If you’ve ever ventured into the world of cold process soap making, you’ve probably encountered the term saponification. It’s the chemical reaction that occurs when oils or fats combine with lye (sodium hydroxide), resulting in soap. While this process might sound a little complex, understanding how to calculate the right amount of lye is crucial to ensuring your soap turns out perfect every time.
Getting the lye measurement wrong—whether too much or too little—can impact the soap’s texture, lather, and overall quality. But don’t worry, we’re here to make the process simple. In this guide, we’ll break down the science behind saponification and show you exactly how to calculate lye for cold process soap in a straightforward, easy-to-understand way.
What is Saponification?
Before diving into how to calculate lye, let’s first understand the process of saponification.
Saponification is the reaction that occurs when a fatty acid (from oils) and an alkali (lye) react together to form soap and glycerin. In other words, oils or fats are converted into soap with the help of lye.
Here’s the basic equation for saponification:
Fat (oil) + Lye → Soap + Glycerin
The key to making great soap is ensuring the correct balance between oils and lye. Too much lye, and the soap could become harsh and irritating. Too little, and the soap might not fully form, leaving behind excess oils.
How Much Lye Should You Use for Cold Process Soap?
The amount of lye you need depends on several factors, including:
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Type of oil you are using (different oils require different amounts of lye)
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Weight of oils in your recipe
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Superfat percentage (more on that below)
Lye calculation isn’t something you should guess; it needs to be accurate for safety and effectiveness. Fortunately, there are a few easy methods for determining the correct amount of lye.
Superfatting and Why It’s Important
Before we get into the calculations, let’s quickly talk about superfatting.
Superfatting is the practice of adding extra oils to your recipe that don’t go through saponification. This gives your soap extra moisturizing properties and ensures that no lye is left unreacted in the final soap.
For example, if you have a superfat of 5%, that means 5% of the oils in your recipe will not be converted into soap. Superfatting is important because it helps balance the harshness of the lye and ensures your soap is gentle on the skin.
When you calculate lye, you’ll need to account for the superfatting percentage to avoid using too much lye.
How to Calculate Lye for Cold Process Soap: The Easy Way
There are two main methods to calculate the right amount of lye: using an online lye calculator or doing the math manually with a saponification chart. Here’s how to do both!
1. Using a Lye Calculator
The easiest and safest way to calculate lye for your cold process soap is by using a lye calculator. These online tools automate the math and ensure that your measurements are precise.
Here’s how to use a lye calculator step by step:
Step 1: Choose a Reliable Lye Calculator
There are many lye calculators available online. Some popular and trusted ones include:
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SoapCalc (soapcalc.net)
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The Sage Lye Calculator (thesage.com)
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Bramble Berry Lye Calculator (brambleberry.com)
All of these calculators are easy to use and designed for beginners, but SoapCalc is one of the most commonly used tools in the soap-making community.
Step 2: Enter Your Recipe Information
Once you’ve chosen your calculator, you’ll need to enter the oils and fats used in your recipe. For each oil, you’ll enter the weight (in ounces or grams) and select the oil type from a list of options.
For example:
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Olive oil (100g)
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Coconut oil (50g)
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Castor oil (30g)
Most calculators have preset options for popular oils, so you don’t need to manually find their saponification values.
Step 3: Select the Superfat Percentage
Choose your preferred superfat percentage. Most soap makers go for a superfat of around 5%, which means 5% of the oils in your recipe won’t turn into soap.
This step is important because it adjusts the amount of lye to ensure that excess oils remain in your soap.
Step 4: Calculate the Lye
Once you’ve entered all the required information, hit the “calculate” button. The calculator will generate the exact amount of lye (sodium hydroxide) needed for your recipe. It will also give you the amount of water to use in your lye solution.
For example, if your recipe includes 180g of oils, the calculator might tell you that you need 68g of sodium hydroxide and 120g of water.
Step 5: Double-Check Your Results
It’s always a good idea to double-check your results and ensure the numbers look correct. You should always be cautious when working with lye and ensure you’re following the recipe precisely.
2. Manual Lye Calculation with a Saponification Chart
If you prefer doing the math yourself, you can manually calculate the lye using a saponification chart. A saponification chart lists the “SAP value” for each oil, which is the amount of lye required to turn a certain weight of oil into soap. The process involves a few more calculations, but it’s not too difficult once you get the hang of it.
Step 1: Find the SAP Value for Each Oil
Each oil has a specific SAP value, which tells you how much lye (in grams) is required to saponify 1 gram of that oil. You can find these values in a saponification value chart for different oils, which is available online or in many soap-making books.
Here are some example SAP values:
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Olive oil: 0.134
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Coconut oil: 0.190
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Palm oil: 0.141
Step 2: Multiply the Oil Weight by the SAP Value
Next, you multiply the weight of each oil by its respective SAP value to determine the amount of lye needed.
For example:
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Olive oil: 100g x 0.134 = 13.4g of lye
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Coconut oil: 50g x 0.190 = 9.5g of lye
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Castor oil: 30g x 0.128 = 3.84g of lye
Step 3: Total the Lye Amount
Once you have the lye amounts for each oil, add them up to get the total amount of lye required for the recipe.
For our example:
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13.4g (olive oil) + 9.5g (coconut oil) + 3.84g (castor oil) = 26.74g of lye
Step 4: Adjust for Superfatting
If you want to superfat your soap (which we recommend for beginners), you can adjust the amount of lye used. To calculate this:
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Multiply the total amount of lye by your superfat percentage (e.g., 5%).
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Subtract that from the original total lye amount.
For example, if you want a 5% superfat:
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5% of 26.74g = 1.34g
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26.74g – 1.34g = 25.4g of lye
So, for a superfat of 5%, you would need 25.4g of lye.
Safety Considerations When Working with Lye
Handling lye safely is essential when making cold process soap. Here are a few safety tips:
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Wear protective gear: Always wear gloves, goggles, and long sleeves when handling lye.
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Work in a well-ventilated area: Lye can create fumes when it reacts with water, so ensure proper ventilation.
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Always add lye to water: Never pour water into lye, as it can cause a violent reaction.
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Store lye safely: Keep lye in a sealed, labeled container out of reach of children and pets.
Conclusion
Calculating the right amount of lye for cold process soap might seem tricky at first, but with the help of lye calculators or a little math, it’s a manageable process that becomes second nature as you gain more experience.
Whether you choose to use an online calculator or manually calculate your lye, always remember to double-check your measurements and use safety precautions. With this knowledge, you’ll be able to craft beautiful, high-quality soap that’s perfectly balanced and gentle on the skin. Happy soap making!