Soapy Math Part 1: How to Calculate Your Lye

Why bother doing soapy math by hand when we have the use of lye calculators to do the calculating for us? Well, because that lye calculator will only get you so far! There are a variety of math calculations you need to understand to formulate, create, and troubleshot recipes.

#soapymath #calculatingarecipe #coldprocesssoap #calculatingyourlye

I've divided this lecture into a four part series. The next three parts will go live on the next three Saturdays. So, be sure to check back for those videos. The goal of these videos is to teach you how to calculate a recipe from scratch and in turn help you understand what each element of a lye calculator does. So, let's get started!

HANDOUT Available for purchase: https://jennifersoap.com/collections/...

PART 1: CALCULATING YOUR LYE

Using a SAP Chart or Spec Sheets from the supplier you will determine the SAP value for each oil you need for your recipe. The SAP charts tell you the number of milligrams of sodium hydroxide (lye) required to completely saponify one gram of a specific fat is referred to as the saponification value or SAP value. When you look at SAP values on charts there will be two different values typically. One for potassium hydroxide (used in liquid and cream soap making) and one for sodium hydroxide (used for making bar soaps).

Let’s look at an example:

If you want to determine what the SAP value is for avocado oil then you’d look up avocado on the chart:

Fat or Oil NaOH KOH
------------------------------------------------------
Almond Oil 0.1367 0.1925
Apricot Kernel Oil 0.1378 0.1941
Avocado Oil 0.1337 0.1883

SAP Chart by Certified Lye: http://www.certified-lye.com/lye-soap...

In this case we look under Sodium Hydroxide. So, your SAP value is 0.1337.

Measuring: By Weights, Not by Volume
It’s important to ALWAYS measure by weights (pounds, ounces, grams) and NEVER by volume (cups, teaspoons, tablespoons). Always use the same unit of measurement for all your ingredients. If you weigh your oils in ounces you must weigh your lye in ounces.

For example:
Apricot Kernel Oil has a saponification value of: 0.1378
This means it will require 0.1378 ounces of lye to saponify one ounce of apricot oil. If you were measuring in grams then it would require 0.1378 grams of lye to saponify one gram of apricot oil.

Determining Lye Amounts
To determine the amount of lye you need to saponify each oil in your recipe you must find the SAP value for each oil. Then you multiply the amount of fat by the SAP value to determine the amount of lye needed to saponify that oil.

(Amount of Fat) x (SAP Value) = (Amount of Lye)
Example: One Oil Recipe 32 oz Avocado Oil
32 oz x 0.1337 = 4.28 oz

Example: Multiple Oil Recipe
12 oz Olive Oil
6 oz Coconut Oil
6 oz Palm Oil
2 oz Shea Butter

Step 1
Determine the amount of lye needed to saponify each oil.

Olive Oil: 12 oz x 0.1353 = 1.62 oz
Coconut Oil: 6 oz x 0.1910 = 1.15 oz
Palm Oil: 6 oz x 0.1420 = 0.85 oz
Shea Butter: 2 oz x 0.1296 = 0.26 oz

Step 2
Add up the total amount of lye needed for each oil

1.62 + 1.15 + 0.85 + 0.26 = 3.88 oz

The total amount of lye needed to saponify the oils in this recipe is: 3.88 oz

Converting KOH to NaOH (and vice versa)
Saponification tables generally give you the NaOH and KOH SAP value. However, most specification sheets give the SAP Value for KOH and you’ll have to convert it to NaOH. This is a simple step. You simply need to divide (convert KOH to NaOH) or multiply (convert NaOH to KOH) by 1.403 (this is the molecular weight of sodium hydroxide).

----------------------------------------------------------------------

Soap Embeds: Love embeds, but don't have the time or patience to make your own? Check out my Soap Embeds for Soap Makers: https://jennifersoap.com/collections/... I make a variety of embeds that I sell on my webpage. You get gorgeous embeds, but don't have to worry about making them!

Soap Extruder Discs: Looking for new and fun extruder discs shapes? Check out my (ever growing) collection here: https://jennifersoap.com/collections/...

Jennifer's Handmade Soap - Because soap should be more than just functional!
Webpage: www.jennifersoap.com
Facebook: www.facebook.com/JeniferSoap
Instagram:   / jennifer_soap  
TikTok:   / jennifersoap