The Science of Soap Making: How to Craft Custom Bars at Home

Soap has been used since the Ancient Middle East times and there have been different ways in which it’s been made over the years. It wasn’t until around the 15th century that soap became a common household item thanks to widespread manufacturing, and now it’s a massive industry that creates around $38 billion per year.

There are plenty of soaps available, too, with some being more “luxurious” and costing more than $10 per bar while others are still cheap at around $1. Then, there are people who prefer to make their own soap. It might sound a little intimidating to make your own, but it’s actually easier than you think. If you’ve been wondering how to craft your own custom bars at home, here is all you need to know about the science of soap making through the several different methods available.

For starters, you’ll need some common equipment for most methods of soap making. This includes a digital scale, spoons/spatulas, molds, containers (stainless steel is preferred), and a thermometer.

Cold Process

Cold process soap making is one of the most popular methods, and it’s one that requires lye. You should know that when handling lye, you need a lot of safety equipment so that you don’t damage your skin and eyes. With that said, make sure that you’re handling lye with gloves while wearing long sleeves and goggles. From there, you’ll want to gather your oils which include shea butter and olive oil.

Once you have the lye and water weighed out and ready to go, slowly pour the lye into the water. Try not to breathe in too deeply as there will be a lot of fumes. Stir the mixture until the lye has dissolved. Let the mixture cool, which can take around 60 minutes. During the cooling process, melt your oils until they reach 100 degrees.

The lye mixture can then be added to the oils, then stirred until your soap has a thick batter-like consistency. By this point, you should have a mold prepared to pour into. After pouring, cover the mold with both paper and a towel, allowing it to cool for 48 hours. Once your soap is cut into bars, you’ll still need to let it sit in the open air for about a month before it’s ready to use.

Hot Process

There really isn’t too much of a difference between the cold process. The main difference is that instead of melting your oils in a pan, you do so in a Crockpot or other slow cooker. This creates a better overall mixture, and the process of adding the lye and stirring the mixture can take up to two hours. The fragrances are added after the soap has gelled, and it doesn’t take several weeks for the soap to be ready to use.

Instead, you can end up using hot process soap on the same day in the right situation. Once the soap is hardened, it’s ready to use, but you might still want to wait. Giving the soap four to seven days of sitting out allows it to harden more and will create a longer-lasting bar. Hot process is actually the preferred method for those that make their own soap, especially because the scents tend to last longer, too.

Melt and Pour

If you want to switch things up a bit, the melt-and-pour method is a great way to save a lot of time and space. First, you’ll want to measure the amount of fragrance oil that you’ll be using in a small glass (and only glass) container. Then, take out your soap base (which is usually available in about two-pound blocks) and cut them into small cubes of the same size.

Add the cubes into a pitcher until you hit 16 ounces, while your fragrance should be a half-ounce. Instead of a slow cooker or pot to melt everything, you just need to put the soap base in the microwave for one minute at first. Stir the mixture and continue to heat for 20 seconds at a time until the soap base is completely melted.

Next, you’ll want to add a few drops of dye if you want to change the color of the soap, stirring it in and heating it for 10 seconds at a time if needed. Then, add your fragrance and continue to stir well. Pour your soap mixture into the molds then spray with rubbing alcohol to allow the soap to harden faster. After about 24 hours, your soap will be hardened and should be ready for use, though you may want to place the soap into the refrigerator for 20 to 30 minutes at the end for extra hardening.


The final soap making method we’ll look at is rebatching, which takes any failed previous attempts and corrects them. Cut down the soap that you previously made and place it into a slow cooker. Once melted, continue to stir and add in fragrance oil and add a small amount of dye (or even cocoa powder) for color.

Then, place the soap into a mold and allow it to cool for around 24 hours. Like melt and pour, adding it to the fridge at the end speeds up the process. It’s a simple way to fix any previous mistakes.

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