If you forgot from your sixth grade soap making science fair project, and if we are being honest, the one that your parents did for you, saponification is the necessary chemical reaction to create soap. The saponification reaction requires triglycerides (oils/fatty acids) to mix with a strong base (lye/sodium hydroxide) to form free fatty acid salts, or what you know as soap. The distribution of unsaturated and saturated fatty acid determines the hardness, aroma, cleansing, lather, and moisturizing abilities of soaps.1
If done properly, the reaction allows the acids in the oil to balance out lye's alkalinity (base), creating a somewhat neutral ph bar. Think back to any 90s deoderant commercial and you will remember, "strong enough for a man, ph balanced for a woman". There you go, that's ph. If you were lucky enough to have a pool, then you know ph from there as well.
Breaking the ester bonds is key. When the hydrolysis of the fat and oil occurs, glycerol is formed, becoming another product of the saponification process. Industrial soap manufacturers sell off the leftover glycerin to pharmaceutical companies, as the glycerin is valuable for its moisturizing properties.
In the times of ancient people [insert great aunt joke], stainless steel pots, hand mixers, and Amazon didn't exist. If you wanted a nice bar of hard soap, you couldn't grab a case of Dove from your local bulk wholesaler. Instead, you had to pray for rain during the night in hopes that your evening cook fire combined the acids and bases from dinner. This would come in the form of ash from the wood and grease from the animal fats of the prior day's catch. This meant that nature's own version of saponification would have been slightly different than today's method, as the wood ash would be potassium hydroxide based, not sodium. In essence, KOH vs NaOH.
In the days of yore, salt was added to the KOH based soap to beef it up. The difference between potassium-based soap and sodium-based soap is that potassium creates a much softer soap. Who knew that ancient Babylonians and Macedonians could have cornered the market on the hand-pump liquid soaps found in the modern day Pottery Barn style bathrooms that are common across America. This should serve as proof that you can't time the market.
As for the oils and butters used in the saponification process, the opportunities are unlimited based on your appetite for creativity and nuance. Soap making recipes feature all types of ingredients, from common and organic kitchen staples like olive oil, coconut oil, and beef tallow, to less common items like mink oil, whale blubber oil, African karite butter. The type of oil or butter used will affect a bar soap's ability to create lather, so adjust and experiment accordingly.
Craft beer enthusiast? Make beer soap. Pick your favorite hefeweizen or IPA and get started today.
No. It does, however, act as a solvent. Water aids in the diffusion of the NaOH in the mixture. Water also has an effect on the consistency of the bar soap created. If you are unsure, err on the side of too much water, as too much will give you a soft soap. Too little and there is concern for skin irritation (sodium hydroxide is also referred to as caustic soda, caustic is another word for corrosive, you see where this is going).
You know the saying, "It is like watching paint dry" ... it should really be, "It is like watching soap saponify."
The time it takes soap to saponify differs based on the soap making method used. There are two main processes, the cold process, and the hot process. Re-milling soap and the melt and pour process are two other ways to "make" soap, but they aren't legit, they are like buying a cheap guitar and swapping out the pickups for a better sound, it doesn't make you a luthier. Nor will it make you sound like Eric Clapton.
Hot process soaps will saponify a lot faster than cold process. Think in terms of hours. Watch the video below to get some reference. Cold process soaps saponify over weeks instead of hours.
The video starts 3:39 into the process. All of the compounds have been mixed. It is now at the stage where it is time to pour the mix into the molds so that it can saponify. Because he is allowing for 18-24 hours, he must be using the hot process soap making technique. After the time elapses, he pops the salt bricks out of the molds before cutting them into bars of soap. Feel free to watch the whole video to learn more.
You might be asking yourself, "How do I calculate saponification values?"
The short answer is that you don't. Use a table or calculator. Saponification tables are your friend as far as making soap is concerned. No one has time to run average molecular weight calculations or worry about long chain fatty acids and their lower carboxylic acid counts compared to their short chain counterpart.
I mean, chemists do, and if you are a chemist, then you understand fancy terms like carboxylate, deprotonation, and hydroxide ion double bonds, and what not. If that is the case, then by all means unleash your inner Koettstorfer (the MacGuyver of "Sap") and fill your garage or shed with bricks upon bricks of saponified vegetable oils. Otherwise, just stick to the charts.
When using the chart, make sure that you multiply the value by the grams. For instance, the saponification value of coconut oil is 0.19. For every 100 grams of coconut oil, you are going to want to use 19 grams of sodium hydroxide. In ounces, it would be just about 3.5.
|Apricot Kernel Oil||0.134|
|Cod Liver Oil||0.133|
|Flax Seed Oil||0.135|
|Hemp Seed Oil||0.137|
|Macadamia Nut Oil||0.138|
|Sesame Seed Oil||0.134|
|Sunflower Seed Oil||0.133|
Certain oils and waxes are considered to be somewhat unsaponifiable, while others are completely so, such as paraffin wax. Certain unsaponifiables will convey certain moisturizing and conditioning benefits to your skin. If you plan on using one such substance, like beeswax, be sure to do so sparingly.
The saponification process, while rich in molecular excitement, is extremely boring. If you are into other arts and crafts, the delay will give you time to see to those pursuits. For those of you whole are in the soap selling biz, saponification provides the time you need to research, prep, market, and sell your product.
*Caution: As always, chemical reactions can be harmful. Please be careful in all of your soap making endeavors.