Guide — how to make natural homemade bar and liquid soap

Put simply, we combine all the ingredients in a particular order and blend the solution with an immersion blender until we reach a trace.

A trace means that when you stop blending and lift the blender out of the pot, the drips no longer dissolve into the liquid but cling to the surface and leave a trace behind. It can be a light trace, barely holding on the surface, or a heavy one, like a pudding.

You do not need to buy cold-pressed oils for soap making, because the high heat takes their benefits away anyway. Go ahead and buy the biggest and cheapest refined oils you can find in the supermarket. The only time I use a cold-pressed oil, extra virgin olive oil for instance, is when I want the soap to come out darker.

Second, for the longest shelf life, up to two years, buy oils that have a year or more left before their best-by date.

Third, I do not use palm oil or coconut oil, for vegan and environmental reasons, so every recipe here is without them. In general it is best to use the oils that are common where you live. I live in a Mediterranean area, so olive oil is my first choice, but if you are somewhere mangoes abound, use mango butter.

Most recipes call for more than two oils. The exception is olive oil, which can stand alone — that soap is called castile, and it is the example we will work through here.

Every oil brings something different to soap: lather, conditioning, or cleansing. Each also has a maximum percentage at which it belongs in a recipe. Olive oil can make up all one hundred per cent of the oil part, castor oil around five per cent, sunflower oil fifteen, and canola oil up to forty. One possible arrangement, then, is fifteen per cent sunflower oil, forty per cent canola oil, five per cent castor oil and forty five per cent olive oil.

• Avocado oil20 %
• Avocado butter12 %
• Argan oil10 %
• Canola oil15 – 40 %
• Carrot seed oil5 – 15 %
• Castor oil5 %
• Cocoa butter15 %
• Coffee butter6 %
• Coffee seed oil10 %
• Cucumber seed oil15 %
• Flaxseed oil5 %
• Grapeseed oil15 %
• Green tea seed oil6 %
• Hazelnut oil20 %
• Hemp seed oil15 %
• Oat oil5 – 15 %
• Olive oil100 %
• Macadamia oil10 %
• Pumpkin seed oil20 %
• Raspberry seed oil5 – 15 %
• Rosehip seed oil10 %
• Safflower oil20 %
• Sesame oil10 %
• Shea butter10 %
• Sunflower oil20 %
• Sweet almond oil20 %
• Walnut oil15 %

• Avocado oil — high levels of fatty acids make it good for regeneration, rich in vitamins A, B, D and E
• Argan oil — lathers well, rich in vitamins A and E, adds hardness to the soap
• Canola oil — a substitute for olive oil, gives a creamy lather
• Castor oil — absorbs easily into the skin, moisturises and builds lather
• Grapeseed oil — short shelf life, rich in antioxidants
• Olive oil — good for regeneration and hydration, does not lather and cleans poorly, gives a soft soap that takes longer to trace and longer to cure
• Macadamia oil — conditioning, stable lather
• Sesame oil — rich in antioxidants and fatty acids
• Sunflower oil — conditioning, rich in vitamin E
• Sweet almond oil — gentle on skin, medium lather, rich in vitamins A and E

I recommend distilled water. Tap water is safe if you boil it first and let it cool, but it may affect your batch:

• If you have hard water — and Zagreb does — minerals can cause orange spots on your soap, because some of the softer oils in the recipe oxidise. They can also affect the lather and the cleaning performance, and leave a white powder, soda ash, on top of the soap.
• Tap water contains the chemicals that make it drinkable, fluoride and chlorine, which can change the colour of your soap or make it go rancid faster.
• Tap water quality varies. If it works one time it might not the next, and given how much can go wrong with soap, it is hard to tell whether the water was the cause.

All of this only shows up after curing, so it becomes an expensive mistake if you have made several batches by then. Your chances are better with soft water or a filtering system. In that case I would advise citric acid in the recipe, which helps a great deal against scum and rancidity.

My advice is to find a shop where you can buy distilled water in bulk and fill your own bottles, so you avoid plastic. If you are going to use the same recipe all the time, make a small batch with tap water and see how it goes.

And if you do buy distilled water in plastic, get the bigger five litre bottles, and once one is empty use it for bio-enzyme.

The lye for bar soap is sodium hydroxide, also known as caustic soda. It is highly corrosive and harmful, so it is a fair question why anyone would want it in their soap.

The answer is the beauty of chemistry. Combined with water and oils, saponification occurs and the result is safe to use. The same happens when sodium is combined with chlorine, another toxic substance — we get the table salt we eat every day.

Before saponification, though, lye calls for caution: do not breathe it in, do not touch it with bare hands, and wear protective glasses, because it irritates the eyes. Which brings us straight to safety.

The easiest thing is to follow a recipe you have already found. Online calculators exist too, but I think it is essential to understand the relationship between the ingredients, so that you can check and work out a recipe yourself.

Always calculate the ingredients by weight, in grams. Oils have different densities, so measuring by volume is far too imprecise: a cup of olive oil is not the same as a cup of castor oil.

A recipe always begins with the oils: which ones we want, and how much. Each oil has a maximum recommended amount, which you have in the table above. The total amount of oil depends on how much your silicone mould holds. Mine fills to the top with about 1 kg / 35.2 oz of total ingredients, so I always use 900 g / 31.7 oz as the sum of my oils.

Here we are making the basic and best known castile soap, so olive oil alone, 900 g / 31.7 oz. Once the amount of oil is settled, the rest of the recipe falls into place on its own.

The lye is worked out with a simple formula. Every oil has its own saponification value (SAP) — the amount of lye needed to turn one gram of that oil into one gram of soap. SAP charts are available online, and these are the two I use:

• From Nature With Love — saponification chart
• Country Farm Lifestyles — saponification chart

The formula looks like this: oil amount × SAP value = the lye we need.

The SAP value of olive oil for bar soap (NaOH) is 0.135. For liquid soap, that is for KOH, the value is different.

In our case: 900 g × 0.135 = 121.5 g of lye. That is how much lye it takes to turn 900 g of olive oil into soap.

It is worth knowing that oils in a recipe cannot simply be swapped. You cannot say “I have no olive oil, I will just use sunflower” — you need the SAP value of that particular oil to know how much lye the recipe takes.

We now have the exact amount of lye for the exact amount of soap. Even so, we want a little more oil in the soap than lye, so that the soap is safe on skin. The next step, then, is to decide what percentage of the oil will not turn into soap.

There are two ways to do it: by adding extra oil at the end of the process, which is where the name superfat comes from, or by taking lye away while working out the recipe, which is where lye discount comes from. Since it is so easy to forget the extra oil at the end, I prefer the lye discount. It is also worth noting that essential oils and colourants added at the end count as superfat.

So this is the fourth thing a recipe rests on: oils, water, lye, and the lye discount percentage.

The discount runs between one and twenty per cent. The higher the percentage, the softer the soap and the more likely the oils are to go rancid. The lower it is, the harder the soap, the more drying on skin, and the more lather. Anything from five to ten per cent is generally best.

For our recipe we will use a five per cent discount, which means we use ninety five per cent of the lye: 0.95 × 121.5 = 115 g of lye.

It is worth noting that both we and the online calculators assume one hundred per cent pure sodium hydroxide, which is rare even when buying directly from a producer. So if we chose the minimum five per cent discount, it will really be closer to seven or eight, which is fine too. I mention this so you know that if you forget to work out the discount, it will not be zero; it will be around two or three per cent.

If the finished soap is too drying on your skin, use it for washing dishes. Dish and laundry soaps are usually made with zero superfat. I do not recommend soap in a washing machine or on clothes in general, but one batch will make no difference.

The amount of water is never exact, not even in the calculators. What we get is a range to choose from.

Water can be calculated from the amount of oil, the way many online calculators do it, or from the amount of lye, the way many soap makers do.

• From the oils — aim for thirty to thirty five per cent of the total oil weight. In our case 0.3 × 900 = 270 g of water.
• From the lye — the safest way is to take your lye amount and multiply it by three. In our case 115 × 3 = 345 g of water.
• Water discount — you can also make soap with less water. The trace then appears much faster, the soap cures in less time, and less soda ash builds up on top. Multiply the lye by two instead: 115 × 2 = 230 g of water.
• A simple single colour soap with olive oil — multiply the lye by 1.8 for an even smaller amount. In our case 207 g of water.

For an olive oil soap that lathers more, because it also contains castor oil, see the castile soap.

A liquid soap recipe uses potassium hydroxide (KOH) rather than sodium hydroxide (NaOH). On top of that, the same oil has a different SAP value: for olive oil with KOH it is 0.19, while with NaOH it is 0.135.

The procedure is the same as for bar soap. The difference begins when we start blending towards the trace. With NaOH the trace appears within a few minutes; with KOH it takes about an hour and a half: blend for a minute, leave it for ten, and repeat until the trace is there.

Once we reach the trace, the soap is cooked in a double boiler. We put the pot with the soap inside a bigger pot and fill the bigger pot with water up to the level of the soap. We cook it for one and a half to two hours, stir occasionally, and keep topping up the water in the big pot.

To check whether the soap is done, take a little on a spoon and taste it lightly with the tip of your tongue. If you feel something like a small electric shock or a sting, the soap is not ready. If you only taste something strange, it is done.

Once the soap is made there are two options:

• Store the larger part in a jar for later and dilute the smaller part with water.
• Dissolve all of the soap in hot water.

If you choose the second, leave the soap overnight in a large amount of water, and the next day stir it until it is completely liquid, topping up with more boiled water as needed. Store the finished liquid soap in a demijohn.

The full recipe is in the text on natural homemade liquid soap.

• While you wash the pots and the rest of the equipment, keep your clothes, goggles, mask and gloves on, because the lye is still present.
• You can wash the equipment in the sink. The lye that remains is not a problem — it is in fact often used in drain cleaning products. If you have the option, wash everything outside and dry it in the sun.
• Keep one sponge for this equipment only. I use a luffa sponge, but any sponge will do. I write about waste-free sponges in the text on six kitchen replacements.