How to Rebatch a Lye Heavy Soap
This post includes basic instructions for re-batching lye heavy cold processed soap. It happens to the best of us sometimes!
What does it mean to say a batch of soap is ‘lye heavy’? Excess lye occurs in handmade cold processed soap when too much sodium hydroxide (lye) or not enough oil are used in the soap batter mixture. This can result from a mistake in measuring or calculating the soap recipe ingredients, or a poorly formulated recipe. Soap that is too alkaline (pH too high) needs correcting before it can be safely used.
Here is the video I made demonstrating the process I follow to correct lye heavy soap. Below that is a written summary of the process.
How to fix a lye heavy soap?
Step 1: Identify if your soap is lye heavy
Sometimes we know exactly what we’ve done wrong with a lye heavy soap, but sometimes we don’t! The first step is to test your soap with pH test strips, or use the old fashioned zap test to identify if your soap is lye heavy or not. Your soap will be lye heavy if it was made with either too much sodium hydroxide, too little oil, or the oils/fats used were incorrect for the amount of sodium hydroxide used.
Step 2: Grate the soap
Grate or slice the soap into small pieces. The smaller and finer the pieces, the better! Once grated or cut, add your soap to a large stainless steel pot or slow cooker/crock pot.
Step 4: Cook the soap with extra water and fat/oil
Add a small amount of water to your grated soap and turn the heat to medium -low. Water will help to steam the soap, encouraging it to melt. Use very low heat and monitor closely if using a gas stove.
You will also need to add some additional oil or fat to your grated soap, to correct the excess lye. Which oil you use, and how much you will need, is up to you - this depends on the original recipe, what oils were used and what type of extra oil, butter or fat might benefit the recipe.
Sometimes our soap is lye heavy because we accidentally left out one of the oils or fats when making it the first time. If this is the case and you know which oil was left out, you can simply add that to the rebatch pot to correct your soap recipe.
Step 5: Cook and test the soap
Stir and cook the soap thoroughly each time after adding new oil to the pot. This is essential if you aren’t sure how much oil is required to correct the soap. Newly added oil requires heat and thorough mixing with the melted soap to force saponification and ensure the excess lye is consumed. Use a stick blender to assist thorough mixing of the soap.
Special note: I highly recommend rebatching lye heavy soap in small quantities - I commented in the video about how difficult and slow it was to stir and completely cook through my very large batch of rosemary soap!
Step 6: Repeat until the soap has the correct pH
Continue stirring, cooking and testing the soap, adding more oil if needed, until the soap tests in the correct pH range. Your soap should be around 8-9 pH when fully saponified.
Step 7: Add any additional ingredients
Add more colour or fragrance to your soap if desired. Make sure you follow supplier guidelines and recommended usage rates, and take into consideration previous amounts used in the batch, when adding fragrance oils or essential oils. I added more essential oil to my large rosemary soap rebatch at a rate of 2% essential oil of the entire soap weight. This was appropriate because I used a very minimal amount of essential oil in the soap when I first made it, and only half the original batch was scented.
Step 8: Mould the soap
When you are satisfied with your rebatch, spoon the soap into moulds to cool and harden before cutting. The rebatched soap may need to sit for a few days to become firm enough to cut, depending on how much water was added. Once cool and firm enough, cut the soap into bars and place on a rack to dry.
Step 9: Re-dry/cure the soap
Due to the water added during the rebatch process, it is most likely that your soap will benefit from 1-2 months drying time before it can be used. As long as the pH is correct (which it now should be!), you can test the lather of your soap after a couple of days, however it will be at its best once fully dried and hardened.
Congratulations, you fixed your soap!
I hope you enjoyed this video and written resource. Please let me know if you have any questions, you can ask them below, or in the comments section on YouTube.
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