. They are NOT mathematically the same as "Water as % of oils." You cannot easily translate a "Water as % of oils" percentage to either of the other two.
Here is a table that connects lye concentration and water:lye ratio. The table also provides tips for choosing an appropriate lye concentration or water:lye ratio if you need some suggestions to get started.
As you gain more experience, you will develop your own preferences. Issues that may affect your choice of lye concentration include --
Food ingredients that cause soap to heat up -- Sugars (table sugar, honey, maple syrup, etc.), beer, food purees, etc.
Chemical accelerants -- Eugenol, a chemical found in clove essential oil, and some fragrances (many florals in particular)
Design plans -- Complicated swirls needing more working time versus simple swirls or uncolored soap that is faster to make
Temperature of ingredients -- Warmer ingredients tend to accelerate saponification
Exercise 2: See how lye concentration affects your soap making
If you are new to making soap, you might want to experiment a bit to see what lye concentration settings (or water:lye ratios) work best for you. Keep in mind that small changes in the water will make definite differences in your soap, so don't go crazy.
Using your favorite blend of soaping fats, calculate a recipe using 28% lye concentration (2.57 water:lye ratio), and make a batch of soap. See how the process goes and how the soap turns out.
Make a second identical batch except use 30% lye concentration (2.33 water:lye).
Make a third batch using 33% lye concentration (2.03 water:lye).
Evaluate the soap from the three batches. Some questions you might want to answer include --
Which recipe behaved best when you made the soap?
Did one recipe come to trace a lot faster or slower than the others?
Did the molded soap stay overly soft or was it firm fairly quickly?
Is there a difference in the appearance of the soap from the various batches?
Doesn't changing the lye concentration change the weight of the lye?
The alkali (lye) weight does not change if you change the "water as % of oils" setting, lye concentration, or water:lye ratio. These settings only change the amount of water in the recipe.
The alkali weight is determined by the kinds of fats in your recipe, the weight of those fats, and the superfat (lye discount) setting you choose. If those three things stay the same, the alkali weight stays the same too, no matter what you do to the settings for lye concentration or water:lye ratio or "water as % of oils".
Exercise 2 (above) asks you to create three soap recipes that are identical except for different lye concentrations (or water:lye ratios). If you compare these recipes, you will see the alkali weight for the recipes stays the same; only the water weight changes.
An analogy -- Mix 1 cup (250 milliliters) of sugar in 2 quarts (2 liters) of water, as if making a pitcher of Kool-Aid sweetened drink. This sugar-water mixture is going to be pleasantly sweet to drink. Next, mix 1 cup (250 mL) of sugar in just 1 pint (0.5 L) of water -- the SAME amount of sugar, but a lot less water. This mixture is going to taste much sweeter because the sugar is concentrated in less water.
In this analogy, the same amount of sugar is used with different amounts of water. Changing the lye concentration or water:lye ratio does the same thing -- the alkali (lye) stays the same; only the water changes.
If you start using lye concentration or water:lye ratio, you will learn that tweaking the water content a little higher or a little lower is just a normal adjustment to make, not something to be scared of.
Find the range of lye concentrations (or water:lye ratios) that works best for your personal soaping style and the kinds of soap you make. Enjoy your soaping!
Extra Credit. When did 38% water as % of oils become a "thing"?
I have been trying to find when "full water" was first defined as "38% water as % of oils" without much luck. Booklets and pamphlets for making homemade soap dating to the early to mid 1900s do not explain how to calculate soap recipes. They just provide pre-made recipes.
I suppose someone in recent decades analyzed these older recipes and came up with the water-based-on-fat method and also decided to standardize on the "38% water as % of fats" default.
The water-based-on-fat method would have been an easy rule to use when programming the first soap recipe calculators, so my guess is this method may have originated with the earliest of the online recipe calcs.
I believe online soap recipe calculators first became available in the early 2000s. In her 1997 book "The Soapmaker's Companion", Susan Miller Cavitch lists soap making forums and discussion groups on the internet, but she makes no mention of any online calcs.
I checked the Wayback Machine for information about the age of Summerbeemeadow and SoapCalc, the oldest online calcs I know of.
The archves show the basic Summerbeemeadow (SBM) calc went live in mid 2002. The advanced SBM calc was added in early 2010. That basic version of the SBM calc was (and still is) very simple with no way to alter the water content.
I cannot tell if the early versions of the SBM calc used the "38% water as % of fats" rule, because websites archived on the Wayback Machine cannot do calculations and queries. The current-day basic and advanced SBM calcs still do not allow the water content to be altered by the user, but it appears they calculate the water content based on a 30% lye concentration.
The popular SoapCalc was first archived on the Wayback Machine in 2009, so I presume this is when SoapCalc first became available on the internet. Even in its early incarnation, SoapCalc allowed the user to adjust the lye concentration and water:lye ratio, but the default for water content was the water-based-on-fat default of "38% water as % of oils."
The use of alkali weight to determine the water weight is not a new concept. Many handcrafted-soap makers have been using the water-based-on-alkali method for at least as long as other soap makers have used the water-based-on-fat method.
In 1995, Susan Miller Cavitch published The Natural Soap Book: Making herbal and vegetable-based soaps. She does not clearly explain how to calculate the amount of water in this book, but she does say the water content should be based on the amount of alkali --
"...Too little water won't bring the [sodium hydroxide] into solution, causing the final soaps to be brittle and dry. Too much water will add unnecessary moisture to the soaps, making them less lasting and too soft. ... Keep in mind that a formula is somewhat flexible with respect to the amount of water required to dissolve an amount of sodium hydroxide; acceptable amounts need not be exact, but rather fall within a range...." (4)
Elizabeth Letcavage and Patsy Buck originally published Basic Soapmaking in 2009. Like Cavitch, they advised soap makers to base the water weight on the alkali weight --
"...multiply the weight of the lye by 2.5 to get the weight of water to be used. This is the mathematical formula: Lye x 2.5 = H2O. ... The 2.5 value is somewhat flexible, however. You may choose to use more or less, but remember that you must have enough water to dissolve the lye. Do not go below a multiplication factor of 2.0..." (5)
The water:lye ratio of 2.5 is the same as a lye concentration of about 28%. The water:lye ratio of 2.0 is a lye concentration of about 33%.
Discussions on this topic since the beginning clearly show the water-based-on-fat method was often used by soapmakers to determine the water content in their recipes. Many of these soapmakers are as skeptical as I am about the usefulness of "full water" and "water discount" --
A comment in a 2008 thread-- "...Most soapers consider a 33% lye solution a discount...."
A comment from a 2009 thread -- "...I like talking in terms of lye solutions over the term 'water discount' because water discounts are quite a hazy, inconsistent animal in comparison to lye solutions for me...."
A second poster in this same thread explained, "...saying something like "I use a 34% water discount" could be interpreted several different ways...."
A comment from another 2009 thread -- "...I recommended to ... that she try not using the default - Water as a % of Oils - on SoapCalc, but rather try a batch using a Lye Concentration of 33%...."
And here is a gem from a third 2009 thread -- "...'Full water' is a nonsense term - it simply means using the default amount of water recommended by the calculator, and different calculators recommend different amounts. 'Discount' is the other nonsense term - because it means discounting (as in reducing) the amount of water, and the % discount is impossible to know unless you know the starting point, but since different calculators have different default amounts..."
(1) Dunn, K., Scientific Soapmaking. Clavicula Press, 2010, pg 293-294
(2) Lindberg, Clara. Lye calculation using a saponification chart -- Tutorial. See the section headed "What about the water?" Auntie Clara's Handcrafted Cosmetics. https://auntieclaras.com/2018/09/lye-calculation-tutorial/
(3) Kenna. How to better understand water discounts when you make soap. See the section headed "The Most Common Lye Solution Strengths in Soapmaking." Modern Soapmaking. https://www.modernsoapmaking.com/lye-solution-in-soapmaking/
(4) Cavitch S M, The Natural Soap Book, 1995, Chapter 3: Lye and Water.
(5) Letcavage E and Buck P, Basic Soapmaking, 2009, Chapter 5: Creating your own soap recipes.
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