How is soap made, anyway?

Melissa Robinson

It's kind of funny, soap.  All it is, is the combination of Sodium Hydroxide (Lye) and Fat.  Very simply put, when Lye comes in contact with fats, it instantly starts a chemical reaction known as saponification.  After a few hours, the process is complete and what you're left with is soap! 

Isn't lye highly dangerous?  YES!  In it's initial state, Sodium Hydroxide is a highly caustic metallic base and alkali of sodium.  It's used as a drain cleaner and in the manufacturing of several chemicals.  In fact, I think I read somewhere it's a by-product of producing chlorine?  (Don't quote me on that).  Safety glasses, gloves and long sleeves are necessities while soaping.  It can literally melt your skin off, so a healthy dose of respect is necessary while dealing with sodium hydroxide. 

But why would you use something so harsh in soap - especially if you're actively trying to avoid chemicals?  You cannot make soap without lye.   It's just the way it works.  Any cleansing product made without lye is not soap, it's detergent.  No lye?  No soap. 

The super cool thing about it though is that it's used only as an agent to convert the fat to soap, so while you start with this highly dangerous and caustic material, by the time it turns into soap, the lye has been used up - there is no lye present in the end product after saponification.  Think of it like a diamond made from coal - you need coal and pressure to produce a diamond, and the end result is absolutely nothing like coal!  Same principle here - you start with something extremely harsh and caustic that will melt your skin off and end up with something you can rub on your skin to clean yourself with.  Science Sorcery! 

The combination of creativity that goes along with the chemistry is simply magical to me!  More on that below.  Almost every fat and oil available can be turned into soap and every single one results in a different quality in soap.  There's hardness, cleansing, lathering, conditioning values for tons of oils and fats out there.  The chemistry part of it is figuring out what you want in a bar of soap and then formulating the right ratio of each oil to create a mixture that produces the soap properties that you're looking for.   It's not all that easy....  For example, coconut oil is amazingly cleansing and produces big beautiful bubbles in the lather - all things you want in soap, right?  Well, it's also incredibly drying on the skin.  Olive oil is super moisturizing and conditioning but produces next to zero lather and isn't all that effective as a cleanser - though all soap will technically clean.  So you can start to see how you may need to combine the two to get a bubbly soap that will clean you and not strip your skin of moisture - and then you get to figure out the ratio of each!  Some are soft, some are hard, you want a nice balance there.  There are a ton of factors to consider when formulating soap, there's no wrong or right answer and everyone has a different of idea of "good soap".   For me, my conditioning line of soaps has a combination of 6 different oils, fats and butter that I feel produces a nice moisturizing soap that leaves the skin feeling clean and hydrated.  Yay science!

Not only do you get to choose what mixture of fats to use in the soap, you can determine what scent, what color, what shape, what size, what texture, what additive, what properties do you want out of the final bar? Do you want a hard bar? Soft bar? Pretty bar? Is it for hair? Is it for face? Is it for body?  Do you want drying soap or moisturizing soap?  I mean, the possibilities are endless in what you can both create from a utilitarian standpoint and from a visually pleasing standpoint - and it drives me crazy.... in a good way!  I daydream about what to do next and color schemes and scent combinations.  It is like this untapped passion that I never knew existed, I love it! 

So how do you actually make it?  First, lye gets dissolved in some water, which then causes and exothermic reaction causing the water to become super heated upwards to 200 degrees.  Then you gotta let it cool.  In the meantime, all of the hard oils and butters in the recipe get melted down and then the liquid oils get added for a golden pool of oil ready to become soap.  Once both the oils and the lye water cools down to an acceptable level (between 80 - 110 degrees for me), the lye gets added to the oils and then stick blended. 

This will go on in short bursts for a few minutes until the soap batter starts to thicken - this is called "trace".   It can be a super light trace  or a super pudding thick trace, there's no right or wrong here, the state that it gets blended to is largely dependent on what design you have in mind for colors and/or swirls.  Part of the creativity!  At this point, colors and scents and any additives are added and then poured into a mold. 


Then it sits overnight for the saponification to complete - the next day, you have soap!!  It's at this point that it's perfectly safe to use, the lye has been safely converted, but it's still kind of harsh and the water used to dissolve the lye is still in the soap.  Next up - it sits.  The curing period will mellow out the soap and evaporate the leftover water which then results in a harder bar of soap that lasts longer in the shower.  You can technically use the soap the day after you make it, but it will last approximately 30 seconds in the shower before it disintegrates!!  You want that cure time - there is no substitute for it.  4 - 8 weeks, depending on the recipe will get ya there. 


I hope you've enjoyed this little lesson in soap!  It is super satisfying to learn the chemistry, formulate something up based on that information and then actually create it!  And on top if it, I get to share it with you all!! 


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1 comment

  • Loved the lesson. I’ve always wondered how lye works. Aren’t you something Mrs. Robinson.

    Penny Nielsen

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