How to make Soap, Hot Press Style – Workshop Notes

These notes are designed to follow on from my Soap Making Workshops. If you have not attended a workshop you can still read through the notes, then follow the recipe and instructions to make your own soap. Make sure you follow the recipe exactly, so all the caustic soda/ lye is used up and your soap is safe to use on your skin. Feel free to ask any questions if you’re unsure about anything.

• Slow cooker or ‘crock pot’.

• Scales
• Bucket/suitable container for mixing.
• Measuring jugs
• A stick blender (immersion blender)
• Spatula
• Baking parchment paper
• Loaf tin or jelly moulds for soap shapes – silicone moulds are great.
• Optional Extras – essential oils to fragrance and flowers to decorate

• Wear professional safety equipment, to protect yourself when the sodium hydroxide is used – goggles, gloves and a mask are essential once you begin using the sodium hydroxide.
• Use solid stainless steel or polypropylene for mixing sodium hydroxide in.
• Ensure you are in a well ventilated space so you are not breathing in the fumes from the sodium hydroxide.
• Make the soap at a time where you will not be distracted and there are no children or pets around.
• Use the exact amounts in the recipe to ensure all the sodium hydroxide is used up when the soap is complete and ready to use (see below for how to tweak the recipe)*

Soap Recipe

  • Spring Water – 380g (do not use tap water)
  • Sodium hydroxide (caustic soda/ lye) – 137.40g
  • Olive oil – 650g (do not use pomice olive oil)
  • Shea butter – 80g (for creaminess)
  • Coconut oil (not fractionated) – 270g (for bubbles in your soap)
  • Orange essential oil – 30g
  • Calendula (marigold) petals – hand full.

• Prepare the loaf tin or container by lining it with parchment paper – if you are using silicon moulds they won’t need lining.
• Weigh all the ingredients out.

• Put the oils & shea butter in the slow cooker first on a low heat so they gently melt.
• At this point make sure all your safety gear is on and there are no distractions, then in a separate container, add sodium hydroxide (caustic soda/ lye) to water, this causes an exothermic reaction, making the mixture heat up very quickly. Never add water to sodium hydroxide as it will be too concentrated initially and could bubble up. Because of the fumes that are produced, at this point, I often do it outside if there is a safe and suitable space. DO NOT GET THE MIXTURE ONTO YOU!
• Stir the sodium hydroxide and water, initially it appears cloudy, wait for it to become clear and then add it to the oils & shea butter in the slow cooker.
• Use the stick blender to blend everything until it leaves a ‘trace’. This means, when you drip the mixture you can still see the impression it leaves behind in the mixture.

This is the point that you would pour the soap if you were making cold pressed soap.

For hot pressed soap, you leave the mixture in the slow cooker, on a low heat with the lid on for 15-20 minutes.

Set a timer so you remember to return and check the mix.

When you return, the mixture looks like the fat has separated from the liquid. Use a wooden spoon or spatula to mix everything together again, and then leave it for another 15-20 minutes.

When you return this time, the mix looks like vaseline or apple sauce, and will have lots of air through it. Stir everything together again.

The mixture is still very hot so take care.

Turn off the heat on the slow cooker.

• You can now add in the essential oil** and blend  it evenly through the mixture (optional).
• Sprinkle calendula petals into the mixture and stir through evenly (optional) (calendula / marigold petals keep their colour when added to the mix, others usually turn brown).
• Pour into the loaf tin/ soap moulds. Decorate with dried petals (optional).
• Leave for 24 – 48 hours to allow the soap to set before cutting into slices or whatever shapes you want. If you have used silicon moulds pop the soap out.
• The soap is now ready to use.

The Science bit – the ingredients go through a chemical process called saponification to turn into soap. The acid (in this case the oils) mix with the sodium hydroxide. This usually takes between 24-48 hours but the hot process method speeds this up by keeping the mix heated and it is not necessary to cure for weeks, it is usually ready to use in 24 hours. During the saponification process glycerol is released from the fatty acids allowing them to combine with the hydroxide ions creating soap. The release of glycerol results in glycerin in the finished soap.

**Essential oils do not usually hold their therapeutic benefits in the soap making process, but they are a natural way to bring a fragrance to the soap. I usually use citrus or lavender essential oils in mine. Click to check out this interview with Robert Tisserand on what happens to essential oils in soap making.

*Recipe adjustments
If you want to adjust the recipe or design your own, then I recommend using the online tool:  Soap Calc** – this is because each ingredient has it’s own saponification value which means it will need a specific amount of sodium hydroxide in the soap. You can enter your recipe into the tool and it works out for you the correct ratio of ingredients to ensure all the sodium hydroxide is used up during the soap making process. For example if you want to replace the olive oil for apricot oil in the recipe above everything else will need adjusting to make sure the final product is safe for your skin.

Super Fat – if you hear this term, it means there is more fats and oils in the recipe than will be used in the saponification process, which means the final product leaves your skin feeling nourished and moisturised. This recipe has a super fat value, and you should notice that the soap does not dry your skin or leave it feeling stripped.

**Click here to check out this YouTube video on using the tool Soapcalc.

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