The basic chemistry of soap
Soap, an alkaline salt, is the result of a neutralisation between an acid (the fatty acids in an oil or butter) and an alkali (sodium hydroxide solution = ‘lye’). A specific concentration and volume of lye will convert a specific mass of fatty acids into their corresponding sodium salts. If we do not have enough oil for all the lye to be neutralised, the resulting soap will be very harsh and ‘lye heavy’, containing unreacted lye – not good.
On the other hand, if we add extra oils /butters above the exact mass required to neutralise all the lye, we will be left with some unreacted oil in the soap; the resulting soap will be gentle and will have the conditioning properties of the oil – this is known as ‘superfatting’. It is a delicate balance, however, as too high a superfat will reduce the lather and lead to a soft soap.
We superfat all our soaps to ensure gentle, skin conditioning properties.
The oils we use
We divide the oils we use into base oils and nutrient oils:
- Base oils
– these are the ones which make up the bulk of the oils in the recipe – the lye solution is added directly to them to create the soap batter. The properties of their saponified fatty acids give rise to the overall characteristics of the finished soap. Our main base oils and butters are:
– olive oil (refined and extra virgin), coconut oil, shea butter
The base oils may also include:
– cocoa butter, sunflower oil, rice bran oil, extra virgin rapeseed oil
We sometimes superfat with one of these oils.
- Special nutrient oils
– these oils are added in small amounts for their specific nutrient qualities and usually contribute to the superfat portion of the recipe. Most are added at ‘trace’ (the point at which the soap batter begins to thicken, showing that saponification has started). Although the lye decides which oils it saponifies and when, we feel that adding at this point increases the likelihood of the oils’ survival through this harsh process. Nutrient oils that we often use include:
– rose hip oil, plum kernel oil, apricot kernel oil, borage seed oil, flax seed oil, avocado oil, Monoi de Tahiti, sweet almond oil, wheat germ oil as well as many others, including some of the base oils.
Properties of base oils
Refined and Extra Virgin Olive Oil:
Olive oil is a wonderful oil for use in soap, as its natural moisturising properties help form a “breathable” layer on the skin, preventing loss of internal moisture. It produces small, silky bubbles and contributes hardness to the bar. Olive oil was used for centuries to make traditional 100% “castile” soap. Pure olive oil soap is very mild, long-lasting and can be used full strength on any skin type, including babies’ delicate skin, to help retain moisture and elasticity. It is no surprise that olive oil soap soothes, nourishes and conditions the skin because it takes advantage of the natural moisturising properties of olive oil. In our soaps, olive oil makes up well over half the bar.
Like olive oil, coconut oil is a key oil in most soaps. Coconut oil contributes hardness to the bar and lots of big, fluffy bubbles. It is the only oil that can make a bar that lathers in salt water. The more coconut there is, the more bubbly the bar. However, there is truth in the adage, ‘one can have too much of a good thing’: too much coconut oil in a soap can make it drying on the skin, unless the soapmaker offsets this by superfatting at higher levels than normal.
Shea (karite) butter comes from the nuts of the African shea tree. It is wonderfully moisturising and conditioning, contributing a delicious creaminess to the lather. It contains a large percentage of ingredients that do not react with the lye, so its skin-conditioning properties are retained in the soap. It is wonderful for treating dry skin. We love shea in our soap!
We use cocoa butter to add hardness to the soap and to provide a lovely creamy lather. It helps to provide a protective layer that holds moisture next to the skin. Refined cocoa butter has no scent – this is the main form in which we use it; raw, unrefined cocoa butter has the delicious scent of chocolate – we use this whenever we want that lovely chocolate aroma as a feature in the soap.
Sunflower oil is a beautiful oil for soap making. It is high in linoleic fatty acids which are wonderfully conditioning for the skin and works synergistically with olive oil to help produce a lovely lather. The sunflower oil we use is organic, cold-pressed oil to retain maximum benefits.
Rice bran oil
Rice bran oil has been used by Japanese women for centuries, due to its nourishing, moisturising qualities. In soap, it adds to a smooth, conditioning and creamy lather.
Rapeseed oil contributes protein and wonderful moisturising qualities to soap and is high in natural vitamin E. We use a lovely cold-pressed, extra virgin golden rapeseed oil in our soap.