Cold Process Soap: What It Is and Why It Matters

⚗️ Hello and WELCOME! Today, let’s talk about saponification — the magical chemical reaction that transforms oils and fats into cold process soap and other types of soap!

“True soap” is created during saponification, which happens when a base—commonly lye (sodium hydroxide, or NaOH, for solid bars; potassium hydroxide, or KOH, for liquid soap)—combines with an acid (fats, oils, or butters). This reaction produces soap and glycerin, the natural humectant that moisturizes your skin. In chemical terms, the soap itself is made up of fatty acid salts, while glycerin—also known as glycerol—is the colorless, odorless, viscous byproduct that helps keep skin naturally hydrated. Fun fact: the word sapo in Latin means “soap,” so saponification literally translates to “turning into soap.”

Methods of Soap Making:

There are two primary ways of making true soap: the cold process and hot process methods. Other techniques exist too, including melt-and-pour, rebatching, and French milled soap, to name a few:

• Melt-and-Pour: Uses a pre-made soap base; no lye handling required. It’s quick and accessible, though the base has already gone through saponification elsewhere.

• Rebatching: Involves melting down existing soap to add new ingredients, colors, or scents.

• French Milled Soap (Milled): Soap is finely ground and mechanically reprocessed, resulting in a smoother, denser bar with a refined texture. This technique is distinct from rebatching or typical hot process soap and is prized for its luxurious feel.

There are also traditional and region-specific methods worth noting. African Black Soap, for example—known as ọṣẹ dúdú, sabulun salo, or ncha nkota—is a unique, ancestral form of hot process soapmaking. Rather than using refined sodium hydroxide (what I use here at Apothecary Addict), it relies on lye-rich ash made from burned plant materials such as plantain skins, cocoa pods, and palm leaves, combined with oils like palm oil, coconut oil, and raw shea butter. This method has been passed down through generations and stands apart as a soap deeply rooted in place, culture, and tradition.

Additionally, true glycerin soap made from scratch (not melt-and-pour) is typically produced using either the hot or cold process method, with alcohol and sugar added to dissolve soap crystals and create a naturally translucent bar. In these formulations, the glycerin formed during saponification remains in the soap, contributing to its humectant properties and distinctive clarity.

While each method has its own charm and benefits, this post focuses on cold process soap because it’s the method I use here at Apothecary Addict.

What Makes Cold Process Soap Special:

The cold process method of soap making involves carefully mixing a lye solution (the base) with a blend of oils, fats, and butters (the acids), typically at temperatures around 100–120°F. Once combined, the mixture is blended until it reaches trace — the moment when the soap batter thickens, leaving a visible "trace" on the surface, indicating that the oils and lye have fully emulsified.

Soap that has reached "trace" during the cold process method — the moment when oils and lye are fully emulsified

At this stage, botanicals, clays, essential oils, and natural colorants can be added. Adding these ingredients at trace ensures they are fully incorporated without interfering with saponification, preserving their color, scent, and skin benefits. The soap is then poured into molds. After hardening, the loaf is cut into bars and then left to cure for 4–6 weeks. This curing period is essential. It allows excess moisture to evaporate, the soap to fully develop its final properties, and the bar to become harder, longer-lasting, and gentler on the skin. The result is a beautifully balanced bar that cleanses effectively while remaining nourishing and kind to your skin.

Natural color added at trace: Indian rhubarb root powder (Rheum emodi) is blended into the soap batter, creating a rich, botanical red hue as saponification continues.

Apothecary Addict's Jewelweed Goat N’ Oat soap freshly poured into its mold during the cold process method, showcasing natural botanical colorants and a thoughtfully adorned top.

Apothecary Addict's hand-cut Desert Chaparral soap bars curing slowly on the rack, allowing time to refine their texture, longevity, and feel on the skin.

Cold Process vs. Hot Process (Briefly):

Hot process soap follows the same basic ingredients and chemical reaction as cold process soap, but the mixture is heated to speed up saponification. This allows the soap to be used sooner, though the texture is often more rustic, and there is less flexibility for intricate or delicate design work.

Cold process soap offers exceptional control over ingredients, design, and scent. Like hot process, it naturally retains all of the glycerin produced during saponification—a humectant that helps draw moisture to the skin. Both methods retain glycerin because it is a natural byproduct of saponification, but cold process allows more time for delicate ingredients to remain intact. I personally favor the cold process method because it relies on time rather than added heat, allowing the soap to form slowly and gently. This slower process helps preserve the integrity of delicate botanical ingredients and results in a smooth, creamy bar with a refined finish.

Both cold process and hot process methods produce excellent, skin-loving soap, and many skilled makers choose either method based on their process, aesthetic, and goals.

A Note on Syndet Bars (Synthetic Detergent Bars):

You may also come across cleansing bars labeled as “soap” that are actually syndet bars (short for synthetic detergent bars). These are made using synthetic surfactants such as Sodium Lauryl Sulfate (SLS) or Sodium Cocoyl Isethionate (SCI), rather than through the saponification of oils and lye.

Syndet bars are often marketed as being mild or pH-balanced, and while they can be useful in certain contexts, they are not true soap. Because they are not created through saponification, syndet bars do not naturally produce glycerin.

In contrast, some large-scale commercial true soaps, made via saponification, may have their naturally occurring glycerin removed during manufacturing, as glycerin can be sold separately for use in other products. This practice is not typically part of traditional or artisan soapmaking, where glycerin is intentionally left in the finished bar for its skin-loving benefits.

Syndet shampoo bars created at Apothecary Addict in 2019, paired with handcrafted conditioner bars — part of my broader exploration of cleansing formulations.

Cold process handmade soap offers the best of both worlds — effective cleansing and natural hydration — because the glycerin created during saponification remains right where it belongs: in the bar.

Cold Process Soap - Why Glycerin Is Amazing for Your Skin:

• Acts as a humectant, drawing moisture into the skin

• Helps protect against environmental irritants

• Soothes dry, stressed, or compromised skin

  
  

Cold Process Soap Benefits for Your Skin:

• Cleanses by lifting away dirt, excess oil, and debris

• Supports healthy sebum production — your skin’s natural moisturizer

Cold process soap matters because it honors time, ingredients, and craft—turning oils, botanicals, and patience into a bar that cares for skin in a truly intentional way.

At Apothecary Addict, every bar is handmade using the cold process method, preserving glycerin and honoring traditional soapmaking practices to deliver a truly luxurious, skin-loving experience. ❤️

Apothecary Addict's Frosted Peppermint Soap — fully cured, labeled, and ready to use, infused with French sea salt (Fleur de Sel), for a refreshing, skin-loving finish.

Curious to experience cold process soap for yourself? Explore The Classic Collection — a curated selection of handcrafted cold process soaps here at Apothecary Addict.

Want a peek behind the scenes? Follow @apothecary.addict on Instagram for soap-making magic, skin-loving tips, and inspiration!