How To Make Castile Soap At Home

Here’s how to make Castile soap, a traditional olive oil soap recipe that’s absolutely one of my favorites. It’s simultaneously one of the most inexpensive soaps you can make (making it a great beginner soap), but also the most gentle of cleansers at the same time. 

This is a cold process solid soap, not to be confused with my liquid castile soap recipe which is also great for sensitive skin.

When I have my grandkids over I always get them to use my homemade Castile soap as it’s so much kinder on their young skin than any other soap I can make.

In fact, if I know anyone who’s just had or is about to have a baby, I give them a boatload of this soap (minus any essential oils) so they don’t have to worry about going out and buying specialist baby soap, which is damn expensive as well.

Castile Soap v Bastile Soap

Throughout its history, Castile soap is ordinarily made with 100% olive oil, which is one of the reasons it’s so pure and mild on the skin. However, in recent years, soapmakers have started making what has been coined ‘bastile soap’.

Bastile is your standard castile soap recipe but adulterated with a small quantity of other oils and/or cosmetic butter to enhance the skin-softening and nourishing qualities. Bastile is usually 80-95% olive oil, with the 20-5% additives being anything from shea butter to macadamia nut oil. Basically, whatever you wanna put in it!

There’s also another key reason you might favor making bastile soap over castile and that’s because bastile is a lot firmer than it’s purer sister soap. Castile can sometimes melt quite quickly when exposed to warm water. So, instead of lots of your lovely soap ending up down the sink, bastile affords you much more ‘lather time’, for the lack of a better phrase.

So, I thought it might be fun to share with you two of my favorite recipes, castile and bastile, all in one little blog post! Then, you can give both a try and see which one you prefer. So let’s kick things off with the traditional castile and come on to bastile in a little bit.

One thing I should note is that Castile has quite a rich, creamy texture to it. This is predominantly because of the high oil content and lack of other ingredients such as cosmetic butters. It almost feels like a lotion bar! Bastile is very similar, although a bit less creamy and easier to lather.

About Ingredients In This Castle Soap Recipe

You’ll notice here that the amount of water I say to use in this recipe seems a little low. Usually, I opt for a ratio of 1:2 (lye to water), but this recipe doesn’t even come close to that. In fact, if you run this recipe through a lye calculator, it might tell you to add a lot more water than I’ve recommended. However, you really don’t want to do this.

Do you remember when I said Castile is quite soft? Well, it also takes a very, very long time harden in the mold. By decreasing the amount of water we add, this recipe behaves much more like your standard soap recipe and you should be able to remove from the mold in about 24 hours to cut into bars. Business as usual!

For Little Ones & Babies

As I’ve already said, castile is great to use on your little ones, especially babies, as it’s the most gentle of cleansers you could possibly use besides water. If this is what you intend to use it for I recommend to omit any essential oil. Fragrance-free is always the best in terms of purity, especially for your little baby.

If your kids are a little older, you could get away with using a small amount of essential oil but I would still never use a synthetic fragrance oil on a child who’s skin, body and brain are still developing. There are still many unknowns when it comes to synthetics, particularly fragrance oils.

The research just isn’t there yet, and we have no idea how a synthetic agent such as fragrance oil can affect the developmental physiology of a young child. So, I would rather not risk it. If you want to use essential oil, I’d recommend ones that aren’t overly expensive or potent, such as lavender or sweet orange.

Unsuited To Fragrance Oils

Moreover, I find that this recipe is just totally unsuited to fragrance oils in general. I really struggle to use them, as it makes the batter seize like crazy! Take my advice and just use an essential oil instead. Or, don’t use either.

As this recipe is so simple, with literally only olive oil besides our lye solution and essential oils, there’s very little to substitute here. Bastile soap allows for more freedom, so if you want to get creative scroll down to give that one a try instead.

How To Make Castile Soap That’s Gentle On Skin

This DIY Castile soap recipe is absolutely one of my favorites, it’s a traditional olive oil soap that's a gentle cleanser & very inexpensive to make. 

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Prep Time: 30 minutes

Active Time: 30 minutes

Curing Time: 28 days

Total Time: 28 days 1 hour

Difficulty Level: Intermediate

Yield: 8 Bars (approx)

Author: Angela Wills

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Ingredients

1/21x2x3x

MetricUS Customary

Oils & Butters

• 900 g Olive Oil
• 172 g Distilled Water

Lye Solution

• 115 g Soapmaking Lye (caustic soda)
• 35.5 g Essential Oil

Equipment

• Silicone Soap Mold
• Soap Cutter and Box
• Basic Stick Blender
• Lazer Temperature Gun
• Digital Scales
• Safety Glasses
• Long Rubber Gloves
• PH strips for safely testing acidity
• Large stainless steel pan
• Large plastic /glass jug or plastic bucket.
• Spatula
• An old towel

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Instructions

• If you’ve not made soap before, take a look at my full cold process tutorial here.

  Make sure you are making the soap in a well-ventilated area. Put on your gloves and eye protection, your mask, apron, and long rubber gloves.
  
• Weigh out your essential oil, olive oil, distilled water and lye crystals in separate containers (use glass for essential oil) ahead of time. It makes things a lot easier.

  The lye crystals and in turn the lye solutions and subsequent soap batter are all very caustic and can cause nasty chemical burns, be safe and use your PPE.

  Then, go ahead and pour your lye crystals into the distilled water. Make sure to pour the crystals slowly into the water to avoid splashing. As you pour, turn your head and try to lean away from it slightly so that if splashes do happen, you’ll avoid it more easily. Stir carefully with a stainless steel spoon.

  This will begin the chemical reaction and your lye solution should rapidly increase in temperature. Place to one side, ensuring the room is well ventilated. Be sure to not breathe any of the fumes in, as they are quite toxic.
  172 g Distilled Water, 115 g Soapmaking Lye
  
• Pour your olive oil into your chosen glass or PET plastic mixing bowl that you use to whisk up your soap batter, then pop it into the microwave to heat it up. You want it to be within 90-140F.

  Now we need to balance the temperature of the oil and the lye solution. Using a laser thermometer, check the temperature of your lye solution. If it falls between 90-140F, you’re good to pour. If it’s too hot, wait a little while and then pour. If, during the time you’ve waited for your lye to cool, your oil has cooled too much just pop it back into the microwave to get it back up to between 90-140F.

  Once you’re happy that both your lye and your oil are between this temperature range, pour your lye into the oil. Make sure to do it this way around, as you want to avoid splashing and losing any of the oil to the rim of the bowl.
  900 g Olive Oil
  
• Using a stick blender, blend the soap batter until you reach a light trace. You will notice immediately that the color of the oil has changed to a creamy, yellowish hue. This is called emulsion and is the precursor to trace.

  If you’ve made any other type of soap before, you may notice that this soap takes a lot longer to trace than others. This is fine and totally normal, just keep blending until you can pick up some of the mixture with a spoon, ladle it back onto the surface of the batter and it doesn’t immediately emerse. It should just sit on top. If you want a better description of trace, take a look at step 5 of our basic soap recipe.
  
• Now that we’re at trace, it’s time to add our essential oil. Go ahead and pour the whole 35.5g into the batter and give it another blend. Be sure to work quickly, as all soaps have a tendency to seize when adding essential oils after trace.

  Once you’re happy that the essential oil has fully dispursed, move on to the next step.

  If you’re making a baby-safe, essential oil-free version, ignore step 5 and skip immediately to step 6. Although you may wish to blend a little longer than normal so it’s a little thicker than a light trace.
  35.5 g Essential Oil
  
• Working quickly but carefully so not to let the batter harden in the bowl, pour or spoon your batter into your soap mold. Once you’re happy you’ve got all of your mixtures in the mold, cover the top of the mold with a cut to size piece of cardboard and wrap with an old towel that you use only for this purpose (never use it to dry skin again, even if washed in a laundry machine).
  
• Leave to harden in the mold for 24-48 hours. Then, you can remove from the mold and cut into bars.
  
• Depending on the thickness of the cut, you should be able to get between 6-10 bars.
  

Category: Soapmaking

Cuisine: N/A

Difficulty: Intermediate

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The Bastile Soap Recipe

Ingredients For Bastile Soap

Lye Solution

• 171g Distilled water
• 114g Sodium hydroxide crystals/caustic soda

Oils and Butters

• 765g Olive Oil
• 135g Shea Butter
• 35.5g Essential Oil

Notes on ingredients

As I said earlier, bastile soap is much more versatile due to the inclusion of other oils besides olive. When substituting the shea butter, you can use any cosmetic butter you prefer. Cocoa, mango and illipe are all good alternatives to shea. If you like, you can substitute some of the shea for various base oils that you enjoy or want to try. Be careful to make sure that you have no less than 80% of your oils and butter mix to be olive oil, as otherwise you’re not really making bastile soap at all.

Important note! If you do intend to sub some of the ingredients, keep in mind that you will need to run it through the sap calculator in order to make sure you’re using the right amount of lye. Nonetheless, I would stick to the amount of water I suggest and always check the PH before using it.

Like with castile, feel free to experiment with whatever essential oil blends that take your fancy. Although remember that if this is intended for young children, make sure not to use certain essential oils. If this soap is for a baby, you may want to avoid using any essential oil at all and keep it scent/fragrance-free for their super sensitive skin.

Method

Follow all the steps I’ve listed above for homemade castile soap, although you will need to melt the shea butter. You can do this by simply combining the shea and the olive oil in step 3. Ensure that the shea is fully melted, and the oil/butter and lye solution are at a balanced temperature of between 90-140F before combining.

Final Thoughts

So there we have it, how to make castile soap in two ways, that will cost you very little to make! This particular recipe is a great one to learn, simply because the ingredients are so easy to get your hands on and is always my go-to if I’m low on certain ingredients.

I’ve been perfecting how to make castile soap for years now, and I’ve only recently started using significantly less water. I have to say, I’ll never go back to the amount of water I was using before. If like me, you make a lot of soap, it’s really annoying having to wait around for liquidy batter to harden in the mold.

When I have a million and one different recipes I want to try, I just don’t want to wait around to use one of my molds again. I guess if you had a ton of molds it wouldn’t be so bad, but for someone who doesn’t make this to sell buying lots of molds is not a great investment.

My family absolutely loves this castile soap (which is great considering how it’s a lot cheaper to make than any other). I’ve absolutely committed it to memory now, and I encourage you to do so as well.

If you give this recipe a go, totally let me know how you got on. I love to hear all of your soaping stories, especially when something goes wrong so I can try and help you out. I also love hearing what fragrance and essential oil blends you use, it’s fun to experiment and find new amazing aromas!