Cold process vs hot process

Cold process vs hot process… at some point, each soapmaker asks which one is better or when they should be used.


But before I give you some arguments, I will explain these two techniques a bit more in detail it is crucial for understanding their advantages and disadvantages.


If you are a total beginner – I suggest you to go for the cold process with simple recipes.
Cold process and hot process are the two basic techniques in making home-made soap from scratch. I say from scratch on purpose, as there are two other methods of making soap at home (see this post).


There are many variations of these two techniques and I will dedicate to these one of my future posts.

Cold process vs hot process


Both techniques have three common steps:


1) Preparing the lye solution (dissolving NaOH or KOH beads/flakes in a distilled water)

2) Preparing the oils (melting solid fats and mixing them with liquid oils)

3) Pouring lye into oils and stirring until an emulsion takes place (the emulsion state is called somewhat unfortunately a trace, which leads often to confusion of a beginner soapmaker…)


At this point (how can we recognize an emulsion will be a post on its own), the two techniques differ:

  • In the CP – cold process technique:

4) Fragrances/essential oils, colorants and other additives are added to soap

5) The soap is poured into molds, where saponification is finished within 24-48 hours. Often, the molds are insulated, as the heat generated in the reaction speeds the saponification

6) The soap is unmolded and cut into bars (if block mold was used)

7)  Bars of soap are left to cure for about 2 weeks. During this period, water loses water and further hardens. If within the first 24-48 hours soap did not pass the gel phase, this period ensures full saponification.


  • In the HP – hot process technique:

4) The soap is further heated in a crockpot or a double boiler, on low heat somewhere between 140°F (60°C) and 176°F (80°C)

5) After the soap reaches the stage called the gel phase (which can take 1-2 hours), the heat is turned off and additives are added (fragrance, colorants, other).

6) Then the soap is poured – or often rather spooned – in the mold (soap that passed the gel stage is very viscous)

7) After the soap cools down, it is unmolded and cut (if necessary)

8) Soap is let to cure for a week-two – during this period some water evaporates, soap hardens and gains on bathroom sink life (is used up slower).

Which soapmaking technique to choose?

I bet many soapmakers will find a ton of arguments why their preferred method is better, but here is what I think – no one is really better than the other – both have their advantages and disadvantages.
But let’s have a bit of fun and simulate here an argument exchange between a cold-process soapmaker (CP) and a hot-process soapmaker (HP):
CP> Cold process is faster to be poured in molds – it takes less then an hour, while in hot process you have to stand over your crockpot for at least 3 hours! That is way too long…
HP>  First, I do not have to stand over the crock pot,  I just occasionally check on it , it  works on its own.  
Second, yes, maybe it takes 3 hours to pour into molds, but after that the saponification reaction is finished and I can use my soap pretty much right after.  
You have to wait 24h for unmolding and then 2 weeks for it to cure!  Well, that is way too long!
 CP> Yes, but what is it for – being able to use it directly – when you however have to let it cure for 1-2 weeks so that it evaporates some water so that it does not use up too fast…
Moreover, if I insulate my mold properly, also my soap passes the gel phase and after 24 hours has a correct Ph. And you know, the gel phase is not always wanted.
I prefer the structure of an ungelled soap – it is smoother.
And then, did you ever try to make a white bar of soap? Impossible with the HP and gel phase, as it always darkens the soap substantially…
HP> Ok – for a white soap, cold process may be the best technique, but how many times I really do want to make a white soap?
As for the structure – that is really a personal preference, and and as for getting used up too soon – you know that according to experiments of K. Dunn, the gelled soap resists better to water than the ungelled soap?
In addition, I  usually get very impatient to try the soap I just made and really don’t want to suffer from the ICPSDHS  (the impatient cold process soapmaker dry hands syndrome)…           
CP> You have made some good points, but still – I love to create nice and complicated swirls in my soap and I really cannot imagine how to achieve this with the sticky hot process soap… not to talk about the ever present air bubbles in the final bars
HP> One can make some nice patterns with HP, too, its just a question of practice. And again – not everyone needs to swirl…
 But if you  want to make a transparent or liquid soap, you have to hot process – transparency needs  a really complete gel phase!
CP> Right, the hot process technique is necessary for a transparent soap, but attention – you still can make a liquid soap by cold process, although not transparent.
HP> Maybe, but the hot process has another advantage – the fact that at the time you add additives the soap is pretty much finished, you do avoid unpleasant surprises of fragrances/essential oils accelerating your trace so fast, that your soap coagulates within seconds and you can only literally PUSH it in the mold, praying for not having any unreacted lye pockets in it….

CP> This just needs a bit of practice and information – if you know that some fragrance oil can accelerate your trace, you can prepare for it – by adding more water to the recipe or mixing your fragrance oil with oils prior to mixing with lye, not using the blender just hand stirring...


HP> But there is more – in the hot process, you can add fragrances/essential oils sensitive to alkaline conditions of the CP process, without them loosing the scent. For the same reason, you need only half of their quantity!


CP> Humm, true, but you have to pay attention to your temperature, so that it does not exceed the flash point of the essential oils  you add, or they will evaporate!



And in addition – with CP, you can make a whipped soap – that floats on water – and a cream soap – that looks and feels like a real cream!

HP> It seems that both techniques are an important part of home-made soapmaking…
CP> I fully agree!


Which of the methods would you choose? 🙂 I am sure there are more arguments on both sides – I will be happy if you leave me a comment with your point of view!