Instructions for making a natural Castile soap recipe with the simplest of ingredients. Also includes tips on how to harden it up and cure olive oil soap faster.
So many soap recipes call for four or more oils, lots of additives, and enough essential oil to bankrupt you. Fortunately, making pure and natural handmade soap can be as simple as just three readily available ingredients.
Olive oil soap, or Castile soap, is one of the most traditional types you can make. However, if you’ve made cold-process soap before you might be a little alarmed by the time that some of the steps take. Don’t worry though, I’m here to guide you through making some of the most skin loving soap you’ll ever use.
Soap Making Oils
Technically you can use any oil to make soap but each one has a different soap making property. Coconut creates hard bars with fluffy lather, Sunflower oil creates softer, conditioning bars, and Castor oil creates big fluffy lather. There are few single oils that make a really good batch of soap though and that’s why so many recipes call for a mixture of lots of different ones. Too much coconut oil and your bars might be drying, too much castor oil and they might be sticky.
Two of the exceptions to this are tallow soap and pure olive oil soap. In the case of olive oil soap, you can use extra virgin olive oil or Pomace olive oil to make it. The former will be more expensive but will be a higher quality and more natural product. You can read more about what Pomace olive oil is and how it’s extracted here.
About Castile Soap
On its own, olive oil can make a good hard bar that’s sensitive, nourishing, and doesn’t over-dry your skin. It has quite a unique lather though that I’ll call creamy but you’ll hear others call slimy. It lacks the big fluffy bubbles that coconut oil or castor oil can give but in all honesty, I love it. No other soap feels quite as gentle as a bar made out of extra virgin olive oil.
It’s not entirely clear when soap was invented but some of the earliest we know of was made of olive oil and laurel oil. Called Aleppo soap, these bars were introduced (or re-introduced) to Europe after the Crusades. Laurel oil wasn’t readily accessible so soap makers in the Castile region of Spain started making soap without it. Hence, the invention of pure olive oil soap.
Making olive oil soap
I mentioned before that making olive oil soap could be a bit alarming for soap makers. That’s because it takes longer for it to come to ‘Trace’, longer for it to harden in the mould, and longer for it to cure. If you prepare yourself for that, then making it is easy.
There are a couple of steps that I’ve woven into this recipe that should help with this time issue. We’ll be using less water than in typical soap making recipes and the optional ingredient Sodium lactate helps to harden bars. Ordinary table salt can help with this too but Sodium lactate is far more dependable.
Simple Castile Soap Recipe
Makes a 1 lb or 454 gram batch which is exactly six bars if you use this soap mould. Please make sure that you are aware of all the safety measures you need to take when handling lye and making soap. This soap has a 5% superfat.
For more experienced soap makers: you can make this recipe at just above room temperature if you choose. Soaping at room temperature gives you the colour of bars that you’ll see in this recipe’s photos but it will slow down your Trace time. If you’re a beginner, I’d recommend that you stick with the slightly higher temperature given below.
58 g (2.05 oz) Sodium hydroxide (also called lye, Caustic soda, or NaOH)
104 g (3.7 oz) Water (use distilled if you water is hard) — in a heat proof jug
Optional 1 tsp Fine salt or Sodium Lactate
454 g (16 oz) Extra Virgin Olive oil
Fragrance to add after Trace
Optional 14 g (0.5 oz) or 3 tsp Lavender essential oil
Special Equipment needed
- Digital Thermometer or Temperature Gun
- Digital Kitchen Scale
- Stick (Immersion) Blender
- 6 Cavity silicone soap mould
Other Equipment needed
- Stainless steel pan
- Heat-proof plastic jug
- a bowl
- fine mesh strainer
- a spoon
- Rubber gloves
- Eye protection
Natural Soap Making for Beginners
If you’re new to making natural handmade soap, you should read my four-part series on natural soap making. It gives a good introduction on what to expect from ingredients, equipment, cold-process soap recipes, and the soap making process.
Step 1: Making the lye solution
Using a water discount in soap does a few things for this castile soap recipe. It helps stop soda ash from forming, it speeds up the time it takes your soap to ‘Trace’, and it reduces your cure time. The last reason is because there’s less water that needs to evaporate out of the bars.
A more concentrated lye solution will be much stronger though. If it gets on your skin it will burn more and the steam it kicks up won’t be pleasant if you breathe it in. That’s why it’s very important to make your lye solution in a well ventilated area, preferably outdoors.
If you’re using the optional Sodium lactate or salt, stir it in to the lye crystals now. This is an optional step.
With your goggles and gloves on, pour the lye onto the water and stir it in. Keep your face away from the steam that comes up and be prepared for the water to get very hot. Stir until the lye is completely dissolved and then set the jug in a basin of water to cool down. You want it to cool to around 100°F / 38°C
Step 2: Warming the Olive oil
Pour the olive oil into a stainless steel sauce pan and warm it on low until it reaches about 100°F / 38°C. When both the oil and the lye solution are within 10 degrees of one another, it’s time to mix. Take your pan off the hob and proceed to the next step.
Step 3: Stick blending
Pour the lye solution through a fine mesh strainer and into the olive oil. Stir it together and then use a stick blender to bring it to ‘Trace’. Trace is when the soap begins thickening up to a custard or runny-warm-pudding like consistency.
I’ve placed a video at the bottom of this piece to show you the technique I use for using the stick blender. The recipe for the video is one I’ve shared showing how to use Cambrian Blue Clay to naturally color soap. I use short and controlled bursts of stick blending with gentle stirring.
Step 4: at ‘Trace’
You’ve hit ‘Trace’ when you can drizzle some of the soap batter onto the surface of your soap and it leaves a trail. I prefer working at a very light trace since it settles nicely into moulds. A thicker traced soap can literally be spooned up and plopped into containers. If you’re a beginner, aim for somewhere in the middle.
When your soap is at Trace, stir in the essential oil if you’re using it and then pour the soap into moulds. Leave uncovered and at room temperature or pop it in the fridge overnight if you wish. Leave the soap in the moulds for at least 48 hours if not up to four days. Handmade Castile soap can take time to firm up.
Step 5: Unmoulding & Curing
When the soap has definitely hardened up enough, pop it out of the moulds and cure it. There’s very detailed information on how to cure and store soap in this piece I wrote a while back. Thanks to the water discount we used in making the lye solution, your cure time is only four weeks. Using a more standard amount of water in a Castile soap recipe can make the cure time more like six weeks.
Customizing Castile Soap
If you’ve ever traveled to the open markets in the south of France, Italy, or Spain you’ll have seen lots of Castile soap. Most of it is actually Bastile, olive oil mixed with other oils to improve lather, but almost all of it is colored and scented. You can make your castile soap as colorful and as lovely scented as you’d like.
You can literally make this recipe with just three ingredients if you choose — water, lye, and olive oil. The optional lavender essential oil will give it a beautiful floral scent and the Sodium lactate or salt helps to harden the bars.
If you’d like to be more artistic with these bars I’ve collected dozens of different ideas for you in my piece How to Naturally Color Handmade Soap. Keep in mind that the natural color of this soap is a light yellow and that can impact the final color of your bars. Depending on the oil you use, you may find that your soap cures to a bright white color. You can also use different essential oils to scent it and my guide for how much you can use is over here.
If you’re looking for even more soap making recipes and ideas, have a browse through my recipes. This simple Castile soap recipe is just the tip of the iceberg.