If you make your own products and toiletries you will no doubt have already heard about , given that it’s a major ingredient in pretty much every online recipe out there! I use bar and liquid Castile in a whole array of products ranging from foaming hand-wash, to toilet cleaner, laundry detergent and dish . is so popular and widely used in green cleaning products because it is considered to be one of the safest and most environmentally friendly cleansers around. It’s natural, biodegradable and totally free from the petrochemicals, oleochemicals and other synthetic nasties found in many detergents. It does have one major drawback however…it’s expensive. A 140g bar of Dr Bronners will set you back around $5.50 here in Australia, so grating a few of those into a DIY laundry detergent recipe can turn a frugal homemade product into an expensive luxury item. Thankfully you can make the same sized bars of at home from scratch for $1.09 or $0.59 if you don’t mind them being unscented.

Finding the ideal homemade 100% Castile recipe can be tricky and coming up with something that worked for us took a lot of time and experimentation. Our trial batches ranged from soft and oily, to brittle and crumbly. One batch looked great but when I picked it up in the bathroom to clean up after gardening it felt like trying to wash my hands with a mini-paving slab! Finally, we came up with the recipe outlined below, which we are very happy with. It  produces about 2kg of 8% superfat 100% soap. If you want to tweak the batch size of this recipe or try different oils to increase lather, it is essential to put it through a calculator (you can find one on the Australian soap makers website). A word of warning though, adding a combination of oils and other ingredients such as stearic acid can shorten cooking time and seriously alter the characteristics of the soap so you will be back in the experimentation zone!

What you need to make bars of Castile Soap

– 1500g Olive oil
– 450g 
– 187g Lye
– Sodium Hydroxide (NaOH)

– Heat safe container for lye/water mixture
– Heat safe spoon
– Accurate scales
– Stick blender
– Crock pot
– Safety equipment: glasses, gloves, overall/ long sleeved shirt

Step 1. Pour 1500g olive oil into a crockpot placed on a set of scales

Step 2. Set your crock pot on high heat setting and let the oil heat up.

Step 3. Put on safety equipment and weigh out 187g of NaOH

Step 4. Pour 450g of distilled water into a large heat safe container

Step 5. Add the NaOH to the distilled water. It is very important to add the NaOH to the distilled water NOT the other way around

Step 6. Stir with a heat safe spoon until the NaOH is dissolved. This step should be undertaken outside or in a very well ventilated room as you don’t want to be breathing in the fumes.

Step 7.  Once the cloudy NaOH solution has cleared, it can be added slowly into the crockpot.   This can be done while the solution is still hot and while stirring the heated oil continuously.  During the cooking process the heat may need to be varied.  If the mixture is bubbling up to a point where it might overflow turn the heat off until the bubbling has subsided.

Step 8. Using a stick blender pulse the mixture intermittently for about 10 minutes until a thick trace has been reached (consistency of thick custard). Continuous use of the blender will result in it overheating.  While making liquid soap for the first time I inadvertently almost melted the blender so I definitely recommend letting it cool between periods of pulsing!

Step 9. Once a thick trace has been reached, cover the pot and turn down to the low heat setting.  Only remove the lid to stir every 20 minutes. Do NOT be tempted to keep stirring with the lid off – it is absolutely crucial that the lid remains on.

After about 40 minutes it should start to look like runny mashed potatoes.  As the mixture thickens up the stick blender will become redundant and continue with the spoon.

Step 10. While waiting between stirring, it may be a good time to line the soap mold in preparation for your completed batch.  For details on making your own mold and lining it click here.  In this case I have reused the lining from the last batch, saving on time and resources.

Step 11.  After 1-2 hours of cooking it should be almost ready.  Once the consistency is thick Vaseline texture, glossy and slick.  Turn the crock pot off.

Step 12. Optionally, any colour or fragrance can be added.  Mix thoroughly.  In this batch 30g of lavender oil was added

Step 13. Place into the mould in large spoonful’s.

Pound the mould on the counter to ensure it packs tightly into the corners of the mold and a gloved hand can be used to aid in the elimination of any air pockets

Step 14.  Let it sit overnight.  The next morning the mould can be removed and the soap sliced with a sharp knife


Step 15. Place on a rack for curing.  Each bar should ideally be left to harden for a couple of weeks.  Curing time will again vary depending on the ingredients used.

The 100% olive oil soap is slower to come to trace and cooking time has a tendency to be longer. In my first few batches I was tempted to keep stirring with the lid off for long periods but the soap was not turning out right.  The mixture was drying out and I was overcooking it.   The three most important points that I have found greatly improved my results making hot process castille soap are:

  • heat up the oil before combining it with the NaOH solution (be careful not to heat the oil up too high or the mixture will boil over when added together) to increase the rate at which trace is reached
  • only remove the lid to stir every 20 – 30 minutes
  • transfer to the mold as soon as it reaches the thick Vaseline stage

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  1. Lovely looking soap! Thank you for the thorough tutorial! I was wondering if you could describe the lather for ma and tell me how long these bars last compare to other bars. Also, have you ever made liquid soap with these bars?

    Thank you again! Looking forward to the other gems I’m sure to find on your site!!

    1. Glad you liked it! This soap cleans well but does not have a great deal of lather. For more lather its best to use a mix of olive oil and castor oil rather than just pure olive. The bars last as long as other bars. We haven’t made liquid soap from the bars, we make our own liquid soap. Bar soap uses sodium hydroxide to saponify oils whereas liquid soap uses potassium hydroxide. When you use bars to make liquid it tends to continually try to solidify. Soap made using potassium hydroxide remains liquid but is very fussy to produce and takes a lot of time. Hope this helps!

  2. I use my bars to make liquid soap too. Just grate them and add water gradually until it reaches the desired consistency. It’s lovely

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