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The basics of soap making

Ingredients:  Oils, fats & Sodium hydroxide. A lot of people are horrified to see “Sodium Hydroxide” as an ingredient but soap can not be made without it. This is what happens in the reaction when you mix fatty acids (Oils & fats) & sodium hydroxide (Lye) - it’s called saponification




Once saponification is complete you have glycerol (also called glycerin or glycerine), which is great for your skin, and the rest is the alkali salt of the fatty acid (soap) - hence why coconut oil, for example, becomes sodium cocoate after the reaction is complete. Sodium cocoate simply means fatty acid salts of coconut oil. A totally natural reaction.

The lye is no longer present after the reaction has taken place, the lye and most of the fatty acids have neutralised each other, which is why is doesn’t appear on the ingredient label.

Each oil or fat needs a specific amount of  lye for this reaction to take place effectively. 100g of coconut oil will need 18.32g of  lye to fully saponify the fatty acids in coconut oil.  Whereas 100g of olive oil will require 13.55g of lye for the same reaction. Measuring accurately is important for obvious reasons. Too much lye will leave the soap “lye heavy” and it would be rough on your skin. What soap makers do is reduce the lye by a specific amount to leave the soap with unsaponified oils or fats - this is the moisturising factor known as “Superfat”. Superfatting not only ensures that all the lye is neutralised but leaves unreacted beneficial oils in the soap which stays on the skin when you wash. Too much superfat gives a soggy bar of soap so you have to know what you’re doing.

In “Cold process” soap making the ingredients are initially kept as cool as possible (although some don’t worry about the starting temperatures). Once the lye and oils are combined there is an exothermic reaction that’s going to take place regardless. Left to it’s own devices, and depending on the additives used, this reaction can get to temperatures of over 100oC.  The increasing heat also burns off a lot of essential oils that might be used, which is annoying. The reacting mixture can be refrigerated to help keep the heat down but it takes 24 hours for the reaction to complete.

This doesn’t affect the quality of the soap but the cure time is longer, between 4 to 6 weeks. The cure time is merely the time needed for water to evaporate giving a harder bar that lasts longer.

Also, in cold process, the superfat can be any combination of the oils used - some have more unsaponifiable elements than others and the excess oils that aren’t caught by the lye is pretty random, so you can’t superfat with a specific oil and say that it’s “Enriched with” any specific oil, be wary if you see that claimed with a cold processed soap, it can’t be done.

The age old Hot process soap method goes a step further when combining lye and oils - you cook it, I use a slow cooker on low setting. The reaction is accelerated and all the lye is neutralised within a couple of hours. Once the glycerin is sparkling throughout the mix and the pH checks out okay, and the temperature is as low as you can get it while still being able to work with the batter, you can add a superfat. Then you can say that this soap is enriched with Shea butter or whatever the chosen oil is. The shea butter in the finished bar is Shea butter and not sodium sheabutterate. All additional additives, clays, antioxidants (usually vitamin E) are added just before the mixture is quickly spooned into the mould because now it’s cooling and wants to be a solid. Four of the soaps on this site are made this way; Cocoa & Honey, Manuka & Oatmilk, Bentonite Clay & Aloe Vera & the Dog soap.

With either method you have beneficial free oils for moisturising but hot process means I can choose which it should be. Hot process takes a lot longer to make but the cure time is shorter as a lot of the water is cooked off.

I like both methods for different reasons; cold process soap batter stays a smooth liquid for longer, (though you still have to move pretty fast because it’s thickening all the time), and I can mess about with patterns and natural colours a lot more. I like hot process because of the ability to add specific ingredients that aren’t altered by the reactive lye and the cure time is shorter.

Cold process soap tends to have a smoother appearance than hot process soaps but I like the rustic handmade look as much as I like the design possibilities of cold processed soap. Either method gives a soap that’s really nice to use, full of natural glycerin and cleansing and moisturising.

In commercial soaps the glycerin content is often removed as it’s a profitable commodity - this basically means that the soap then becomes a detergent, not a soap. That’s why you see “Cleansing bar” written on the packaging, not “soap” - although sometimes they add a little glycerin back so that they can use “Soap” on the label.  Natural soap feeds your skin with nourishing oils and natural glycerin which attracts moisture; commercial soap, whether bar or liquid, strips your skin and possibly feeds it with undesirable toxins.  I know which I prefer.


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