Guide To Cold Process Soap Making

Safety measures

There are some safety issues to consider. Working with corrosive substances is dangerous, and accidents can happen if some basic rules are not followed.

Always work with gloves, wear long-sleeved clothing, possibly with an apron or robe over your clothes. Protect your eyes by wearing glasses, wear gloves even when washing dishes and utensils after work, as soap batter is still reactive when fresh.

Always when preparing hydroxide solution, caustic soda should be added over water and not vice versa. Even so, the prepared solution will heat up and give off vapours that should be avoided being inhaled. Prepare the hydroxide solution in well-ventilated areas, possibly under a hood. Allow the hydroxide solution to cool to a temperature as close as possible to that of the oils used in the recipe. The containers in which the hydroxide solution is prepared must be resistant to high temperatures and must not be used for other purposes.

For your safety keep a bottle of food grade vinegar on the workbench while making soap, in case you spill from the hydroxide solution, you can neutralize using vinegar.

When blending, avoid introducing air bubbles into the mixture and avoid spilling or splashing the mixture on the work space. Protect the table you are working on with a tablecloth or other material as the hydroxide solution can sweep or stain surfaces.

When preparing soap, make sure there are no children or animals around that could come into contact with the substances, label your containers with solutions or substances and keep them out of the reach of children

Equipment

In order to make soap, you will need the following tools/equipment:

- an electronic (kitchen) scale, preferably accurate to at least one decimal place in case you need to measure quantities below 1 g
- a vertical blender for blending. You can also use a spatula if you don't have one available, but the process will take considerably longer.
- gloves, as we work with corrosive substances, we need to protect our hands
- goggles to protect the eyes from splashes
- heat-resistant pots, stainless steel or enameled pots, plastic containers that withstand higher temperatures used for mixing, melting or heating oils
- Berzelius beakers or other heat-resistant containers used to prepare the NaOH solution which can be raised to 100°C
- silicone spatulas or plastic or stainless steel spoons with which to dose and mix ingredients
- pots/bowls for weighing various ingredients
- silicone moulds or forms for pouring the soap composition

It is recommended that the pots and tools used to produce soap are used exclusively for this purpose. It is also a good idea to prepare more containers than necessary in case different ingredients need to be weighed or portioned. The volume chosen for the containers in which to mix the soap composition is recommended to be larger than the final composition because during mixing with the blender, the dough may splash out

Other equipment you may still need:

- bathroom/marine pots/pans
- stove or hob to heat ingredients
- a suitable thermometer to measure the temperature of liquids
- mini-mixer to mix dyes or other additives
- Pasteur pipettes for dosing small volumes of liquid ingredients
- sieve for powdered substances
- soap cutting tools, knives and wooden or plastic worktops
- paper towels and kitchen towels for cleaning
- a pump bottle filled with 70° sanitary alcohol or 96° pure ethyl alcohol for spraying the poured soap and cleaning the workspace

How to work

Before you start making soap have all utensils and equipment ready on the workbench, within easy reach. Place the scale in the middle of the table and around the scale the containers you will be working with

Do the weighing of substances required from the recipe: e.g. caustic soda, distilled water and oils. After weighing, the oils can be placed in a sea bath or in a microwave oven for melting or heating.
Once you have all the materials weighed, you can proceed to soda dissolution caustic in water

Then remove from the workbench the equipment that is no longer needed and prepare the vessels in which the soap composition will be prepared. Place the mixing bowl in the centre of the work area. The heated oils, sodium hydroxide solution, recipe and blender will be placed around the bowl.

In the mixing bowl, pour the heated oils over which you slowly pour the hydroxide solution, both at 35-50°C

Immerse the blender taking care not to introduce too many air bubbles into the mixture and blend. The mixture will start to become milky opaque once the oils and sodium hydroxide have started to emulsify. Continue blending with the blender and possibly alternating with a spatula until the mixture reaches the consistency of a smooth, soft pudding

The moment you can draw lines with the blender on the surface of the mixture and they paste their shape for a while you have reached the "trace". Depending on the oils but also the additives you use, this can happen after 5-15 minutes of blending. Various substances such as essential oils or fragrances, clays or waxes can speed up the production of the trace, the water discount too. Some additives are added at different stages of the trace for this very reason, they can thicken the composition a lot, making it more difficult to pour into moulds

Once you have reached the desired level of consistency of the dough, you can proceed with pouring the mixture into the moulds. For patterned shapes, it is preferable for the dough to be more fluid, and if you want to make patterns on the surface of the soap, it should have a thicker consistency.

Spray the soap surface with alcohol to limit the formation of sodium carbonate (caustic soda reacts with CO₂ from the atmosphere and a white film appears on the surface of the soap).

After pouring into moulds, place the soap in a clean, dust-free place and leave to cool and solidify. This can take between 1-3 days depending on the recipe. If the soap is still soft to the touch, it can be left in the moulds for a few more days or placed in the fridge to harden.

Once the soap has hardened, remove from the moulds and cut if necessary with a knife or special soap cutting equipment.

Removing from shape, cutting and ripening soap

After curing, the soap can be removed from the mould and cut as required. Kitchen knives or special soap cutters can be used. Cut soaps can be 'cosmetised' around the edges with a vegetable peeler to give a more finished look.

Soaps should be stored in clean, dust-free rooms, preferably on shelves or in crates with enough space between them so that air can circulate freely and facilitate drying. If you don't have a special room for soap maturing, they can be stored in boxes and covered with paper towels to prevent dust from settling on the surface.

The soaps are left to mature for a minimum of 4 weeks. Best results are obtained after 6 months. Do not use unripened soaps, as the composition of the soap is still reactive and in contact with water can cause stinging on the skin.

If you want the soap to go through the gel phase, immediately after pouring it into the moulds, while it is still warm, you can cover or wrap it with foil, kitchen towels or blankets (it insulates).

Cleaning of equipment and space

You can choose one of two options:

(a) after all operations have been completed, place the dishes and utensils in the sink and wash in the usual way with hot water and dishwashing liquid. Wear gloves for this stage as well because the soap composition is still reactive. Clean dishes with paper towels to remove as much of the oily substances as possible and make them easier to wash.

b) some soap manufacturers prefer to place all used dishes and utensils in a household bag after all operations are completed and allow the soap composition to harden on them.

The next day remove the hardened soap from the dishes and wash them as usual with water and detergent.

Terms and definitions

Soap - a product obtained by saponification of fatty acids or fats with solutions containing sodium or potassium hydroxide, and which together with water is used for cleaning

Saponification - a reaction in which a fat (vegetable or animal) in combination with a strongly alkaline substance: sodium hydroxide (NaOH) or potassium hydroxide (KOH) forms glycerin (a humectant) and a fatty acid salt called "soap". When sodium hydroxide is used, a solid soap is obtained. Using potassium hydroxide results in liquid soap. This is the only way to obtain 'real' or 'traditional' soap. During the saponification process, the soap composition will heat up, even when working cold or with substances at room temperature. The working temperature of the sodium hydroxide solution and oils used in soap making is between 35-50°C. It is preferable that the two substances to be mixed are at approximately the same temperature. It is also possible to work with solutions and oils at room temperature, except that the saponification process will take longer and more mixing will be needed

Exothermic reaction - chemical reaction whereby heat is released. When working with caustic soda, it will always be dissolved in water, not the other way around. Never put water on top of sodium hydroxide as a violent reaction will occur

Marine/water bath - "bain marie", a pot filled with water that is brought to a boil, used to melt or gently heat various products, such as oils used in soap making, without them coming into direct contact with the heat source

Syndet - The word comes from the combination of the terms "synthetic" and "detergent", and these are products containing synthetic ingredients and resulting from the mixing of surfactants or detergents derived from oils, fats or petroleum products that are processed through numerous chemical processes other than traditional saponification

Superfat - is a term used in the manufacture of cold process soaps that refers to the amount of fat remaining free after the saponification process is complete. It is specifically calculated in the formulation of a recipe and expressed as a percentage. Basically, it is a reduction in the amount of soda needed to saponify the entire amount of oil used in the recipe, usually between 1-10%. By keeping a quantity of unsaponified oils, the soap will be more moisturising, but it is also practiced if the recipe contains a high amount of vegetable butters that are solid at room temperature to prevent the soap from becoming too hard or crumbly

Water discount - reducing the amount of water used in the recipe, usually by 5-15%, to speed up trace production, harden the soap and get it out of shape faster

Trace - term used to describe when the "dough" composition begins to thicken and has the texture of a pudding. It is the result of emulsifying the fat with the sodium (or potassium) hydroxide solution and can be of 3 types depending on how thick the composition is: light, medium or thick. Depending on how much the composition is blended with the blender, different levels of trace can be reached, the more emulsification, the thicker the dough will become. Once the right level of trace has been reached, the prepared soap can be transferred into moulds. Allow to stand for 1-2 days depending on the recipe, during which time it will harden. Once the soap has hardened, it can be cut in the case of block moulds or removed from the moulds and matured

Freezing - the stage through which the final composition of the soap passes, after isolation, and has the effect of changing the appearance of the product, making it more translucent in some areas, or it may cover its entire surface. This stage may be influenced by the temperature at which the soap is stored after it is moulded or by the amount of sugars present or added to the composition, and only has an aesthetic influence on the finished product. Soaps that have not gone through the gelling phase remain more matte and their quality is not affected by this aspect

Emulsification - is defined as a process by which a liquid is dispersed in another immiscible liquid by mechanical mixing. Good examples of emulsions are mayonnaise, creams (lotions) or homogenised milk

Ripening - the process the prepared soap goes through to cure. During this time the water contained in the soap will evaporate, forming a strong, long-lasting soap that is gentler on the skin. Maturation of soaps is usually carried out in rooms or places free from dampness, on shelves or in crates that allow as much surface area as possible to come into contact with air currents. The maturing process takes a minimum of 1 month, preferably 6 months, but can be extended to 12 months in the case of some soft-oil soaps. Freshly prepared soaps should not be used until they have been left to mature for at least 4 weeks, some recipes produce soaps that are still soft even after they have been removed from the moulds.

Caustic soda - or sodium hydroxide is a white, strongly alkaline (basic), naturally occurring, white crystalline substance in the form of flakes, pearls or powder, corrosive and hygroscopic (attracts water). It is soluble in water and produces an exothermic reaction (heat release) in contact with water. During dissolution of caustic soda in water or other liquids, caustic vapours will be formed, which should not be inhaled. Therefore work in a well-ventilated room when preparing sodium hydroxide solutions. If this is not possible, work under a fume hood (exhaustion niches)

Distilled water - also called demineralised water, is water from which impurities have been removed by the distillation process, which involves boiling water (steaming) and then condensing the resulting vapour in another container. Other production processes also include deionisation and reverse osmosis. It is chemically pure water. When preparing sodium hydroxide solutions it is necessary to use distilled water because caustic soda can interact with impurities contained in ordinary tap water

Isolation - a process that prevents the soap composition from cooling and encourages it to enter the gelling phase. This involves covering the mould in which the soap is poured with various materials to maintain a high temperature for a period of time. This is not a mandatory step in soap making, some manufacturers opt to let the soap cool to room temperature. If the temperature is not uniform throughout the composition, after the soap hardens and can be removed from the mould or cut, the colour or texture may be different in the areas where gelling has occurred. The quality of the product is not affected. The curing time differs according to ambient temperature and recipe, and care must be taken that the soap does not overheat, resulting in cracking or bursting of the composition and its leakage from the mould

Soap calculator - tool used to calculate the required proportions of ingredients to be added to the recipe. There are numerous online calculators that also give indications of the properties of the oils chosen, the amount of fragrance/essential oil recommended and options for reducing the amount of water used or increasing the amount of oil left free after saponification (superfat). These calculators are based on the saponification value specific to each oil/oil and display the amount of sodium hydroxide and water needed to prepare a given amount of soap chosen by the user

Oils and greases (vegetable fats) - are a mixture of triglycerides, can be extracted from the seeds or fruits of various plants and form soap in reaction with sodium/potassium hydroxide. The best soaps result from combining different types of oil, but there is also soap made from a single oil: Castile or Marseille soap - made only from olive oil. Most oils are not recommended to be used at their maximum percentage because the soaps obtained can be too soft (in the case of fluid oils) or too hard (in the case of butters), so combinations of oils and butters are best, especially when the properties of each are taken into account

Saponification value - how many grams of sodium or potassium hydroxide are needed to completely saponify 1 gram of fat (oil or butter). Each oil or butter has its own specific saponification value, e.g. extra virgin olive oil has a saponification value of 0.185, which means that 0.185 g of NaOH is needed to saponify 1 g of oil.