Solid bar soap is made by mixing an acid (plant or animal fat) with an alkali (a lye solution that’s made with sodium hydroxide and water) to form a chemical reaction called saponification.

Once saponification has occured, additional ingredients such as scent, colour and texture can be added. The mixture is then poured into a mould and left to set, before being cut to size (if applicable) and curing. Once cured soap is then ready to use and enjoy. 

 


REQUIRED INGREDIENTS

Alkali

The alkali used to make solid bar soap is sodium hydroxide (potassium hydroxide is used to make liquid soap). Sodium hydroxide (which is often sold in a solid crystal form) is mixed with water to create a solution called lye

Be sure to use 100% sodium hydroxide or ensure it states the product you’re buying is suitable for soap making.

Water

The amount of water used to create the lye solution is subjective. The minimum amount of water needed to form a solution is the same quantity (by weight) as sodium hydroxide, however, using this amount of water creates a risk of lye crystals not fully dissolving and saponification happening very quickly. Adding more water is safer and makes the process easier. 

The more water you use the runnier the soap will be when you pour it into the mould and, in some cases, will slow down how fast the chemical reaction of saponification occurs. Any excess water will be evaporated out of soap during the curing phase. 

Use distilled or demineralised water. I get mine from a supplier that allows me to refill my empty 5 litre container when required.  

Fat

Many different fats, or combinations of fats, can be used to make soap – both from animal and plant sources. 

I personally only use plant based fats, such as oils and butters, and have no experience with using animal fats. I don’t, and never will, use palm oil, which is a very common soap ingredient.

The quality of the fat does not have to be high for soap making, for example, it’s fine to use the refined versions of oils and butters such as coconut, olive, shea, olive etc.

Saponification Value

Each fat has a specific saponification value (SAP Value), which is the amount of sodium hydroxide needed to saponify the fat used in a recipe.

You cannot exchange the type or quantity of a fat within a recipe as doing so would require a new calculation for how much sodium hydroxide is needed. This is very important, because if you use too much lye (aka caustic soda) in a recipe and it doesn’t all get saponified by the fat, it can leave your soap caustic, which can lead to burining the skin.

The easiest way to determine the amount of sodium hydroxide needed to saponify the chosen fat within a recipe is to use an online soap calculator. There are a number available, with my prefered one being www.soapcalc.net

Superfatting / Lye Discounting

To ensure all lye is reacted, an extra percentage of oil is used to superfat soap, this helps to ensure there is no unreacted lye left in the soap and helps to condition the skin. Superfatting soap by 5-8% is the norm, however there are some exceptions to this rule, especially when making pure coconut oil soap, which is extra superfatted to counteract this superier cleansing effect.

 


ADDITIONAL INGREDIENTS

Natural Scent

You can scent soap by using essential oils, but keep in mind you need quite a lot for it to be effective. Some essential oils are better to use for soap making than others due to safety and scent retainment. 

I personally use, and have had good results with, lavender and eucalyptus essential oils. 

As a general rule, I believe it’s safe to use up to 4% eg 40ml per 1000g, but generally use a 2% ratio. It’s important to do research to ensure the essential oil you want to use is safe for soap making.

Natural Colour & Texture

I like to use dried used coffee grounds to add colour and texture to my body soaps. We use a coffee plunger at home and I simply tip out the used contents onto a plate and leave out to dehydrate and then store in a jar for future soap making use. 

You can also use clays, dried herbs and spices, however I have not personally had much experience in using them yet. I have used pink and green clay with great results. Some colours can change with curing.

My rule of thumb is to use 1 teaspoon of colourant, such as clay, per 500 grams of fat and up up to 1 tablespoon of coffee grounds per 500 grams of fat. 

 


EQUIPMENT

Safety Gear

  • Googles to protect your eyes
  • Rubber gloves
  • Long sleeve top, trousers, enclosed shoes
  • Face mask/cover (to avoid lye fumes – optional) – I use a wide large headband that I pull over my nose and mouth and keep my head away from the fumes
  • Vinegar for neutralising lye if there’s a spill

General Equipment

  • Digital scale
  • Stick blender
  • Heating element to melt solid fats if applicable (eg stove top) 
  • Cutting board and cutter
  • Drying rack
  • Thermometer
  • pH test strips (optional)

Soap Making Equipment

I recommend using stainless steel mixing bowls and utensils. However you can also use enamel (with no chips), heat resistant glass, number 5 Polypropylene plastic. Don’t use: aluminium, tin, copper as they can react with the lye.

  • Slops bucket (aka wash bucket) to put used equipment into
  • High sided container to weigh oil into (and mix soap)
  • Utensil to remove solid oil/butter from storage container (if applicable)
  • Container to weigh sodium hydroxide into 
  • Utensil to remove sodium hydroxide from the storage container
  • Container to weigh water into (and then mix sodium hydroxide into, which get very hot when reaction occurs)
  • Long handled utensil for mixing lye solution (lye = sodium hydroxide and water solution)
  • Utensil for colour or texture addatives (if using)
  • Utensil for measuring essential oil (if using)
  • Utensil for spooning out soap into mould (if applicable)
  • Spatula for removing mixed soap from container and edges
  • Soap mould

Moulds

You can use just about anything that holds a shape for soap making – including milk cartons. My personal favourite is using silicon moulds as they don’t require any lining and are easy to remove soap from. I recommend using a loaf shape mould for beginner soap making.

Depending on the mould you use you may have to line the mould with baking paper or reusable silicone sheet so you can remove it when set. 

You can use the following formula to determine how much soap a mould will hold: Length x Width x Height = soap amount in grams.

 


RECIPES I USE

Bar Soap Goals

  • Hard bar of soap
  • Palm oil free
  • Simple ingredients
  • Natural Additives
  • I don’t care if it looks pretty – I just want it to work well

Laundry and Dish Soap

This 1% Superfatted Coconut Oil Soap is designed to be an efficient cleaner without any additional fat, other than a little bit to ensure all the lye has been used up in the recipe for safe use. I don’t add any colour and often no scent either. 

  • 500g Refined Coconut Oil (24C/76F)
  • 190g Distilled or Demineralised Water
  • 73g Sodium Hydroxide
  • 15g Essential Oil (optional)

Hand Soap

This 20% Superfatted Coconut Oil Soap is versatile enough to be used for hands and body, although my personal preference is to use it as a hand soap. It produces an extremely solid bar of soap which is very cleansing, making it great for dirty hands and bodies. It can be used effectively in hard water and is a great marine soap, producing a good lather. Some people with sensitive skin can find 100% coconut oil soap too cleansning and drying, in which case I would swap this recipe for the one below. 

I always add a colour or texture so this soap is distinguishable from the Laundry and Dish Soap. 

  • 500g Refined Coconut Oil (24C/76F)
  • 190g Distilled or Demineralised Water
  • 73.3g Sodium Hydroxide
  • 15g Essential Oil (optional) – my favourite is Eucalyptus Lemon Oil (INCI: Eucalyptus citriodora)
  • 1 tablespoon used coffee grounds (optional)

Body and Hair Soap

I’m still in the process of formulating and testing hair and body soaps to see which one I like best. I want something that’s a little more nourishing than pure coconut oil soap. 

Here’s my current favourite: 

Coconut, Olive and Shea Soap 8% Superfatted

  • 250g Refined Coconut Oil (24C/76F)
  • 125g Olive Oil
  • 125g Shea Butter
  • 190g Distilled or Demineralised Water
  • 72.4g Sodium Hydroxide
  • 15g Essential Oil (optional) – my favourites are Lavender or Rosemary
  • 1 teaspoon coloured clay

 


METHODOLOGY

There are a few methods of making bar soap: 

  • Cold Process
  • Hot Process
  • CPOP
  1. Set up your work station, including pre-prepared moulds, so everything is laid out and easily accessible 
  2. Put on safety gear
  3. Weigh out your oils/butters and use low heat until just melted (if necessary)
  4. Weigh out sodium hydroxide and set aside
  5. Add the sodium hydroxide to the water in a ventilated area (ALWAYS ADD LYE TO WATER – not the other way round) and mix to combine. This produces a chemical reaction that produces fumes and heat. Avoid breathing the fumes. Let the mixture stand (mixing occasionally) until it becomes clear and cools to ~ 40C (or lower than the flash point of your essential oil, if using). Ensure all sodium hydroxide crystals are dissolved before using.
  6. Add your mixer (stick blender – not turned on) into the middle of container with oil/s and pour the lye mixture into the oil using the mixer to guide the lye solution into the oil. 
  7. Mix briefly to combine while mixer is still turned off. 
  8. Turn on blender to mix, ensuring it stays below the solution to avoid splashing and incorporating air, and blend using a figure 8 motion until you reach a light trace (this is when the fat and lye are saponified). Light trace is when the mixture starts to thicken and leaves a trace when you take the turned off blender out of the mixture. You can use a spatula to scrape the edges and ensure all oil and lye are combined. 
  9. While your blender is off, add any additional ingredients, such as coffee grounds or essential oils and stir briefly (with turned off blender) to combine. 
  10. Turn on blender to incorporate additional ingredients. 
  11. Pour or scoop mixture into moulds and store somewhere safe while it sets. Safe = away from animals/humans – make sure it can not be knocked over or mistaken for food. An esky or cupboard can be suitable places.

Note: Essential oils are added at trace so they don’t react (saponify) with the lye, they can effectively be treated as superfatting the soap.

Cold Process 

Hot Process

CPOP

 


CLEANING UP

As you’re making your soap, continue to add used items to your wash bucket. 

If you want to wash up straight away: Once you’ve poured your soap into the moulds you can attend to the ‘dishes’. Rinse your gloves if you have any soap on them. Keep your gloves on and add some vinegar to the wash bucket – concentrating particularly where the lye, lye solution and left over soap mixture are. Fill the wash bucket with warm/hot water and leave to soak for a few minutes. Empty the water and continue to wash equipment with your gloves on. 

OR let soap set and then wash up (my preferred method): After making soap, simply leave the used equipment to sit for a day or two and wash the set soap off the equipment. Use gloves. Soak and rinse equipment before washing. 

IF you intend to use the equipment for food preparation after making soap then it’s recommended to wash equipment a second time. I personally keep my soap making gear exclusively for soap, but some people don’t worry. You’ll have to do your own research and use your own intuition to know what’s right for you. Some people oppose using soap making gear for food preparation.

 


CURING AND USE

After you pour your soap into your moulds it will continue to heat up for a while. Leave it for 12-24 hours to fully set (like a solid block of cheese) – there should be no heat coming from it. 

Use gloves when you take it out of the mould as a precautionary measure. Remove soap from the mould and cut it before placing it on a drying rack to cure. If you use small individual silicon moulds, you can remove and place straight on the drying rack. 

Leave your soap to cure for 2+ weeks to allow excess water to evaporate, which makes the soap more solid and hard. This prevents soggy soap and also ensures it’s safe to use with no unreacted lye solution. 

I personally check my soaps pH before using by adding a little distilled water onto the soaps surface, agitating and then testing with a pH strip. My soap has always had a pH of around 9. I wouldn’t use a soap with a pH higher than 10, I’d keep it to rebatch (once I know how), or allow it to cure for longer and re-test. 

You can also periodically weigh your curing soaps to determine when they stop changing weight (evaporating water).

I’ve found the scent of my soaps fade and evaporate over time, which is why I’ll use a high amount of essential oils if it’s a soap I know I’ll be keeping for a while and want to continue to smell nice. 

You can wrap soaps in paper offcuts or material to help maintain the scent. It’s important to ensure all water has evaporated before wrapping, otherwise mould can form.

When using bar soap you want to allow it dry between uses so it doesn’t sit in a pool of water. Use a soap dish, hang from a rope or place soap inside a vegetable bag (like an onion bag) and hang. 

I like to keep soap slithers in my car and bag for when I may need soap while I’m out. You can simply shave soap slithers off your bar soap with a vegetable peeler and store in a container. 

 


NOTES, EXPERIMENTS AND OBSERVATIONS

 

 


REFERENCES AND RESOURCES

pH Reference

  • Sodium Hydroxide = pH 13-14
  • Coconut Oil = ~pH 6 (from my personal test)
  • Soap = pH 8-10
  • Distilled White Vinegar = ~pH 2.4
  • Our skin’s acid mantle = ~pH 5.5

Where I buy my soap making ingredients

  • Demineralised water (5 litre refillable container) = Big Bubble in Midvale Western Australia
  • Refined coconut oil (5 litre container) = Range Products in Welshpool Western Australia
  • Sodium hydroxide (2kg caustic soda) = Range Products in Welshpool Western Australia
  • Essential oils for soap = Range Products in Welshpool Western Australia
  • Coloured clays = Range Products in Welshpool Western Australia
  • www.rangeproducts.com.au
  • bigbubblemidland.com.au 

Books I like

Look in your Local Library for good soap making books. I always choose books that use natural scent, colours and textures. 

  • Aromatherapy Soap Making by Elizabeth M Wright. 2nd Edition. How to make your own luxury aromatherapy soaps
  • Smart Soapmaking by Anne L Watson. The simple guide to making soap quickly, safely and reliably OR how to make luxurious soaps for family, friends and yourself. Version 1.2
  • Scientific Soapmaking by Kevin M Dunn. The chemistry of the cold process. Revision 1.67
  • Handmade Soap Book by Melinda Cross. Easy soapmaking with natural ingredients. Updated second edition. (I got this from my local library)

Websites

Soap Calculators

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