Hot Process Soap Making

Hot Process Soap Making

This Wasn’t Quite the Post I Meant to Write.

I had a great post planned. With a whimsical introduction about being an urban, flat-dwelling mama yearning for the country, homestead, free range life. It was still about hot process soap making, but more hygge and lovely.

But, in the wake of Covid-19, I’ve decided to rewrite the intro before I post it. Hand washing is one of the best ways to limit the spread of Coronavirus, as well as flu and other ilnesses. Using soap and washing your hands for at least 20 seconds is an easy way to control the spread of the Covid-19. If you start running low on soap, it is surprisingly easy to make your own.

Keep it Simple

The particular recipe I share below is a little fancy, but you can make hot process soap at home with just standard olive or sunflower cooking oil. As long as you use a Lye Calculator (see explanation below), you can make a batch of soap with simple ingredients; essential oil, colourants and so forth are lovely extras but not needed. Always make sure saponification is complete (again, see below for explanation) before you use your soap, but otherwise, this is an enjoyable activity and good fun, but also perhaps more poignant now than I ever expected it to be.

Yours truly, in happy homesteading mode, before it all kicked off with this pandemic. Note the awesome safety goggles!

How is Soap Made?

There are several ways to make soap. The easiest is buying “melt and pour” soap, which is a pre-made soap base you can melt, add colour and fragrance to, then reset. But if you’d like to make it from scratch, the main ways are hot process and cold process. There’s also milled soap, but I won’t go into that here.

All soap making uses lye, which is sodium hydroxide AKA caustic soda, or potassium hydroxide. As the name indicates, it’s caustic! At pH 14, it can be quite dangerous if not used correctly, but by following a recipe and using safety equipment like goggles and gloves, you’ll be absolutely fine. It is probably best to keep young children and pets well out of the way, though. The lye part of melt and pour soap has been done for you, so if you’re extra nervous about it you can still try soap making!

The Science!

To make hard bars of soap, sodium hydroxide is mixed with oils and fats to cause a reaction called saponification, which breaks down and rearranges the various molecules to produce glycerol and, crucially, soap! You could also use potassium hydroxide, which would produce a much softer soap. Side note: this would be a great chemistry lesson for your teen homeschoolers!

Lots of mass produced soap has the glycerol removed (which they then add back into other products, like bubble bath), so your bars will feel more luxurious than most commercial soap!

You can vary your results by combining different oils and fats (which lend the soap different properties), colourants and fragrances, such as essential oils. There is also the option to add extras such as coffee grounds, oats or poppy seeds, for both appearance and extra exfoliation. Trust me, once you start down this rabbit hole, it’ll be hard to stop playing around with all the wonderful things you can make!

Getting started

The single most important thing to remember is this: your recipe must be correct so the final product is safe. You want to ensure the saponification reaction is complete, otherwise there will be free floating lye in your recipe, which could burn your skin.

Extras such as orange zest can add texture and interest to your soap (and smell incredible!)

The best way to do this is use a lye calculator , such as this one by Bramble Berry. You simply put in your recipe quantities of fat and oil and the calculator tells you precisely (I mean, REALLY precisely, grams to 2 decimal places precise!) the amount of lye and water to use. It is really important that you are as accurate as possible with soap making, which is why recipes are always in weight not volume. A digital scale is a must.

I’d recommend you aim for a 5% superfat recipe, which means there is 5% more fat than the amount of lye requires to be EXTRA sure the reaction is complete. Superfatting also gives you a more luxurious feeling bar at the end. The safest thing to do is use a recipe from book or blog until you’re sure what you’re doing. Feel free to use or adapt the recipe I share below!

Hot v Cold Process

Hot process “cooks” the soap from the outside in and cold process from the inside out. The method you choose matters in a couple of ways.

Feeling Hot, Hot, Hot…

Hot process AKA “crock pot” soap cooks more quickly, with less curing time needed for your finished bars. Some people use their bars literally the next day, but a week or so of curing is still recommended by pro soap makers, to be certain saponification is complete. You don’t have to be as precise about the lye and oil temperature during cooking, as it will all be heated together anyway.

An ordinary slow cooker is perfect for hot process soap making!

Often, the fragrance of hot process is stronger because of when the essential oil is added to the mixture, so you use less to make a nice scent (which is important because it is really expensive!). The downside (or upside, depending on your outlook!) is that hot process bars are much more rustic looking when finished, compared to cold process, as they are more solid when moulded.

Baby, It’s Cold Outside…

Cold process gives you a more professional looking finished bar. It is much easier to swirl different coloured batches together to make patterns (although this isn’t impossible with hot process, it is much more challenging). You have to be more accurate with temperatures than hot process, so the cooking is more involved, plus they take a bit longer to make. The scent is often much more subtle, or you need to use more essential oil to get a good fragrance. (Be aware there is guidance about the quantity of essential oil you can use in a skincare product to still be safe – it’s worth looking up if you design your own recipe).

The main downside is cold process bars have to cure for 4-6 weeks before they are ready to use. This means finding a place to store them in your house, regularly rotating them, and not getting to use them for a month and a half. This is also important if you’ve planned your soap as a gift but left it a little late!

But How Do I Choose?!

It’s really a personal preference which you’d like to go for. I went for hot process because I was concerned about space to cure them before use, but if I made soap again (which I DEFINITELY will!), I will use cold process and rearrange a bookshelf for curing. I’d rather have more control over the appearance of the end product and actually was a little sad that it took so little time to make as I was really enjoying the process!

That said, if for some reason I was nearly out of soap, I could whip up some hot process in a jiffy and it’s all good to go pretty darn quickly! It was still great fun to make and I highly recommend trying it!

What You Need (Equipment List)

There are a few essential items on your soap making kit list, but fortunately there are also corners you can cut to save money. You may even own most of the things you need already!

Not pictured: the rubber gloves and apron I’m wearing!

There is no need whatsoever to buy a fancy soap mould or cutter (though I did because I got carried away!). You can cut a long side off of an oat milk carton and use that, or line a Tupperware or takeout box with greaseproof paper (with some protruding so you can lift it out) and it will be just fine. You can slice your bars with an ordinary kitchen knife. Until you’re sure you want to continue this hobby, there’s no need to splash out. Truthfully, there are some pro soap makers out there who still use or prefer DIY moulds.

I’ve added some Amazon links to the following items for your convenience. On the off chance I become an affiliate in the future, here’s a friendly disclaimer: by clicking these links to purchase these items, I may make a small commission on the sale and there is absolutely no extra change to yourself! Thank you for supporting me, my family and this blog!

You will need:

An accurate digital scale. Ideally one that can display decimal places. As you are working with very strong chemicals, this is really your biggest must have.

A thermometer (for cold process). Either, a cooking one like this, which is also used for things like fudge making, or a digital temperature gun. If you can, go for the gun, as there is no cleaning needed if you want to measure your lye temperature, then the oils, then the lye again. Temperature is much less important in hot process, though you may still prefer to keep your lye and oils at a similar temperature before you combine them.

An apron, safety goggles and gloves (washing up gloves work well). Remember to also wear closed toe shoes, long sleeves and tie your hair back. This is to prevent the caustic lye solution splashing and burning you.

A heat proof jug for your lye solution. Polypropylene plastic (PP) is a great choice. Some soap makers suggest glass or pyrex, too. Just be careful, as micro abrasions can happen over time which can weaken them and cause cracks or breaks.

An immersion blender (stick blender). Without this bit of kit, the entire soap making process will take AGES, especially if you are doing cold process, so it really is a must! A stainless steel ended one is ideal, but I just have an ordinary plastic ended one and it works fine. Stainless steel is just much easier to clean!

A stainless steel pot for the oils (cold process) or a slow cooker/crock pot (hot process). Note: soap can grow as it cooks, so make sure your crock pot is a large enough capacity for your batch (it shouldn’t be more than half full when you add the lye to the oils and fats).

A small container to measure the lye crystals into initially.

A saucepan to melt solid fats and oils (cold process only).

A sillicone spatula.

Stainless steel whisk.

A stainless steel spoon, for stiring the lye. Avoid other metals, as they can be reactive.

Small containers for measuring out essential oils, botanicals, other additives such as oats or seeds, extra oil for superfatting, powdered colourants etc. Could be plastic, glass, pyrex, ceramic or stainless steel.

Measuring spoons (for adding botanicals etc). If you are working with colourants such as mica powder, you may need to measure tiny amounts such as 1/16 tsp. These spoons have a 1/16 included, or you could just approximate with your usual spoons (colouring doesn’t need to be precise, though tiny amounts usually go a wrong way). (The recipe below is not coloured, an ordinary teaspoon is fine to add your zest).

For recipes that use citrus zest (like this one!) you will also need a zester or potato peeler and sharp knife. If you use the peeler method, press lightly to avoid getting too much white pith. (Honestly, I’m tempted to add zest to every soap I ever make, it smells so good!).

OPTIONAL: A fancy soap mould and cutter. This cutter link is for a crinkle cutter, which is pretty cool! You can also get individual moulds, if you prefer. Rounded ones are also available.

The Recipe!

I looked at several blogs to get a feel for how much total fat and oil would be good for a batch. Generally, a 1 pound recipe (454g) yields around 5-6 standard size bars or up to 18 mini bars. The 1 pound recipe I adapted used 500g oils and fats to create 11-12 small bars, around 50-60g each when first cut. The weight will drop as the bars dry and harden. I made smaller bars on purpose, to lower the curing and drying time. If you buy the mould I linked above, the batch fills it around half full and I cut my bars 2cm wide.

If you want to experiment lots with flavour and colour, small batches are a good idea, as you’ll use less of each ingredient so have more left for different bars. This also means that if you have a disastrous batch, you haven’t ruined all of your ingredients at once!

St. Clement’s Soap (Orange and Lemon) Ingredients

I used up some old mandarin oil that came with our cloth baby wipes instead of opening my new orange oil – it worked just fine!

You will need:

  • 70.32g lye
  • 157.26g water
  • 150g olive pomace oil
  • 150g coconut oil
  • 75g sweet almond oil
  • 75g cocoa butter
  • 50g castor oil
  • 2tsp orange essential oil
  • 2tsp lemon essential oil
  • 1/2 tsp cedarwood essential oil
  • 1-2tsp finely chopped orange zest (optional, but beautiful!)

Method (hot process)

Make sure you are wearing your safety goggles, gloves and apron before you begin. Start by pre-measuring all of your ingredients, so they are easy to add at the right moment! Make sure your mould is ready to go and your slow cooker is on low.

  1. Add your coconut oil and cocoa butter to the slow cooker to melt – use the LOW temperature setting throughout this recipe.
  2. Meanwhile, add your lye to the water in a jug and stir with a stainless steel spoon. NEVER add water to lye, ALWAYS add lye to water. You could cause a volcanic effect if you do this the wrong way around so be extra cautious! Make sure you mix your lye in a well ventilated space (indoors is fine, but right by a wide open window is best).
  3. Once the fats are melted, add your liquid oils to the slow cooker and swirl together.
  4. Add the lye solution to the slow cooker.
  5. Using the stick blender, swirl the mixture together (without turning the blender on at first – use it like a spoon).#
When you first add the lye, it sinks beneath the oil
  1. Occasionally, bring the blender to the middle of the slow cooker and give it a pulse for a second or two. Then resume stiring with it off. Then come back and pulse.
  2. Keep up stiring then pulsing until you reach “trace”. This means your soap mixture has the consistency of a thin-medium custard or pudding. If you drip a line of the mixture on top of itself it leaves a “trace” and the line is visible.
This is a (slightly thick!) trace. In cold process, I’d want to mould up a smidge before it’s this thick, but in hot process it doesn’t matter at all if it goes a bit too far
  1. Once you reach trace, you can cook your soap! Place the lid on the slow cooker and leave it on a low setting for around 50 minutes.
  2. Periodically check back on your soap. It can grow as it cooks, so if it looks like it may overflow or is getting too large, remove the lid and stir with a stainless steel spoon until it settles again. Then place the lid back on to continue cooking.
  3. Once 50 minutes have elapsed, it is very likely that the soap is ready. Some soap makers test if it ready by taking a tiny amount, rolling it into a ball and licking it – if it feels like it “zaps” your tongue strongly, it’s not quite done! If it tastes soapy, it is done. Note: lick your soap at your own risk!
  4. As soon you think the soap is ready, quickly remove the lid and stir in the essential oils and half of the orange zest. It will quickly begin to set, so rapidly transfer the mixture into your mould, flattening the mixture with the silicone spatula. Tap the mould against the worktop to help remove air bubbles.
  5. Sprinkle the remaining zest over the top of the soap to decorate the top while it is still hot and wet (otherwise it won’t stick!)
  6. Set the mould aside for 12-24 hours for the soap to harden.
  7. Once the soap is hard, it can be removed from the mould and sliced. You can slice it into any size you like! If you used individual silicone moulds, pop the soaps out.
  8. Leave the separate bars to dry and harden, periodically turning them so that all sides are exposed to the air. A bookshelf is a good place to keep them. One way to be certain that your soap is ready is to weigh the bars when they are cut, then again every day or two. When they stop losing weight, they have lost all of their excess water and can be stored in an air tight container.
  9. Lather up and enjoy!

What next?

If I made my batch again, I would replace 1tsp of the lemon essential oil with may chang essential oil. This helps the citrus scent to stay strong. My batch is still lovely but definitely more subtle now; citrus is apparently notorious for the scent fading, which I didn’t know at the time!

I hope you enjoy having a go at your own hot process soap making! Let me know in the comments how you get on, or tag me in your instagram posts @the.everyday.adventurers so I can see your awesome creations!

Have fun and happy homesteading!

Jen xXx



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