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 can change how fast the alkali can attack the fat molecules. For most typical soap recipes, more water tends to slow saponfication and less water tends to speed up saponification. Although there exceptions to this general pattern, this rule of thumb often holds true for typical soap recipes:
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.
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 other liquid oils with large amounts of unsaturated fatty acids. Soap that is rich in these fats 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.
Unfortunately, the math involved with the "water as % of oils" setting does exactly the opposite -- it calls for more water to be used with recipes that need less and vice versa.
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. Soap recipe calculators....
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
"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 any blend of fats. Until recently, all of the soap recipe calculators on the internet 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 Exercise 1 (above), 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 water:lye ratio 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 soap recipes and that gets beginning soap makers in trouble. I give the reasons why in this table....
Less common definitions of "full water" discussed by respected soap makers include a 1:1 water:lye ratio (50% lye concentration) (2) and a 3:1 water:lye ratio (25% lye concentration) (3).
Kevin Dunn, author of Scientific Soapmaking, surveyed recipes in soap-making books published from the 1970s through the 2000s. Water:lye ratios in these recipes varied widely from 3.0 to 1.16 (lye concentrations from 25% to 37%). (1)
This information shows soap making authors obviously do not agree there is one "best" proportion of water to lye for making soap and there is no single, widely-accepted definition for "full water."
But won't more water in the lye solution be safer?
Some people believe the lye solution used for "full water" soaping is less dangerous because the alkali is supposedly diluted in more water.
It is true that dilute lye solutions (solutions with less than 10% lye concentration) are somewhat safer to handle than more concentrated solutions, but soap makers do not use weak lye solutions like this. We use lye solutions that range from 3:1 to 1:1 water:lye ratio (25% to 50% lye concentration).
An NaOH or KOH solution at 3:1 water:lye ratio (25% lye concentration) is not any less risky than a solution at a 1:1 water:lye ratio (50% lye concentration). When a lye solution is anywhere within this concentration range, severe injury can happen within mere seconds. Be sure to use the same method of handling these lye solutions; wear the same kinds of eye, respiratory, and hand protection; and follow the same first aid treatment.
Water Discount
"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 there is no generally accepted basis for "full water."
The "water discount" percentage is meaningless unless you also know the basis used to define "full water" and the method used for calculating the water discount.
Better ways to calculate water: lye concentration and water:lye ratio
When soapers ask for help, 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 "water:lye ratio" and the other is "lye concentration."
The numbers forwater:lye ratio and lye concentration may look different, but they mean exactly 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 of my background in the chemical industry, it makes more sense to me to use lye concentration. Other sciency types might feel the same. 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 with tips for choosing an appropriate lye concentration or water:lye ratio, if you need some suggestions to get started. It also shows how to calculate water:lye ratio and lye concentration as well as how to convert from one to the other.
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 and other essential oils, 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
Intensity of mixing: Stick blending or vigorous hand whisking tend to accelerate trace and saponification. Hand stirring with a spoon or spatula slows things down.
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.
In summary
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!
References
(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/
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