How To Make Soap – Cold Process

In my previous posts I have often spoken about various processes involved in making soap.  In this post I will describe how to make soap using Cold Process.

Cold Process seems to be the way most people make soap and is certainly a straight forward method.  Many people use it because it is not only arguably the easiest method and therefore ideal for starting out, it also allows a lot of freedom in how the soap looks which makes it a mainstay for the majority of artisan soapers the world over.

I won’t go too much in to the science behind making soap in this post, but when oils and fats (slightly acidic “fatty acids”) are combined with Sodium Hydroxide or Potassium Hydroxide – both are also referred to as Lye (strong alkalis) – they go through a chemical reaction that leaves us with soap and glycerine.  For the purposes of this post I will just say “lye”, but most bar soap is made with just Sodium Hydroxide.  Liquid soap and many shaving soaps use Potassium Hydroxide.

I will mention, however, that lye working with lye is something to approach with caution.  It can cause serious damage if not handled correctly.  Thankfully, correct handling is not overly difficult – if you are comfortable with how you should handle containers of scalding hot water and some of the more powerful cleaning products, then you should be comfortable handling lye. Make sure that all children and house pets are not going to get underfoot or interfere with any part of the process or ingredients at all before you begin. I have read stories of children pulling containers of lye solution off of the kitchen worktop and spilling it all over them……….no one wants this.

Soap in an area where you have fast access to running water. If you spill some lye on you, rinse it with cold water for 10-15 minutes and seek medical advice. Some people will suggest using vinegar as it neutralises the lye – it is true, it will do this, but in doing so it will cause a lot of heat which will likely cause you heat burns on top of your chemical burn. By using water alone, you quickly dilute the lye to a safe amount and also wash the solution from your skin.

When soaping, you will need some specialist equipment (I have written a post that goes in to what you need)  including safety equipment for working with lye.

Now, if you haven’t been scared off……………………

As I have mentioned before, getting the right mix of fats for your soap is in theory very easy but in practice can take a lot of work.  Some soapers are constantly making adjustments to a recipe to get that perfect combination and many (especially people who sell soap) guard their recipes well.  After all, they put in the hard work to develop the recipes!  Many books on soaping contain recipes to follow, but a few words of caution – not all recipes in books will produce safe soap.  Printing errors can happen so it is worth checking everything on a good lye-calculator (more on that in a moment).  Also, avoid any recipe that does not measure everything by weight.  In soaping, everything should be measured by weight rather than volume, so that is a tell-tale sign that things might not be quite right.

One source which would whole-heartedly recommend is the Soap Making Forum – here you can find a lot of interesting information and some jolly helpful fellow soapers.  It is where I learnt almost everything that I know about soap making and is an invaluable resource for ideas, feedback and advice.  I admit to plugging the site somewhat, but I feel it is worth while as it really does offer a lot to soapers.

Once you have your ideas for oils to use, you need to work out how much lye you need – this is where a lye calculator (mentioned earlier) comes in. Different oils need differing amounts of lye to saponify.  So 100g of olive oil needs a different amount of lye than 100g of coconut oil, for example.  This is one of the most important parts of soap making!  While the choice of oils is important and will impact your finished soap, if you make a mistake with the amount of lye you could end up with a harmful soap.

With both the oils and the lye, accurate measurements are required. Analogue scales are really not up to the job at all – digital is much better for soaping. Take your time and get to know how quickly yours reacts as some have a bit of a delay before they register the new weight which can often lead to adding too much in to the pot. Remember, you can easily put more in but it is much harder to take it back out again!

So on to the actual method itself.  Please always refer to the article on soaping equipment I linked to before and bear in mind, this is just one way of many – there are so many variations at certain steps, but this process will work as it is one that I use myself:

  • Measure all of your oils and fats in to a good saucepan, making sure there is enough room
  • Put it on the hob on a low to medium heat and remove from the heat when melted
  • Meanwhile, measure out your water for your lye solution in to a container suitable for a hot lye solution
  • Measure out your lye in to another container
  • In a well ventilated area, slowly pour the lye in to the water – it will produce fumes and get very hot.  Do not breathe the fumes!  Do not pour the water in to the lye as this can cause it to violently react and could cause you a lot of harm!
  • Stir the lye mixture until all of the solids have dissolved

Many books will tell you that the lye and the oils need to be at such-and-such a temperature before you combine them.  This is not strictly true, but for starting off it is good to have a reference point.  Having both oils and lye solution between 30-50 Celsius should be fine.

  • Pour your melted oils in to the pot in which you will mix the soap
  • Slowly pour the lye solution in to your oils.  It is important that it is done in this order, not the other way around
  • With your stick blender, stir the mixture and turn the mixer on and off in short bursts as you stir – you might need to shake the mixer once it is in the batter before you turn it on to remove air trapped in the blade area
  • Mix in this fashion until you reach trace

Trace.  There is a term that needs some defining.  It is an old candle making term and it basically refers to when a mixture is so thick that it leaves a ‘trace’ behind when stirred up.  Think of the difference between a cup of tea and a pot of yogurt – you can stir tea but it is so fluid that it will end up bearing no signs of what you just did.  A yogurt on the other hand, will.  You can see where the spoon was and when you drop some of it back in the pot you can see where it doesn’t quite all end up fully mixed in again.  That is trace, when there are traces left behind from the thickening mixture.  There are different stages of trace, too – from light trace (barely any signs) through to thick trace.

  • For our purposes, mix until you can clearly see where the stick blender was.  The soap batter should stick to the blender quite nicely, too.
  • Pour the mixture in to your mould

The batter will generate heat as it saponifies (becomes soap) and this can change the soap, especially on the inside where it is insulated by the rest of the batter.  This is called ‘gel’ and changes how the soap looks and how it cures.  It does not make a major difference to how the soap feels when used, though.  Many people try to keep the soap colder to prevent this or they make sure the soap gets hot enough to change it all.

  • Check on the soap from time to time – there will come a point when it is hard enough to take it out the mould but still soft enough to cut
  • Be careful, the soap can still be saponifying and so you should wear gloves when handling it – it could still be caustic!

Soap needs to cure – more time for any lye to react with oils, but even more than that as the structure of the soap changes over time.  At least 4 weeks is good for a normal soap, but those high in olive oil will need a lot longer.

Te see if you soap is safe to use, you can perform what is known as the “zap” test.  Remember holding a 9v battery to your tongue?  It’s a bit like that…………..

………….take your soap, wet a finger and rub it on the soap so there is a layer of soapy water on your finger – wait a few moments to see if there is a tingling feeling.  If not, put the finger on the end of your tongue and see if there is a zapping feeling like with the battery.  When all is well, actually touch the soap itself to your tongue – if there is still no zap, you are safe to use it on your body.

Congratulations – you just made soap!

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