How To Hot-process Soap

Written by Sally_in_Wales

A good way to make soap for Christmas gifts if you've left it to the last minute

Soap making from scratch can be very rewarding, allowing you to create household cleansers or bath soaps where you know exactly what the ingredients are. It can also be a little bit frustrating when you have to wait for the batch to cure for at least a fortnight before trying your latest recipe.

Hot processing soap allows you to speed up the process, a batch of soap can be ready to unmould within three or four hours of starting and can be used as little as 24 hours after making. Historically, its how soap was processed right up until relatively recently, and its a good next step if you are already making your own cold process soap.

(Confession- These photos do not show me wearing gloves, you should take exactly the same safety precautions when making hot process soap as you do cold process!)

This article covers the method, not recipes. Any basic soap recipe will work this way, I'm demonstrating it using the same Olive Oil Castile recipe in the beginners soapmaking article . Hot process soapmaking is not an exact science, many factors affect the speed and appearance of the reaction, but this article should give you an idea of what to expect.

Start by weighing your oils into a stainless steel pan. Try to choose a fairly big one, this pan really could have done with being a bit bigger.

Add your lye in the usual manner, and stir or whizz with a stick blender until you get light trace:

Keeping the heat extremely low, stir steadily until the soap thickens. Sometimes you'll find it starts to split out first, thats ok, just keep stirring until it all comes together and goes thick:

Now you can stir it every 5 minutes or so until it starts going into its gel phase. (I'd stay in the kitchen if I were you, different recipes get to this stage at different rates and the soap often expands at the same time) You might find this stage takes about 10 or 15 minutes to reach:

Once it starts to gel, stir fairly frequently until all the soap has loosened up and become darkly transparent. This is often likened to applesauce, though its a bit stiffer in my opinion:

Stir every couple of minutes now, and be aware that steam in the soap can make huge bubbles rise up and burst. You are aiming to get beyond that dark transparent fairly fluid stage to a point where its extremely thick but fairly fluffy in texture. Its often likened to mashed potato, but its much harder to get a spoon through. Aim to get every last scrap stirred well in, what you are doing is speeding up the chemical reaction so that the gel phase completes very fast, and a lot of water is driven off as steam.

When it all seems even and the soap is drying to the bottom of the pan when you stir down that far, either glop it into a mould (it won't easily pour) if you want a plain soap, or take it off the heat and stir in scents, fillers etc. You may find you need less essential oil than in cold process because a lot of smell is lost in cp during the chemical reaction as the soap gets so hot for a prolonged time during gel phase. We've gone past that point, so the soap is more stable and won't distort smells as much, but it is still red hot, so be careful. Smooth the top of the moulded soap down through a piece of waxed paper or clingfilm, and leave to go cold:

Its normal for the soap to stay fairly molten in the mould for an hour or so, then it will set. Once its cold you can unmould and cut it straight away. Its technically useable straight away, but for best results wrap it loosely in a piece of tissue paper or something that breathes but keeps the dust off, and it will air and lose more moisture over a day or so.

In texture hot processed soap is usually a little creamier and softer than cold process, its rare to get that brittleness that cp sometimes develops.

Add a bit of water to the soap pan and use the residual heat of the stove to melt down the pan scrapings and you'll have a small amount of liquid soap that typically does a couple of loads of laundry or a few batches of dishes.

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