Unlike melt and pour soaps, traditional solid soap is made using a variety of fats (oils, butters, tallow etc) which, in a liquid state, are mixed with a sodium hydroxide (lye) solution.
This concoction of fats, lye and water undergoes a series of chemical reactions known as saponification which results in soap. Chemically, soap is the sodium salts of the fatty acids contained in the original oils / butters with glycerine as an integral part of the soap ‘left over’ from the saponification process.
Soap can be created as a solid bar with sodium hydroxide, a soft soap with a dual lye of sodium hydroxide and potassium hydroxide and a liquid version with potassium hydroxide only.
Soapmaking is believed to have been a known process for thousands of years. Records have been found from ancient Babylonian times with the original process probably using animal fats and potash – the ash left over from fire.
Looking primarily at solid soap; there are a number of commonly used methods that can be used – cold process, hot process and oven hot process.
Cold Process Soap
The oils / butters / other ingredients eg sodium lactate are mixed with the lye solution, often at a similar temperature, and then combined until the mixture reaches ‘trace’ this means the spoon or stick blender will leave a trace if lifted from the soap. At this point the mixture can be poured and should no longer separate. Depending on the soap maker, this stage can be attained using slightly different methods that manage the overall temperature of the mixture or the type of trace density that will work best with particular pouring techniques that may be needed for the final soap pattern. As examples, milks or honey soaps can get very hot and create a darker colour so freezing milk as a water substitute or using room temperature methods which use the lye solutions own heat to melt any butters in the formulation.
The soap batter is usually very liquid and suitable for a wide range of simple, decorative or highly complex decorative finishes where a gravy or thin custard consistency is necessary.
Once the soap is poured, it will need to harden up and full saponification should occur within 48hrs or so of the soap being made.
Benefits of the cold process method – undoubtedly this type of soap making lends itself to an amazing array of decorative finishes
Problems that may occur – some fragrance oils (often florals) and essential oils can cause the soap to ‘accelerate’ which means it jumps from light trace to almost solid soap exceptionally quickly. This can sometimes be rescued using the hot process method. Another aspect that can be caused by scent addition is ricing which literally looks like small pieces of rice within the soap. Aggressive stick blending may help to blend this out.
Stearic spots may be more common using the cold process method particularly where low temperatures are implemented.
Hot Process Soap
The hot process method uses equipment such as a slow cooker to melt all of the main ingredients and once these are liquid, the lye solution is added. As with the cold process method, these should be combined to trace at which point the slow cooker should be adjusted to a low heat, lid added to prevent steam escaping and the soap is effectively ‘cooked’. This process does need constant monitoring as it can expand substantially and may need to be stirred back down so it does not volcano out of the cooker. By the time it has reached the ‘soap’ stage saponification is complete. Hot process makers will usually add their superfat, scent oils and a little boiling water ‘after the cook’ which can help with fluidity and also ensures these ingredients are not exposed to the lye and saponification process.
Benefits of the hot process method – the addition of scent after the cook undoubtedly removes some potential issues such as acceleration and it may be that less is required for the same effect. Adding the SF after saponification means expensive or luxury oils will be retained in the soap as oil which can be exceptionally useful for skin conditioning purposes. The soap is safe for use immediately so clean up of the slow cooker, mixing jugs for colour etc can be a lot easier.
Problems that may occur – hot process soapmaking can result in a very ‘rustic’ soap that does not have the fluidity of cold process for design purposes. There may be more air bubbles as it is dolloped into a mould at a mashed potato type of consistency and over cooking can result in a bit of a lumpy appearance. Practice and testing with the method, temperatures, ingredients and point of addition can all help to maintain maximum fluidity and beautiful soap can definitely be created using this process while retaining the benefits of any luxury additions.
Oven Hot Process or CPOP
With this method, the soap is created and moulded using the cold process method as above. The mould(s) is put into an oven that was previously warmed up on a low setting then switched off as the soap is added and it is usually left over night. Saponification will occur as per the cold process method – in the mould.
Benefits of the OHP method – this can combine the artistry available with cold process while shortening the time before the finished soap can be removed from the mould.
Problems that may occur – there is a risk of the soap overflowing the mould if it gets too warm and it can also crack. This is method that is highly likely to make the soap gel (this can intensify colours and/or cause heat affected ingredients such as milk or honey to scorch) so should probably be avoided if low temperature cold process would be more suited to no or partial gel, steeper water discounts and easily scorched ingredients.
Ultimately, there is no ‘best way’ to make traditional soap. Each method has benefits and drawbacks and these are all affected by the type of oils and butters you include, the types of scent, your intended design and your own practice, confidence and experience so you are anticipating a few steps ahead. In amongst these three ‘standard’ terms for methodology there are also a wide variety of ‘tweaks’ that can enhance different processes.
Curing of Soap
There are some myths around that HP soap does not need curing because it is already ‘soap’ when it is removed from the mould and these are completely inaccurate. The majority of the saponification of CP soap will have been completed within the first 24 hours of pouring and full soap by 48 hours.
The curing process is a period that soap requires before it is suitable to use. During the curing process, water evaporates from the soap so it hardens into shape, any lingering saponification will be completed and the fatty acids and sodium salts mentioned above will slowly finish organising themselves into a crystalline structure also called ‘soap crystals’. Soap is a little like fine wine and will age into a product that is far more luxurious than it is during the infancy stage. Fresh soap will be softer, more easily dissolve into the water during use and may feel less conditioning or have less lathering properties. Suitable curing of at least 4 – 6 weeks will skip the immediate infancy stage and allow the soap to harden, lather to stabilise and for it to feel milder in use. Some soaps such as a castille (olive oil only with the lye solution) can take a minimum of a year to cure and produce a beautifully mild but cleansing soap.
Final Thoughts
Soapmaking should absolutely be fun. Within some unavoidable parameters such as ensuring you have used a calculator such as Soapcalc to ensure the correct amount of lye is used for safety – your limits are your own creativity. Try the different methods and see which one calls to you as being the type you are most comfortable with then you can fine tune your own personal process.
