I Thought Soap Was Just Soap

I get asked this question a lot, usually when someone finds out what I do for work and their eyebrows go up a little, like they're not sure if soap making is a real job. Though we certainly don't look the stereotypical part, my answer is always the same: yes and no. Yes, all soap cleans. But beyond that, two bars sitting side by side on a shelf can be about as different as a home-cooked meal and a fast food drive-through. The process and the oils are what separate them, and once you understand those two things, you'll never look at a bar of soap the same way.

There are really just two foundational ways handcrafted soap is made: the cold-process method and the hot-process method. We use cold process at Private Oaks, and there are good reasons for that.

Cold process soap starts by combining oils and lye water at temperatures between 100 and 125 degrees Fahrenheit. The mixture is blended until it reaches what soap makers call “trace,” think pudding-like consistency, then poured into molds and left to cure for four to six weeks. That curing period is where the magic happens. Water slowly evaporates, the bar hardens, the pH gradually drops to a milder level, and the lather quality develops. A properly cured bar actually keeps improving for months. We cure ours for a minimum of 45 days.

That usually leads to the next question I get, either out loud or written all over someone's face: Why does any of that matter? What does cold process actually do for my skin?

Because no external heat is applied during this process, the natural vitamins, antioxidants, minerals, and beneficial properties of the oils survive largely intact. But the most important thing cold process preserves is the glycerin.

Here's the chemistry behind it, simplified: when fats or oils are combined with an alkali (lye) a chemical reaction called saponification occurs. The oils break down and recombine into two things: soap molecules and glycerin. No lye survives in the finished product. What remains is pure soap and naturally occurring glycerin, and in cold process, that glycerin stays right where it formed, inside the bar.

That matters because glycerin is a humectant. It pulls moisture from the air and holds it against your skin, leaving your skin feeling hydrated rather than tight and stripped after washing.

There's one more thing we do at Private Oaks that's worth mentioning, and other quality soap makers do this too. We deliberately leave a small percentage of oils unsaponified, meaning they don't fully react with the lye. This is called superfatting. Those free oils remain in the finished bar as skin-conditioning agents, adding another layer of moisturizing benefit beyond what the glycerin already provides.

None of this happens by accident. The oil blend, the lye calculation, the temperature, the clays, and the salts all affect the final bar. Cold process requires patience and precision. That's exactly why we chose it.

The other foundational method is hot process. It uses the same base ingredients as cold process, oils and lye water, but external heat is applied during saponification, typically through a slow cooker or crock pot, at temperatures exceeding 150 degrees Fahrenheit. The heat cooks the soap through saponification in a matter of hours rather than weeks. Most tallow-based soaps are made this way as well.

Because saponification completes during the cooking phase rather than inside the mold, hot process soap is technically usable as soon as it hardens, usually within 24 to 48 hours. That's a significant difference in turnaround time compared to cold process.

Other differences? Hot process bars have a distinctive rustic, textured, and sometimes uneven appearance. When the soap batter is poured, it has a thick, applesauce-like consistency that makes intricate swirls and detailed designs very difficult to achieve. If visual craftsmanship matters to you as a maker, cold process gives you far more creative control.

At the end of the day, hot process is still a true soap. The glycerin remains. It's made from real oils, or in some cases tallow, and it cleans effectively. The higher heat can slightly degrade sensitive essential oils and botanical additives, and the lather tends to feel a little less silky than cold process, but fundamentally, both methods produce the same thing. It's soap. The difference between them comes down to time, texture, and creative range. We chose cold process because we care about all three.

I'll quickly touch on four other methods of soap production, with the last one being the most relevant to most people's daily lives.

Melt and Pour

Melt and pour starts with a pre-made soap base that has already been saponified by a manufacturer. The maker melts it down, customizes it with colors, fragrances, and additives, and pours it into molds. No lye handling is required because saponification already happened before the base arrived. The person using melt and pour is not making soap from scratch. They are crafting with someone else's formula.

Most commercial melt and pour bases contain the expected soap ingredients plus additional agents that make them re-meltable, often extra glycerin, surfactants, and sometimes synthetic additives like SLS (Sodium Lauryl Sulfate) depending on the quality of the base. Melt and pour is not inherently bad. The quality entirely depends on the base being used. But because the maker buys a pre-made formula, they have zero control over the ingredients that matter most and have to take the manufacturer's word for what's actually in it.

Rebatch

Rebatch, also called hand-milled soap, takes an existing cold or hot process soap, usually a batch that went wrong somewhere along the way, grates it down, melts it with a small amount of liquid, and re-pours it. It's a rescue method. The result is still a true soap made from real oils, though the texture tends to be rough and rustic. Our Laced bar is a creative cousin of this concept, using the remnants and offcuts from our other batches in a purposeful, intentional way rather than letting anything go to waste.

Liquid Soap

True liquid soap uses potassium hydroxide (KOH) instead of sodium hydroxide, which is the lye used in bar soap. Potassium hydroxide produces water-soluble potassium salts of fatty acids, which is what makes the result pourable rather than solid. It's made using a hot process method that requires several hours to fully saponify, producing a thick, translucent concentrate that is then diluted with water. You cannot simply dissolve a bar of soap in water to make liquid soap. The molecular structure is different and the result will separate, clump, or turn slimy over time.

One important distinction is worth making here. Most commercial liquid soaps and hand wash products are not true liquid soap at all. They are synthetic detergents, surfactant-based products that are cheaper and easier to manufacture at scale. What's in your pump bottle is almost certainly not what the chemistry above describes.

Commercial and Industrial Soap

This is what most people think of as soap and what most people are actually using every day. It is also fundamentally different from everything described above.

Large manufacturers combine tallow and/or inexpensive plant oils with lye, apply high heat, and saponify in massive quantities. Then they do something that changes everything: they remove the glycerin. Glycerin is more valuable as a standalone commercial ingredient than it is inside a bar of soap, so manufacturers extract it and sell it separately for use in lotions, cosmetics, and food products.

The follow-up question I always get at this point is: "Well, what's left?"

What's left is a dried soap base that gets mixed with synthetic fragrances, artificial colors, preservatives, foam boosters, and in many cases synthetic detergents like SLS (Sodium Lauryl Sulfate) and SLES (Sodium Laureth Sulfate). Technically speaking, the result is not soap at all by the FDA's legal definition. The FDA defines real soap as a product composed primarily of the alkali salts of fatty acids. Many commercial bars don't meet that standard, which is why they are legally classified as cosmetics or detergents and labeled as "beauty bars," "cleansing bars," or "body bars" rather than soap.

So what do SLS and SLES actually do to your skin? These industrial surfactants strip the skin's natural lipid barrier, the protective oils that guard against moisture loss, bacteria, and environmental damage. The result is dryness, irritation, and in people with sensitive skin, eczema flares and allergic reactions. These are the same compounds used in floor cleaners and industrial degreasers. A 1983 study found that SLS caused skin irritation at concentrations as low as 2 percent. Most commercial bars contain between 15 and 20 percent.

The business model behind all of this is worth understanding. Commercial companies strip the glycerin from their soap, sell it to their own lotion and moisturizer divisions at a higher margin, and leave you with a bar that dries your skin out, creating the very need for the moisturizing products they also sell you. It's a loop, not a coincidence.

So, isn't soap just soap? Not even close. We covered the process side of that answer here. The oils side is a whole conversation on its own, and it's one worth having. That's the next article.

Learn more about the ingredients we use on our Ingredients page.