The "Cold saponification" Info Sheet

Soap is the product of a chemical reaction between a fat (plant oil, plant-based butter, animal fat, etc.) and a strong base (soda or potash).

Soda ash (sodium hydroxide) is used to make solid soap. Potash (potassium hydroxide) is used to produce pasty or liquid soaps (black soap, liquid Marseille soap). We will only be talking here about the production of solid soap using sodium hydroxide.

Oils and butters are mainly made up of fatty acid triglycerides. When sodium hydroxide is added, these are transformed into soap according to the reaction below (R represents the carbon chain of the fatty acid, a long chain of 12 to 22 carbon atoms for the fatty acids most commonly found in plant oils).

Gentle soaps rich in active ingredients!

Soaps made by cold saponification are naturally rich in glycerine, produced during the saponification reaction. It provides the soap with softness and moisturising properties.

In addition to fatty acid triglycerides, plant oils and butters contain an unsaponifiable fraction, i.e. compounds that will not react with the lye. These include phytosterols, tocopherols (vitamin E), carotenoids (vitamin A), terpenes, squalene, squalane and fatty alcohols.

These substances have highly beneficial effects on the skin, including antioxidant, nourishing, emollient, softening and protective effects… A homemade soap, made by cold saponification, will naturally contain the unsaponifiable portion of the oils and butters used, giving it unique properties.

The manufacturing process for industrial soaps, on the other hand, will often have denatured or even eliminated the unsaponifiable fraction.

Superfatting rate: what is it?

The superfatting rate is the percentage (of the total weight of oils) that remains unsaponified in the finished soap. The soap is then "superfatted". In cold saponification, it is essential to superfat soaps. There are 2 ways of superfatting soap:

1. Soda reduction

2. Additional superfatting at the "trace" stage

1. Soda reduction

This means using less soda than is theoretically necessary to saponify all the oils in the mixture. In this way, all the soda will be consumed by the saponification process and a portion of unsaponified oils will remain in the soap. This means that the theoretical amount of soda is reduced by the % chosen.

The soda reduction is essential as a safety margin, because the saponification indices used to calculate the amount of soda to add are averages and may vary. We recommend that you always choose a soda reduction of at least 5% to be on the safe side.

A reduction of more than 5% means that the soap is "superfatted" and therefore softer. This is because a little of each oil/butter from your initial oily mixture will remain in the soap, and these unsaponified oils will contribute their properties to the skin. For this reason, the reduction in soda is sometimes called the "superfatting rate".

2. Additional superfatting at the "trace" point

Another way of superfatting soap is to add plant oil (or melted plant-based butter) at the 'trace' stage, i.e. at the end of the preparation process. Most (if not all) of this oil will remain unsaponified. This is particularly useful with expensive, temperature-sensitive oils, or oils and butters whose properties you want to take particular advantage of.

Adding oil at the end of the preparation process is also very useful for pre-dispersing other ingredients you wish to add (colourings, essential oils). This will make it easier to distribute them evenly throughout the soap paste.

3. Which superfat should I choose?

Total superfatting rate (%) = "Soda reduction (%) + Additional superfatting (%)".

For a very mild soap, we recommend a total fat content of between 8% and 10%. It is possible to go higher (to 12% or even 15%, for example), but be aware that a soap that is very "superfat" is likely to be soft. It may also be more susceptible to rancidity, especially if the oils used for super-fatting are sensitive to oxidation. In some cases, a soap that is "too superfat" may also ooze oil. In extreme cases, a soap that is too rich in oil may go out of phase during manufacture.

We strongly recommend that you combine a reduction in soda (of at least 5%) with additional "trace" superfat.

Several options are available:

• Soda reduction of 5% as a safety margin and additional superfatting with a particular oil or butter of 3 to 7%.

• Soda reduction of between 6 and 10% for superfatting in all the base oils and additional superfatting (2-3%) in a particular oil or butter at the "trace" stage.

• Soda reduction of between 5 and 12% for a soap that is simply fatted with all the oils in the mixture if you don't want to add any particular oil.

• Soda reduction of 1 to 4%, and in this case IMPERATIVELY superfatting so that you have AT LEAST 5% (at least 8% is recommended for a mild soap) of total superfatting**(not a recommended option** as there is always the risk of forgetting to add oils at the end of the preparation, or of having a mixture too thick too quickly to guarantee a homogeneous mixture of the oils added).

4. How to use

We've provided a calculator to help you work out how much soda to use. You can choose the "soda reduction" and "additional greasing" you want, taking into account our recommendations:

• Enter all the oils in your base mix into the calculator. The calculator provides a results sheet, which will include a table showing the quantities of soda calculated with "reductions" from 1 to 12%.

• Additional lubricating oils should not be entered in the calculator table when calculating the soda ash. However, you can enter the desired percentage of additional fat in the box provided. The results sheet will give you the weight of oil (or melted butter) in grams, to be added at the time of the "trace" to obtain this percentage of additional fat.

5. Focus on... Saponification temperature

We recommend that you make your melted oils/soda solution mixture at a temperature of between 35 and 50°C, or even up to 55°C in some cases. Choose a higher temperature (45-55°C) in the following cases:

• if your formula is rich in 'hard' fats (butters, solid oils), to avoid the mixture setting too quickly

• If you use wax in your formula, we recommend saponification at around 55°C.

• if your formula is for a small volume (100 ml moulds), as these formulas will have less of a tendency to rise in temperature in the mould.

A high temperature (45-55°C) will accelerate the saponification process, and therefore generally favour a quick trace. On the other hand, too high a temperature (over 60°C) can break the emulsion (which takes on a "curdled" appearance). Choose a low temperature (35 to 40°C) instead in the following cases, if the formula allows:

• if you are using additives that accelerate the "trace", such as honey, certain essential oils or fragrances to make marbling that require a paste that remains fairly fluid for some time.

A short guide to oils used in saponification

In theory, it is possible to saponify all types of fats (plant oils, plant-based butters, animal fats), but the choice of oils will greatly influence the appearance and properties of the soap: hardness, foaming power, softness on the skin, etc.

Depending on their chemical structure (saturated or unsaturated, and the length of the carbon chain: C12, C14, etc., depending on the number of carbon atoms), fatty acids will contribute different properties to the soap. The table below gives a generic guide to the properties of the main fatty acids found in plant oils and butters.

The fatty acids that add hardness to soap are mainly saturated fatty acids, naturally present in high proportions in plant-based butters or 'solid' oils. The presence of a sufficient quantity (30 to 60%) of this type of oil in your soap will guarantee good hardness. You can also add stearic acid to your recipe to harden your soap.

The most detergent fatty acids are those with a short chain. The fatty acid that will provide the most effective washing power, as well as a beautiful, abundant lather, is lauric acid (C12: chain with 12 carbon atoms), present in large quantities in Copra, Coconut and Babassu oils. These oils are therefore very useful in the composition of your soaps, but it is often advisable not to use more than 30% of them, unless you want a very detergent soap. A proportion of 15-30% of this type of oil is ideal.

Unsaturated fatty acids (oleic, linoleic, linolenic) are of interest in saponification for their nourishing and skin-softening properties. You'll find them in most liquid plant oils: Olive, Apricot Kernel, Macadamia, Sweet Almond, Avocado, Hemp, etc.

Once you've tested several recipes and learned to see the effect of the different oils on the finished soap, you can experiment with more original recipes, but to get started, we recommend you follow these guidelines for your mixtures.

For a well-balanced soap formula, we recommend that you use the following in your mixture of oils for saponification:

• 20 to 30% Coconut, Coprah or Babassu oil, to provide good foaming power and a good washing effect (all soaps can lather and wash, even without these oils, but their richness in lauric acid promotes abundant lathering and increases washing power).

• 40 to 60% "hard" fats (butters, palm oils, etc.), including the percentage of coconut, copra or babassu oil, which are "hard" fats. This will add hardness to the soap and make it last longer. In general, if you use an average of 50% 'hard' fats, the formula will have satisfactory hardness.

• The rest of the base can be made up of liquid plant oils, which add softness and properties for the skin.

Special mention should be made of Castor oil, which is rather unusual but particularly interesting for saponification. Due to its high ricinoleic acid content, it produces a very creamy, stable lather when combined with a 'foaming' oil rich in lauric acid. It also makes the soap very mild. It is best used at a level of 5-15% in the oil mixture. If too much is used, it will tend to produce soft soaps.

Olive oil, although mainly composed of unsaturated fatty acids (especially oleic acid), produces very hard soaps when used in high doses (>60%). It is even possible to make very satisfying 100% olive soaps, appreciated for their great mildness.

Jojoba oil is actually a liquid wax because it is made up of fatty acid esters rather than fatty acid triglycerides. Its saponification therefore does not produce glycerine. It has little foaming power and little washing effect, but its long-chain fatty acids are softening and it has the advantage of being stable to oxidation. It can be used in cold saponification, as long as low doses (10%) are used.

Prepare a caustic soda solution

To begin with, it's easiest to use caustic soda in liquid form, in solution (preferably at a concentration of around 30%).

If you use caustic soda in solid form, it will need to be dissolved in water for saponification. The calculator will give you a range of acceptable quantities of water. To start with, take the average of the range or a value in the upper half of the range.

Prepare your soda solution in a Pyrex or heat-resistant plastic container.

Place your container with the required quantity of cold water on a stable surface, preferably in a well-ventilated place, or in your kitchen sink for example.

Weigh out precisely the amount of soda in another container, then add the soda to the water (not the other way round), stirring gently with a large plastic or stainless steel spoon. This will heat up and produce fumes. Do not breathe in the fumes.

Move away, leaving the container in place. Stir from time to time and wait for the soda to dissolve completely and for the solution to cool to around 35-50°C before using.

Warning

Be careful not to confuse caustic soda (sodium hydroxide) with soda crystals (sodium carbonate) or sodium bicarbonate, which cannot be used in saponification. Beware, too, of 'unblocker' products that are soda-based but contain other ingredients. Read labels carefully, and if in doubt, ask your retailer.

Soda is an extremely caustic product (highly corrosive, causes serious burns) that should be handled with the utmost care.

Please note

Note that at the end of the saponification process, after the cure period, all the caustic soda will have reacted with the oils to produce the soap. The finished soap no longer contains any caustic soda.

What is caustic soda?

Caustic soda or Sodium hydroxide is the reagent that transforms oils into soap. You can buy caustic soda in DIY shops or drugstores to make your soaps. It can be in solid form (pure), or diluted in water (lye). In the case of the latter, the concentration of the solution must be indicated on the bottle, so choose between 30 and 35% .

To begin with, we recommend using a commercial soda solution (soda lye at around 30%).

Precautions for using caustic soda

• Store caustic soda with hazardous products, out of the reach of children and separately from acids.

• Prepare your environment well: remove all clutter and keep children and pets away...

• Protect yourself : long, thick gloves, safety goggles, closed shoes, "safe" clothes with long sleeves and legs covered and, if possible, an apron or smock.

• Use resistant materials: Pyrex, glass, silicone, heat-resistant plastic, stainless steel (avoid other metals), etc.

• For better control of your movements, do your work standing up.

• When saponifying, always pour the soda solution into the oil mixture, not the other way round.

• Beware of caustic soap paste splashes. Choose a suitably sized container and keep your mixer at the bottom of the mixture.

• If any soda or soap paste is splashed onto the surface, rinse immediately with plenty of water.

• Soap paste is still caustic when poured into moulds. Keep your gloves on and your filled moulds out of the reach of children.

• Wear gloves again when unmoulding your soaps as they may still be caustic.

• Also wear gloves when cleaning your containers and utensils. Do not throw soap paste down the sink: wipe up the excess with a paper towel if necessary, then wash thoroughly with water.

• Allow a cure period of at least 4 weeks before starting to use your soaps.

How much water should I use?

• If you're using commercial washing soda (with a concentration of between 30 and 35%), don't add any more water- the soda is already diluted in an appropriate amount of water.

• If you are using solid soda, you will need to dilute it with water. Preferably use demineralised water, especially if your water is hard. The calculator will give you a range of acceptable water quantities.

The table below shows the effects of a rather low or rather high quantity of water (within the recommended range) to guide your choice.

1. A low quantity of water

Saponification speed

Saponification is faster and the paste thickens more quickly (the "trace" appears more quickly).

Addition of additives

The paste can quickly become quite thick, so you will need to add the additives very speedily (bearing in mind that some additives can still accelerate the reaction) to ensure they are well combined before the dough hardens too much.

Additives containing water (milk, fruit or vegetable purées, etc.)

Allows a greater quantity of "wet" additives to be added at the end of the saponification process.

Creating artistic effects

To create marbling or other effects, you'll need to be quick. However, it's easy to create "whipped cream" effects on the top of the soaps with the thickened paste.

Temperature rise

Tendency to increase temperature

"Gel phase" (see insert below for explanation)

A "gel phase" is less common in formulas with little water.

Drying time

Reduced drying time (unless a large quantity of water-containing ingredients is added at the end of the saponification process)

Results

If very little water is used and no "wet" ingredients are added, the soap may be too dry and prone to cracking.

1. Large quantity of water

Saponification speed

The paste will thicken more slowly.

Addition of additives

This leaves more time to add additives and incorporate them evenly.

Avoid adding too many "wet" ingredients at the end of the saponification process, as the soap may then contain too much water (and require a very long drying time).

This gives you time to separate the paste into several differently coloured parts to create marbling effects.

Temperature rise

The temperature rise is generally lower.

"Gel phase" (see insert below for explanation)

Formulas with more water more often go through the "gel phase".

Drying time

Longer drying time

Results

The soap will retain a softer, more elastic texture for longer.

To begin with, we recommend that you choose the middle of the range, or a value in the top half of the range, so that you have time to observe the different stages (gradual thickening of the paste) and make your additions and adjustments calmly.

If your recipe is very rich in "solid" butters and oils (Coconut, Babassu), the paste will tend to thicken quickly, so choose a high amount of water (value in the top half of the range).

Oils and butters

For additional fatting with a specific oil or butter, whose properties you want to take full advantage of, add them at the end of the preparation. As the saponification reaction is well advanced at this stage, the additional oil will only be slightly attacked by the soda.

Depending on the "soda reduction" chosen when calculating the soda, you can add up to around 10% of oils as additional superfatting (avoid having more than 12 to 15% "total superfatting", otherwise your soap will be too soft and go rancid more easily).

• Nourishing: Avocado, Sweet Almond, Olive, Wheat Germ, Argan, Macadamia, Sesame oils, etc.

• Anti-ageing and revitalising: Musk Rose, Raspberry, Evening Primrose, Borage oils, etc.

• Soothing: Calendula oily macerate, Raspberry oil, Cranberry oil, etc.

• Purifying: Nigella, Neem, Calophylla inophylla oils

• For a very rich, creamy feel: Shea, Mango, Cocoa, Tucuma butters, etc.

Colours

• Mineral colourants: mineral oxides, ochres, micas, coloured clays. For more even colouring, we recommend pre-dispersing these insoluble colourants in a small quantity of water or oil (which will then add an additional fat). Test beforehand what disperses them best, depending on the colours you're using. It's also possible to add them directly to the soap mixture at the "trace" stage, blending well afterwards to disperse the colourant. For a very white base, add white pasting to the "trace" in your soaps.

• Plant dyes: madder or Manjishta powder ("old rose"), Urucum (magnificent bright orange), turmeric (reddish-brown), activated natural carbon (intense black, popular for marbling), caramel powder (caramel brown, to be pre-dissolved in the water before adding), nettle (green), Spirulina or Chlorella (dark green), cocoa powder (chocolate brown).

  Add the plant or seaweed powders just before the trace stage and blend with a blender. Test your powder in the presence of a little soda before you start, as some colours are altered by soda (in particular, the violet tones of anthocyanins such as beetroot juice or hibiscus powder turn grey and then brown). Plant powders can also be used in the form of an aqueous or oily macerate (depending on the solubility of the pigments) for a softer, grain-free result: Urucum macerated in oil gives an orange oil that will add colour to the soap (use it in your saponifying oil mixture for an intense result). Madder can be infused in soda water.

• Coloured oils: adding Buriti oil, Wheat germ oil, Carrot macerate or Calendula macerate will add extra fat while slightly colouring the soap with a yellow-orange note.

Perfume

It is very difficult to predict how odours will hold up in cold saponification.

• Essential oils: the way in which their fragrance remains in the soap and the way it is reproduced varies enormously depending on the essential oil. Generally speaking, the "base notes" will hold best, whereas volatile notes, particularly citrus, will be difficult to fix in the soap (to improve their hold, combine them with strong base notes). Add essential oils at a rate of 1 to 5% (in relation to the total weight of the oils) to your soap.

• Essential oils that last well in soap:

  • Long-lasting base notes: Patchouli, Vetiver, Cinnamon, Nutmeg, Clove, Atlas Cedar, Amyris

  • Powerful heart notes: True lavender, Rosemary cineole, Peppermint, Spearmint, Thyme linalol, Palmarosa, Scots pine, Petitgrain bigarade, Black spruce, Geranium, Ylang-Ylang, Coriander, Hô wood

  • Intense top notes: Lemon Litsée, Lemongrass, Ginger, Eucalyptus, Bitter Almond

• Natural cosmetic fragrances: here again, the scent is very unpredictable. They should generally be used in high proportions (at least 3-5%). Fragrances such as Eastern Touch, White Lilac, Body butter, Bee happy, Amber Treasure, Wild blackberry, Baby doll and Angel’s Touch generally give good results.

  Natural aromatic extracts do not hold up well in cold saponification.

The smell of saponified plant oils generally disappears completely. It is sometimes possible to retain a little scent with oils or butters added at the end of the preparation process (sesame oil or cocoa butter, for example).

Other ingredients: according to your creativity...

• Honey powder, liquid honey (moisturising, softening). Be careful, honey tends to accelerate the trace and also turns the soap brown. Honey soaps can also heat up quite strongly if you use a large mould.

• Colloidal oatmeal powder: very popular for sensitive skin, to be added at the "trace" stage.

• Milks: We recommend using powdered milks so that they can be easily incorporated into the "trace" without adding too much water to the soap:

  mare's milk or donkey's milk powder for a very soft, creamy feel and nourishing, soothing properties. Milks tend to turn soaps brown.

• Scrubs

• Fruit or vegetable purées: carrot, avocado, banana, etc.

• Dried flowers or plants, seaweed, etc.

If you add liquid ingredients or ingredients containing a lot of water (milk, purées), make sure you don't add too much or you'll end up with a soap that's too soft, takes a long time to dry or doesn't keep well. If you intend to add liquid ingredients at the end of the preparation, use a quantity of water at the lower end of the range recommended for dissolving the soda.

Antioxidants

If you are making soaps that are heavily superfatted with oils that are sensitive to oxidation, you can add Vitamin E (0.1-0.2%) or Rosemary CO2 extract (0.1-0.4%) at the "trace" stage, to prevent rancidity and extend the soap's life.

Stage 1: calculations

This is a very important step, because if the calculation is not correct, the soap may be caustic, i.e. corrosive to the skin.

Whatever the source of your recipe, we recommend that you always check the amount of soda indicated.

To make this easier, we've provided a calculator here. The results will appear in a results sheet that you can save or print out.

The soda calculator allows you to determine the amount of soda theoretically needed to saponify the oils in your blend. This quantity is then 'reduced' to ensure that there is no residual soda in the finished soap. The calculator's result sheet provides a table showing the quantities of soda calculated with different "soda reductions".

In the table on the result sheet, we advise you to choose a quantity of soda with a reduction of at least 5% to have a safety margin.

• If you choose the "pure soda (solid)" option, the calculator will also give you a range for the amount of water to use to dilute the soda.

• If you're using a commercial soda lye (a ready-made solution of soda in water) , enter the concentration (in %, it should be indicated on the bottle and be between 30% and 35%).

If you wish to add additional fat at the time of tracing, simply enter the desired percentage in the appropriate box (but do not enter this oil in the calculator table). The calculator will tell you the weight of oil to add at the end of the preparation.

If you substitute one oil for another, or change your oil quantities at the last minute, you will need to recalculate the quantity of soda to be added.

Find the Aroma-Zone saponification calculator here

Stage 4: Storage

Soaps can be stored for months or even years without any problem, in a dry, well-ventilated place away from light and heat.

There are various marbling techniques for creating pretty designs on your soaps. Here are some of the best-known, but don't hesitate to come up with your own ideas!

For marbling, you need to work fairly quickly because soap paste thickens quickly. We advise you to choose a formula with a fairly high water content (top of the range) to slow the setting a little. Start adding your colourings as soon as you see a fine trace.

Industrial hot saponification

This is the type of process used to produce soaps on an industrial scale, as it allows the soda to react quickly and completely with the fats. Saponification takes place at high temperatures and in the presence of excess soda. The soap paste is "cooked", i.e. heated until the saponification reaction is complete. The paste is then washed, usually with salt water to remove the excess lye. During this operation, the glycerine is also separated from the soap and removed. This type of saponification cannot be carried out without industrial equipment.

The traditional process used to produce Aleppo soap or Marseille soap is also based on hot saponification.

Hot saponification at home

The process is similar to cold saponification, but saponification is accelerated by heating the soap paste in a bain-marie or even an oven.

The advantage is that saponification is normally complete by the end of the process, reducing the curing time. However, this involves heating the oils, which is not always desirable. On the other hand, the ingredients added at the end of the process are better preserved (particularly the fragrances).

Hot methods are much more delicate than cold saponification and require a high level of expertise. We therefore advise you not to try hot saponification unless you have good experience of cold saponification and a good understanding of the process.

A simpler variant is to carry out cold saponification, pouring the soap paste into moulds, then "baking" the soaps in their moulds in the oven (1 to 2 hours at around 80-90°C). This has the advantage of speeding up saponification and therefore reducing the curing time. However, all your ingredients will be heated and may be damaged (especially perfumes or sensitive oils added as an extra fat at the trace stage). Also, beware of "volcano" effects, as saponification is exothermic (produces heat) in itself, so there's a risk of overheating in the oven…

"Melt and Pour" soaps

"Melt and Pour" soaps are in fact soaps that have already been saponified, to which other ingredients have been added (in particular plant-based glycerine and a sugar: sorbitol) to obtain a formula that can be easily remelted in a bain-marie.

Making soaps with a "Melt and Pour" base is therefore very simple and does not involve any handling of soda. All you have to do is melt the soap in a bain-marie, add colourings, fragrances, active ingredients and exfoliants… according to your creativity, then pour your soaps into moulds. They are ready to use as soon as they have hardened, after a few hours.

"Soap-free" or "syndet" soaps

As their name suggests, 'soap-free' soaps or dermatological bars are not real soaps, i.e. they are not produced by saponifying oils.

They are mixtures of solid surfactants (often synthetic, of petrochemical origin, but some of plant origin) which are agglomerated and moulded under pressure to form soap bars. Their advantage is that they have a pH close to that of the skin, unlike real soaps, which necessarily have a basic pH. It's a shame, however, that the vast majority of 'syndets' are made from surfactants that are not very environmentally friendly (and sometimes potentially irritating too).

Find the Aroma-Zone saponification calculator here