Handmade Liquid Castile Soap Recipe
Handmade liquid castile soap with just olive oil, potassium hydroxide, water, and vegetable glycerin is the gentlest, most versatile liquid soap you can make. There is also an option to make this without glycerin, right below the original recipe.
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This post also contains a video demonstrating how to make the liquid castile soap.
This post also includes a video, in which I made a double batch, so it will look like a lot! This is a great beginner-friendly introduction to liquid soapmaking
This liquid soap is perfect for:
- baby wash
- hand soap
- body wash
- household cleaner
- even pet shampoo
Homemade Liquid Castile Soap (Olive Oil)
Oils
| Ingredient | Weight |
|---|---|
| Olive oil (virgin or extra virgin is fine) | 17.5 oz (500 g) |
Lye Solution (for liquid soap)
Liquid soap uses Potassium Hydroxide (KOH), not NaOH.
| Ingredient | Ounces | Grams |
|---|---|---|
| Distilled water | 9.5oz | 268 g |
| Vegetable glycerin | 4 oz | 114 g |
| KOH (90%) | 4.5 oz | 132 g |
This is calculated for 3% superfat.
Optional: Making without Glycerin
| Ingredient | Weight |
|---|---|
| Potassium hydroxide (KOH, 90% purity) | 4.5 oz (132g) |
| Distilled water | 13.5 oz (382 g) |
Step 1 — Make the Paste (Hot Process)
- Heat olive oil in a slow cooker on low.
- Carefully add KOH to water (never reverse). Stir until dissolved.
- Pour lye water into warm oil.
- Slowly and gently add the glycerin
- Stick blend until thick trace (like pudding).
- Cover and cook on low. You can check on it and stir from time to time.
- Watch the heat, don’t allow it to get above 185 degrees F. This will cause it to be foamy. If you keep your crockpot on low or keep warm you should be fine. If the temperature gets too high, it’s not the end of your soap, just turn it down.
You’ll see stages:
- applesauce
- mashed potatoes
- glossy taffy
- thick translucent gel
This takes 1–2 hours.
Step 2 — Test for Doneness
Dissolve a small piece of paste in hot water.
If it’s clear, the paste is done.
If cloudy, cook 30 minutes more.
Step 3 — Dilute the Paste
Use this dilution ratio:
This is a 2.5: 1 water to paste ratio. I like to just add all the water to the crockpot and let it dissolve on low for several hours or overnight. For this recipe, start with 2.5 quarts distilled water. This yielded a very nice thick soap once it was all dissolved.
The way to know if you have enough water is to check for a film on top. If there is a thick film after fully dissolving, you could add more water.
** Another option is to store it and wait to dilute the paste. It can be stored in a clean jar and diluted as you need. Add about 2.5 oz of water to 1 oz of paste.
Step 4 — Optional Additions (after dilution)
Per 16 oz diluted soap:
- 0.2–0.3 oz essential oils (optional)
Why is this true Castile?
- 100% olive oil
- Extremely gentle, low cleansing
- Safe for sensitive and baby skin
- Historically accurate Castile formula
Uses
Dilute further depending on use:
| Use | Dilution |
|---|---|
| Hand soap | Use as is |
| Body wash | Use as is |
| Baby wash | 1 part soap : 1 part water |
| Foaming pump | 1 part soap : 3 parts water |
| Household cleaner | 1 part soap : 4 parts water |
Cure Time?
None! Liquid soap is ready as soon as diluted.
