Does temperature matter in soap making? - The Soap Coach
does temperature matter in soap making

What temperature should my oils and lye be?

What happens if they are too hot or too cold?

How can I avoid volcanoes in hot process soap making?

So many questions are asked about this subject and yet I doubt you will get the same answer from every soap maker. Everybody has their own way of doing things, their own preferences and annoyingly they are all probably right in the answer they will give you as there is no magical figure to work towards.

What I can help with however is various differences that you will notice when working at varying temperatures and how that can help (or hinder) you.

This is quite a juicy topic so let's dig right in with Cold Process Soap Making first.

You will often read that you should soap at temperatures at between 80 and 120 fahrenheit. You will also read that the butters/oils and lye should be the same temperature or within 10 degrees of each other.  Not wrong but not the only answer either!

When I teach in my soap making workshops I always say to aim for a temperature of around 100f for both lye and oils and I explain that this is not the holy grail of temperatures as it were, but when you are learning you need a guide, a benchmark to work to. I also know it is a good temperature for beginners in general as there is no risk of a false trace and the batter won't thicken up as quickly as it would at a higher temperature and so they have a little more time to work with it.

However you will find some soap makers work with their lye at room temperature (this enables them to masterbatch the lye and saves time), to compensate they will generally have their oils at a higher temperature. If you have your oils  cool as well you will run the risk of a false trace ie your oils begin to set due to the temperature being lower than their melting point and you could mistake this for trace.

Other soap makers will use the heat transfer method. This involves using the hot, just made, lye solution to melt their butters and oils instead. ( This does not work for all recipes - if you have a high level of hard oils it will not stay hot enough long enough)

And other soap makers again like to soap at higher temperatures all round - ie 120 to 140f for both oils and lye solution.

None of these methods are incorrect. Just personal preferences.

What happens if my lye or oils are too hot or too cold?

There is not really a too hot or a too cold when it comes to soap making. It is more important to look at the individual recipe and then make a judgement.

If you are making an olive oil soap for example, you won't run the risk of a false trace if you soap at too cold a temperature as it won't set, you will find however that it may take forever to get to trace as generally the warmer the temperature the faster the trace. Conversely, coconut oil soap reaches trace quite quickly and lower temperatures will make it easier for you to control this. 

Working at a cooler temperature is really helpful if you are creating intricate swirls as your soap batter will stay fluid for longer and afford you more time to perfect your designs.

Drop swirls

When working with milk soaps you actively need your temperatures to be kept low to ensure your milk does not scorch, this is why we freeze our milk before mixing it with the sodium hydroxide.

Warmer temperatures will be a factor in helping to reduce soda ash and if you are making soap with bees wax you will have no option but to use hot oils. Beeswax melts at 145f, you need to ensure it does not set before it is mixed with the lye.

Warmer temperatures are also helpful if you are keen to ensure your soap gels throughout the whole loaf and wish to avoid the telltale ring that denotes a partial gel.

This is a very quick overview of situations whereby your recipe will impact on the temperature you aim for but it just helps to give you an understanding of the process and why there is no cut and dried rule regarding temperatures.

How can I avoid volcanoes in hot process soap making?

I just wanted to take this opportunity to cover this aspect of hot process soaping as I know volcanoes are the bane of many a hot process soap makers life. 

For those of you who do not hot process but are intrigued about what a volcano is in that context - imagine a saucepan of milk boiling over but that instead of milk it is hot soap! That is exactly what it is like - it can happen extremely quickly when your soap overheats and if you don't catch it soon enough there is not much you can do about it - except for watch it boil over!

Fortunately I have a pretty fool proof solution to share with you.

Melt your oils but ensure before adding your lye solution they are below 150f in temperature.

Mix your lye solution up in advance and allow it to room temperature. Ie 65 to 75F in most cases.

Cook your soap on low.

If you follow the above you will not get volcanoes. Guaranteed. I may regret saying that but I have always found it to be foolproof. 

I hope you have found that helpful. I would love to be able to give you a definitive guide but it is very much on the 'not that simple' list unfortunately.


Comments (5 Responses)

07 February, 2023

The Soap Coach

Inga , take a look at your recipe. If you are using oils that are high in stearic acid that will make the problem worse.

07 February, 2023


Hi! How do you achieve smooth soap without white spots( Stearic spots from what I’ve read) I really have so many questions lol

12 September, 2022


@Shana, you’re burning your hands with the lye most likely. Use gloves you silly goose.

08 August, 2022


I used Insta-Flo Lye in a recipe. I followed soap recipe. Now the batter seems to be burning my hands during clean up. I used teatree and lemongrass oils with EVOO, vit e, avocado oil, sunflower and coconut oils. What’s up?

20 October, 2021

Jan Lee-Buxton

Thank you so much for this, Keri. Despite having been a soaper for well over a year, I have always been confused when watching videos of other soapers making soap ‘at room temperature’. I tried it a couple of times, and just ended up with blobs of setting shea / cocoa butter! So nowadays, I always soap at close to 110 F, and try to work quickly when attempting swirls!

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