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What is soap, and what makes ours so special?

July 19, 2022

A lot of times, when people think of lye soap, they think of an old cauldron and soap so strong it'll melt your skin. While that might have been how it was made a long time ago, things have come a long way since then.


What is lye, you might ask?

Lye is Sodium Hydroxide. It is a caustic base processed from sea salt.

There's a lot of creativity and artsy fun stuff in soapmaking, but there's also a ton of science!

In order to make true soap, you need a base (sodium hydroxide) and an acid (your fats and oils). When you combine the two, you get a salt - or soap!

The oils and fats you choose can vary on your recipe. There is this thing called SAP value. SAP stands for saponification. Saponification is the process of the lye reacting with the oils and fats. SAP value is how much lye it will take to convert this particular fat or oil into soap. Like making cookies, you wouldn't just decide to throw a bunch of ingredients together and hope it properly bakes, it's the same thing with a soap recipe.

Each oil and fat has its own SAP value. Luckily, there are lye calculators online to find these values. It saves me a lot of math 😂

Each oil and fat also have their own qualities that they add to a bar of soap. Some help with lather, some help with the hardness. Some make it creamy, some make it light.

How does soap clean?

A soap molecule has one end that likes water (hydrophilic) and another end that doesn't like water (hydrophobic). When you rub the bar on your skin, the hydrophobic end clings to the oil and dirt on your skin, while the hydrophilic end looks for the water. When washed off, it pulls the dirt and oil with it.

How do you make soap?

You first combine the lye with water. This creates a chemical reaction. The solution can get up to 140 degrees! You then melt your solid fats down and combine them with your oils. Both lye and oils need to cool down and reach the desired soapmaking temperature. I like to make mine below 120 degrees. Once they're ready, you combine and stir until they come to your desired trace. Trace is the consistency of the soap. I like to get mine to medium trace, similar to a melted milkshake. After this, you pour the soap into the mold and let it sit and harden for 24 hours. When you're making hot process soap, you continue to let the soap cook until it's more like mashed potatoes.

What's the difference between hot process and cold process soap?

In hot process, you use an extra source of heat such as a crock pot, oven, or stovetop. This speeds up saponification, and your bars do not need to cure. Cold process does not use an extra source of heat. The only heat in this process is from the energy of the reaction between the fats and lye. These bars will need to sit and cure for 4-6 weeks to make sure they're all finished up. I like to make both methods.

Will lye soap strip and dry my skin?

It doesn't have to! There's this handy little thing called super-fat. You can use this to ensure that your soap bar is actually moisturizing instead! When you super-fat your soap recipe, you are leaving a percentage of fats and oils un-saponified. This means they do not react with the lye and are in the soap to moisturize. I like to use a 3-5% super-fat, depending on my recipe.

Another reason lye soap can burn your skin is if the soap wasn't properly mixed.

Why should I use homemade soap?

Homemade soap has so many benefits. You can also find bars that suit your skin's needs without all the nasty chemicals. There can be a lot of unnecessary ingredients in store-bought soap. Remember, it's cheap for a reason. A lot of people think that they are buying soap from the store when they quite possibly could just be using skin detergent. 😢

Is all homemade soap natural?

Unfortunately no. A lot of people have different ideas as to what natural or healthy means. There are a lot of homemade soaps out there that are still laden with fragrance oil, synthetic dyes, glitter, and not environmentally friendly oils.

Things you might want to watch out for on homemade soap labels are:

  • Fragrance oils - a big no-no for the endocrine system.
  • Synthetic colorants. This can also include iron oxides.
  • Palm oil - a lot of palm oil is not sustainably harvested from rainforests. You can find palm oil that is sustainably harvested; just something to be aware of.
  • Canola oil - Blech. If I wouldn't eat that, why would I rub it on my skin? Same with corn or soy oil.
  • And Mica. Some people feel like this is healthier because it is a mineral. This is totally a personal preference, but I choose not to use it because I can't guarantee the quality, and I also don't know if the labor laws were fair for the people harvesting it.

There are lots of soap makers out there who pour their hearts into their products and desire to have high-quality, healthy soap! You just have to be aware as the consumer.


Over the last several years, I've been using different recipes to see what I like best.

The soap that I'm now making is with lard, tallow, castor oil, and essential oils.

I love that the lard comes from our hogs. I know exactly how they were raised and what they were fed.

I source my tallow from local grass-fed and finished operations as well.

The castor oil helps with the lather. While lard creates a very creamy and rich bar of soap, it doesn't lather very well and needs some help!

I love blending essential oils and coming up with refreshing scents. Occasionally I'll throw some herbs in there for fun colors!

I try to keep my packaging as environmentally friendly as possible.


I hope this cleared up some questions you might have had about lye soap!


Until next time,

Kait Kesten

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