Basic cold process soap tutorial

Lemon soap

Difficulty: Intermediate
Time: 1 hour
Yields: 500 g soap

Before starting, please read the safety and precautions post, especially since this tutorial requires the handling of caustic soda!

Cold process soap making is one of the most popular soap techniques. Cold process means that there is no heat added to the process of soap making. As opposed to hot process soap making, during which the soap is cooked to speed up the saponification process (turning the oils into soaps). The heat in cold process is created only by the chemical reaction. You can control this heat during the first 12 hours of the curing phase by either insulating or cooling the soap, but this is a rather advanced technique, therefore in this tutorial we will work with our oils and lye at room temperature and leave the soap to cure without heat control.


The equipment you need for making cold process soap

  • a heat proof polypropylene (PP) jug or container, or a tempered glass jug, like a Pyrex jug for your lye (roughly 500 ml capacity)
  • a microwave proof jug or bowl to mix your soap in
  • stick blender
  • digital scales at 1g increments
  • a 1 litre empty milk/custard/soup carton (I’m using a 1L Campbell’s soup carton)
    or a silicon soap or cake mold with approximate 500 ml volume
  • silicon spatula and whisk

You can buy your material from The Warehouse or Briscoes if you’re in New Zealand, or Big W, Kmart and Target in Australia.


Ingredients you need to make for this basic soap recipe

  • 125g coconut oil
  • 100g olive oil
  • 100g rice bran oil
  • 25g castor oil
  • 53g caustic soda (sodium hydroxide, NaOH)
  • 120 ml water
  • 15 ml essential oil or fragrance

This recipe is comprised of olive oil, coconut oil, rice bran oil, and castor oil. All the recipes featured here on In My Soap Pot are palm free. This recipe is an alternative formulation to the usual coconut/palm/olive trio in soap making, but will still produce a nice solid bar of soap with a rich creamy lather. These oils all offer something different to the soap. Coconut oil will give the soap firmness as well as a fluffy lather. Olive oil adds mildness to the soap. Rice bran oil is added for its skin conditioning properties, which prevents the soap from becoming too drying out to the skin.

If you are using fragrance, make sure it is a fragrance that is skin-safe. Candle fragrances are usually not suitable, unless specified that they are safe to use on skin. Similar when using essential oils: stick to the ‘safe’ essential oils like sweet orange, lemon, peppermint, lavender, rose geranium, cedarwood, lemongrass and stay clear of the more problematic and skin irritating essential oils like cinnamon, wintergreen, etc.

This recipe contains a 5% superfat, which means that 5% of the oils will not be turned into soap and are “free floating” in the soap. Superfatting will make your handmade soap less drying to your skin than commercial soaps, but will also act as a safeguard against caustic soap.

Caustic soda is used for drain cleaning, which is why you’ll probably find it in the cleaning section at your hardware store. Make sure you buy a caustic soda that contains at least 98% pure caustic soda. The other 2% are an additive that prevents the caustic soda from clumping together. A bit like the tapioca starch in icing sugar. Both caustic soda brands pictured above actually tell you that it’s ‘perfect for making soap’, which me wonder if they are bought more often for making soap than for actual drain cleaning!

In New Zealand, you can buy caustic soda from Bunnings Warehouse. Mitre 10 has stopped stocking pure caustic soda a few years ago.

Alternatively, if you live in or near West Auckland, you can also buy your caustic soda directly from Pure Nature, but because it is classed as a chemical hazard material, you have to pick it up from their warehouse in Henderson (no shipping!)

Cold process soap making

  1. Prepare your lye
  2. Prepare your oils and fats
  3. Make soap

There are three main steps in soap making. First, you need to prepare your lye solution. Then, you need to weigh out your oils. And lastly, you pour the lye into your oils and stick blend it to soap. Soap making isn’t complicated, but it does require you to work accurately and safely.

And although this might seem like a simple soap recipe, it will actually teach you the necessary skills to continue on to more advanced techniques. Many beginner soap makers become discouraged because they immediately attempt a difficult and advanced soap technique, rather than starting with he basics. Make a simple batch or two first. (As a little side note, my favourite soaps are just plain simple white, single fragrance soaps!)

SAFETY FIRST: If you haven’t done so already, please read this post about safety and precautions when handling lye and caustic soda. Always wear safety goggles and gloves to protect your eyes and skin!

PREPARE: Before you start, it is helpful to have your material and ingredients set out. You don’t want to be running around looking for batteries for your scales or realising you’ve run out of olive oil!


ONE: Fill a propylene (PP) container or jug or a tempered glass jug with the required amount of water from your tap. If you are in a hard water area (bore or ground water) use distilled water. If you are using rain water or reservoir water, you can use the water straight from the tap. For more information about water and soap making, check out this article!

Weigh out your caustic soda in a separate cup or container.

Then slowly and carefully add the caustic soda to the water. Gently stir, avoiding any splashes, until the caustic soda has fully dissolved and the liquid is clear.

This is now called lye (water + caustic soda). Place the container with the lye solution in the sink and leave it to cool down to room temperature.

You will notice that the lye will get very hot and give off fumes. Make sure you don’t breathe in the caustic fumes!


TWO: Weigh out your coconut oil in the big heat proof bowl/jug/container and place the jug in the microwave for approximately 60 seconds on high, or until the coconut oil has melted.

Weigh out the other oils and combine with the coconut oil. 


THREE: Check if the lye solution has cooled down to room temperature (around 25 degrees C). If the outside of the jug feel cool to touch, it will be at approximately the right temperature.

Carefully pour the lye into jug containing the oils.

Place your stick blender into the oil/lye mixture and start pulsing (turn on the stick blender for about 5-10 seconds and stop, stir the mixture with the stick blender turned off, and then turn it on again for another 5-10 seconds, and so on).

When the mixture has turned a runny custard-like colour and consistency, and you can see no oil streaks in the mixture, your soap mixture is ready and in soap making terms is called ‘at trace’. This is when all the oils and lye have been blended together and emulsified, starting the saponification process (turning the lye/oil mixture into soap).


FOUR: Add your essential oil or fragrance. If you are using fragrance, make sure it is skin-safe (candle fragrances are usually not safe for use in cosmetics). If in doubt ask your supplier!

Give the soap mixture another quick pulse to mix in the fragrance completely. 


FIVE: Pour the soap into the mold and then gently tap the mold on the bench a few times to remove any bubbles that are in the soap. The tapping will help the bubbles come to the surface. 

Let the soap sit in the mold for a few days, before unmolding.

Once the soap is hard enough, remove it from the mold and cut into bars. If the soap is still a bit soft, let it set for a few more days before cutting.

Allow the soap to cure for another 6-8 weeks to completely finish the saponification process (turning the oils into soap) and for all the water contained in the soap to evaporate. The longer you leave a soap to cure, the harder and longer lasting it will become. You can tell when a soap hasn’t been cured long enough because the soap gets mushy in the soap tray!

basic soap making

Basic Cold Process Soap

  • Difficulty: intermediate
  • Print
Before starting, make sure you wear protective goggles and gloves and work in a well-ventilated area, free from any distractions!


  • 125 g Coconut Oil
  • 100 g Olive Oil
  • 100 g rice bran Oil
  • 25 g castor oil
  • 50 g sodium hydroxide NaOH (caustic soda)
  • 120 ml water (distilled if you have hard water)
  • 10 ml fragrance or essential oil of your preference
  • heat proof jugs or containers
  • stick blender
  • digital scales at 1g increments
  • a 1 litre empty milk/custard/soup carton (i.e. Campbell’s Soup) or a soap mould (500 ml capacity)
  • silicon spatula and whisk


  1. Measure out the water in the smaller heat proof jug (i.e. Pyrex) and weigh out the caustic soda in a separate small container.
  2. Slowly and carefully add the caustic soda to the water and gently stir until all the granules have fully dissolved and the liquid is clear. Set in the sink to cool.
  3. Weigh out the coconut oil in a microwave proof jug or bowl and heat on high in the microwave for 60 seconds or until the coconut oil has completely melted.
  4. Weigh out the other oils and combine with the coconut oil.
  5. Once the lye and the oils have cooled to room temperature, carefully add the lye to the oils and stick blend in 10 second pulses until all streaks of oils have disappeared and the mixture has emulsified.
  6. Add the fragrance and stir to blend the fragrance throughout the soap.
  7. Carefully pour the soap into your mold. Keep the soap in the mold for 3-4 days before cutting, and then cure for a further 6-8 weeks.

Where to buy your ingredients and material

  • Pyrex jug, scales, stick blender, whisks and spatulas can be bought from Briscoes or the Warehouse
  • Disposable gloves are available at most supermarkets
  • Your local hardware store (i.e. Bunnings Warehouse) stocks caustic soda as well as protective eye goggles
  • You can buy olive oil, coconut oil, and rice bran oil from your supermarket
  • If you are located in or near West Auckland you can buy your caustic soda from Pure Nature, as well as all your other oils and essential oils for this project


    • Hi Constance! Unfortunately corn starch and corn silk are two completely different things. Corn starch is made from grinding corn kernels. Whereas corn silk is the stigma of the corn flower, and contains many beneficial proteins and minerals. It’s not really something you can substitute in this case. But if you use papaya, you could omit it. Hope this helps!

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