Cold saponification of natural soap, why? How?
Long before shower gels and bottled cleansers, humans were already using mixtures of fats and alkaline substances to wash textiles, objects, and the body. These ancient preparations weren't always identical to the soap we know today, but they paved the way for a craft that has endured for centuries.
Cold process soapmaking employs the fundamental chemical principle of soap, adapting it for precise artisanal production: oils and butters are transformed by an alkaline solution, then the bars are molded, cut, and left to cure.
In this article, we trace the history of this process and explain what actually happens during saponification, why lye is essential, what curing is for, and what distinguishes a well-formulated artisanal soap.
From ancient soap to modern artisanal soap
The history of soap does not follow a perfectly straight line. Recipes, uses, and raw materials have evolved according to regions and eras. It is therefore more accurate to speak of major milestones than to attribute the invention of soap to a single person or legend.
The first alkaline mixtures
In Mesopotamia and Egypt, preparations based on fats, oils, ashes, or alkaline salts were used, notably for cleaning and certain bodily uses.
Organized craftsmanship
Manufacturing developed around locally available materials. In Mediterranean regions, vegetable oils already played an important role in several soap-making traditions.
Production standardizes
Advances in alkali manufacturing made production more regular and fostered industrialization. Soap gradually became a common consumer product.
The return to small batches
Artisanal soapmaking highlights formulation, curing time, ingredient traceability, and the unique character of each handmade batch.
To remember: ancient mixtures are ancestors of soap, but their composition and use could be very different from those of a modern cosmetic bar.
What is cold process soapmaking?
Saponification is the chemical reaction between fats—oils or butters—and an alkaline agent. To make a solid soap, this agent is usually sodium hydroxide, also known as caustic soda or NaOH.
During the reaction, the triglycerides present in the fats are transformed into fatty acid salts, which constitute the soap, as well as glycerin. The finished product is therefore chemically different from the oils and lye used initially.
It is called the "cold" method because the paste is not cooked for a long time. Moderate heat may be necessary to melt certain solid butters, but the reaction and hardening then continue in the mold.
A transformation, not a simple mixture: a large part of the oils does not remain intact in the bar. Their fatty acids are transformed into soap. It is the balance of the entire formula that determines the hardness, lather, cleansing power, and feel during washing.
The four main manufacturing steps
The ingredient list may seem short, but making a safe and pleasant soap requires precise calculations, controlled temperatures, and good knowledge of raw materials.
Formulate
Each oil has a different fatty acid profile. Proportions are calculated precisely to achieve the desired balance between hardness, lather, and cleansing power.
Emulsify
The lye solution is incorporated into the fats. The mixture thickens to "trace," a sign that the emulsion is stable enough to be molded.
Mold and cut
Clays, milks, plants, or other planned additions are incorporated, then the paste is poured into a mold. After hardening, the soap loaf is cut by hand.
Cure
The bars generally rest for four to six weeks in a dry, ventilated area. This period allows part of the water to evaporate.
To see the manufacturing process in more detail, consult our complete guide on the steps of cold process natural soapmaking.
The role of oils, lye, and glycerin
Oils and butters
Olive oil, coconut oil, shea butter, castor oil, or avocado oil do not all contribute the same characteristics. Some promote bar hardness, others the quantity or stability of lather, and still others modify the feel during washing.
The choice of a single star ingredient is therefore not enough to predict the quality of a soap. A successful bar primarily depends on the combination of fats, their proportions, and the superfatting provided in the formula.
Caustic soda (Lye)
It is impossible to make real solid soap without an alkaline agent. Pure caustic soda is corrosive and must be handled with protective equipment, rigorous methods, and a suitable space.
In a properly calculated and manufactured formula, the lye is consumed by the saponification reaction. It does not "disappear" magically: its elements participate in the formation of soap molecules. The goal is for no free caustic soda to remain in the finished bar.
Glycerin
Glycerin forms naturally during the reaction. In an artisanal cold process soap, it usually remains in the bar rather than being separated from the product. It contributes to the characteristic texture and feel of this type of soap.
Caution: this article explains the process but does not constitute a recipe. Handling caustic soda requires adequate training, reliable calculations, and strict safety measures.
Why wait four to six weeks?
Most of the saponification reaction occurs early in the process. Curing therefore doesn't just involve waiting six weeks for the lye to "disappear." Its primary role is to allow the bar to evolve under controlled conditions.
- Water evaporation: part of the water contained in the bar gradually evaporates.
- Hardening: the soap becomes firmer and more resistant to normal use.
- Durability: a sufficiently dry bar generally dissolves less quickly than a young, water-rich soap.
- Structure evolution: texture and lather continue to stabilize during curing.
Four to six weeks is a common duration, but some formulas require more time. The recipe, water quantity, bar size, and drying conditions all influence the result.
Once the soap arrives in your bathroom, its drying remains important. A well-draining soap dish and a location away from the spray will help it stay firm longer.
Three common misconceptions about natural soap
"Oils remain intact"
Not exactly. A large part of their fatty acids is transformed into soap. Superfatting corresponds to a proportion of fats intentionally greater than what is necessary for the complete reaction.
"Natural means hypoallergenic"
No. Essential oils, fragrances, and certain natural ingredients may not be suitable for all skin types. A simple, fragrance-free formula is often easier to choose for reactive skin.
"Soap moisturizes like a cream"
Soap is a rinse-off product whose primary function is to cleanse. A balanced formula can be pleasant and less stripping, but it does not replace a leave-on moisturizing treatment.
What distinguishes artisanal cold process soap
Choosing an artisanal soap doesn't mean seeking "100% natural" perfection. Instead, it's about prioritizing a product whose formula, manufacturing, and presentation align with your values and your skin's needs.
- Controlled formulation: the artisan chooses the balance of oils, butters, and superfatting based on the desired result.
- Glycerin remains in the bar: it is naturally produced during saponification and is usually not removed.
- Small-batch manufacturing: mixing, molding, cutting, and batch control are performed with care.
- Clearly presented ingredients: the INCI list allows you to compare formulas and identify fragrances or ingredients you wish to avoid.
- Solid format: it's easy to transport and can be presented in simple, minimalist packaging.
- Local purchase: choosing a Quebec soap maker directly supports local craftsmanship and a small team.
The color, pattern, and shape may vary slightly from batch to batch. These differences do not indicate a defect: they are part of the character of a hand-poured and hand-cut product.
Three Oréra soaps inspired by remarkable figures
History finds its way into the names of several Oréra creations. Here are three soaps currently available in the shop. Their images, names, and prices automatically update from their product sheets.
Find the bar that suits you
Compare the scents, textures, botanical additives, and fragrance-free formulas in our collection of handmade soaps.
Discover all soapsFrequently asked questions about cold process soapmaking
Is there still caustic soda in the finished soap?
In a correctly calculated, manufactured, and controlled formula, there should be no free caustic soda remaining in the finished bar. Sodium hydroxide is used by the reaction that transforms fats into soap.
What is the difference between cold and hot process saponification?
In the hot process method, sustained heat accelerates the reaction before molding. In the cold process method, the paste is not cooked for a long time: it is molded after emulsification, then the reaction and hardening continue in the mold and during curing.
Why does soap need to cure for several weeks?
Curing primarily allows some of the water to evaporate. The bar becomes firmer, more durable, and its texture continues to evolve. The exact duration depends on the formula and drying conditions.
Is glycerin added to soap?
It forms naturally during saponification. In an artisanal cold process soap, it usually remains in the bar rather than being separated from the product.
Is natural soap automatically suitable for sensitive skin?
No. "Natural" does not mean hypoallergenic. Sensitive individuals should check the ingredient list and prioritize a simple formula, without fragrance or essential oils, if these substances usually cause them discomfort.
Kristel Audet
Founder and creator of natural skincare products
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