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 taken. 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 helps to stabilize 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 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 mold, 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. Just be careful that you don’t use too much sodium lactate or it can cause your soap to go crumbly.
Using less water than what’s typical, is called using a water discount. In soap does a few things, including help stop soda ash from forming and speeding up the time it takes your soap to ‘Trace’. It also reduces your cure time since there’s less water that needs to evaporate out of the bars. In this castile soap recipe, using a water discount will be helpful on all counts.
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 to what to expect from ingredients, equipment, cold-process soap recipes, and the soap making process.
Simple Castile Soap Recipe
Makes a 1 lb or 454-gram batch which is exactly six bars if you use this soap mold. 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 color 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.
Simple Castile Soap Recipe
- Stainless steel pan for melting the solid oils
- A large bowl for measuring the liquid oils into
- 16.01 oz Extra Virgin Olive oil 454 g
- 0.49 oz Lavender essential oil Optional / 14 g / 3 tsp
Prepare your work station
- Prepare your workstation with your tools and equipment, and have your mold at the ready. Put on rubber gloves, eye protection, and an apron. Carefully pre-measure the ingredients. The olive oil can go in a small stainless steel pan, the water into a heat-proof jug, and the lye in another container. If you're using it, pre-measure the essential oil into its own small dish or ramekin.
- Although listed as 'optional', sodium lactate is useful in hardening all soap recipes, especially softer soap like this castile soap recipe. It's available as a powder or in liquid form and if you're using the liquid form, you'll need one teaspoon of it. If you're using the powder form, use only half a teaspoon and dilute it in one Tablespoon of the water amount you've measured for the lye. Do this before you begin, and mix the powder and water into its own small dish.
Make the Lye Solution
- Make your lye solution in a well-ventilated area, preferably outdoors, by an open window, or under a kitchen extractor that ventilates to the outdoors. 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 100°F / 38°C and can begin warming the olive oil as it cools.
- Add the sodium lactate to the lye solution after it's cooled below 130°F / 54°C
Warm the olive oil
- Warm the olive oil in its pan on low until it reaches about 100°F / 38°C. When both the oil and the lye solution are within about five degrees of one another, it's time to mix. Take your pan off the heat and proceed to the next step.
Stick blending to Trace
- Pour the lye solution through a fine-mesh strainer and into the olive oil in the pan. Stir it together and then use an immersion blender (stick blender) to bring it to 'trace'. Trace is when the soap begins thickening up to a warm and thin custard-like consistency.
- Using the stick blender to emulsify small batches of soap can be a little more tricky than larger batches. I recommend that you first dip your immersion blender into the pan and with it turned off, stir the mixture. Next, bring it to the center of the pan, and with both your hands, hold it on the bottom of the pan and blitz it for just a couple seconds. Turn it off and stir the soap batter, using the blender as a spoon. Repeat until the mixture thickens up to '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 molds. A thicker traced soap can literally be spooned up and plopped into containers. If you're a beginner, aim for somewhere in the middle.
- Just to clarify, in small batches of soap I advise that the immersion blender is not moving while you have it turned on. Hold it down against the bottom of the pan and turn on to pulse. Only stir when the device is off, as stirring while it is on will create air bubbles and kick up caustic soap batter.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.
Molding and Curing
- When your soap is at trace, stir in the essential oil if you're using it (here's further information on other essential oils to use) and then pour the soap batter into molds. Leave uncovered and at room temperature or pop it in the fridge overnight if you wish. Leave the soap in the molds for at least 48 hours if not up to seven days. Handmade Castile soap can take time to firm up. If in doubt, just leave it a bit longer.
- When the soap has hardened, pop it out of the molds and cure it. Space the bars out on wax paper / grease-proof paper someplace airy, dim, and room-temperature. This will allow the water that's left in the bars to gently evaporate out. There's detailed information on how to cure and store soap in this piece. 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 to eight weeks.
- Once made, your castile soap will have a shelf-life of up to two years. Check the oil bottle that you're using though -- the best-by date on the olive oil bottle is the best-by date of your soap. If your handmade soap is destined as gifts, check out these eco-friendly soap packaging ideas.
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.