The Science of Soap Making
The Basics of Soapmaking Chemistry:
At its core, soapmaking is a chemical reaction known as saponification. This process involves an interaction between fats or oils (triglycerides) and an alkali, usually sodium hydroxide (NaOH), also called lye for hard soaps and potassium hydroxide for liquid soaps.
Key Components in Soap Making:
Triglycerides (fats): These are esters formed from glycerol and three fatty acids, found in animal fats or vegetable oils (such as olive oil, coconut oil, or shea butter).
Sodium Hydroxide (Lye): A strong alkali to break the ester bonds in triglycerides.
Saponification Reaction:
When triglycerides react with sodium hydroxide, the ester bonds break through a process caled hydrolysis, resulting in glycerol (glycerine) and soap molecules (salts of fatty acids). The general equation can be simplified as:
Triglyceride + 3 NaOH → Glycerol + 3 Soap (Sodium Salt of Fatty Acid)
The Process:
Lye Preparation
Sodium hydroxide pellets are carefully dissolved in water, generating heat through an exothermic reaction. The lye solution's concentration and temperature are monitored rigorously, as it directly impacts soap quality.Oil Blending
The chosen oils and fats are measured and gently warmed if necessary. Different oils contribute distinct fatty acid profiles, which affect properties such as hardness, lather, and moisturising ability.Mixing Lye with Oils
Once both lye solution and oils reach appropriate temperatures (commonly 35-45°C, however whenI have I been in a rush I have defintely soaped at higher temps!), the lye is slowly added to the oils. The mixture is then stirred continuously to promote even saponification. Most soapers will blend with some kind of electric whisk or stick blender. Obviously, before electricity and the inventionof electric powered hand held devices, yes, the mixture woud be hand mixed, and it is NOT much fun. I had to hand mix once - it ook over an hour to get the soap batter to where it needed to be before I could pour it into the mould.Trace Formation
As the mixture thickens, it reaches a stage called “trace.” At trace, the soap batter will leave an faint outline when you drip a bit of the batter along the top of the mixture. This indicates the saponification reaction is progressing well.Pouring and Curing
Uusally at the point of a light to medium trace level, the batter is poured into moulds and left to continue saponifying and hardening. After approx 12-24 hours, the soap can be removed from the mould. During the following 4 to 6 weeks, the soap cures. This curing phase allows excess water evaporate and the saponification process to complete, ensuring a less harsh, hard bar.
The Effects of Fatty Acids:
Different fatty acids from the oils/butters used in making soap, affect the soap's physical and performance qualities:
Lauric and Myristic Acids (found in coconut oil plus others) produce a fluffy, cleansing lather but can be drying in high amounts.
Palmitic and Stearic Acids (in mango butter and coconut plus others) create a firm, long-lasting bar.
Oleic Acid (dominant in olive oil) results in a conditioning, gentle soap with a rich but less bubbly lather.
Linoleic and Linolenic Acids (many fats and oils) improve moisturisation but decrease shelf life in high amounts.
Soapmakers often blend oils to balance cleansing, conditioning, hardness, and lather. All soapmakers will have a blend that works for them, I have tweaked my blends over the years, sometimes based on the availability of oils/butter as well how economical they are to use.
Preservation and pH:
Soap naturally has a high pH, typically between 8 and 10 on the pH scale. This elevated pH makes it inhospitable for microbial growth, giving natural preservation. Unlike detergents or syndets bars, cold processed soap’s mild pH and natural glycerine content make it compatible and gentle on skin. Having said that, I personally wouldn’t recommend using a cold process soap on the face, as the delicate skin on the face tends to become dry for most people. There are perhaps some lovely faces that coud tolerate the high alkalinity, but from experience most won’t after prolomged use. The high pH is also what causes soap to sting the eyes. There are also some soapers who make cold processed shampoo bars, I have tried it,making really gentle shampoo bars in terms of formula, reduced lye to increase fat content as well as additonal conditioning ingredients, and for every experiemnt, it was just too drying. Al th feedback I had was also that eventually it dried the hair out. High alkalinity will do that to the delicate skin on the face and on head hair from prolonged exposure.
Some users and soapers will clai this is not true, and that their shampoo soap doesn’t do this - power to them I say and well done for finding something that works! Other soap shampoo users will follow a hair wash with an apple cider vingear rinse of some type to neuatralise the base (high alkaline soap residues), and they swear by this method to avoid excessive drying of hair.
Final Considerations: Additives and Natural Variations
Many traditional soapmakers incorporate:
Essential Oils: For subtle fragrance and therapeutic properties.
Botanical Additives: Herbs, clays, and exfoliants to customise texture and benefits.
Colourants: Natural pigments derived from plants or minerals.
Other: Salt, sugar, honey, milk, cream, vegetable purees, vegetable powders, fruit powders
While additives do not affect the core saponification chemistry, they can influence texture, colour stability, and skin feel and aesthetic.
In summary, traditional cold processed soap making is a fusion of precise chemical reactions and artisanal craft. Understanding the saponification process, fatty acid profiles, and curing dynamics enables soapmakers to create gentle, effective, and natural cleansing products aligned with centuries of hygiene science. Soap also gets better with age, it lasts longer and it just becomes an even more beautiful thing to use. I have some soaps that are almost 5 years old and they are a beauty to use & feel glide along the skin. As long as the formula being used is a stable one, meaning the fats and butters chosen are not prone to rancidity then traditional cold process soaps can be stored for many many years.
