Soap making terms

Definitions of some of the most frequently used terms in soap making.

A-Z

Accelerate trace/saponification
Refers to the situation where, either planned or unplanned, the saponification rate of a soap batter mixture is faster than usual, or faster than expected, which causes the soap batter to thicken quickly. There are three main things that can cause the acceleration of trace/saponification in a soap batter:

High temperatures of the oils or lye solution (or both)
Fast agitation/aggressive blending of the soap batter
Chemically induced acceleration due to the choice of base oils used for the recipe (some are known to saponify faster than others) or the addition of some fragrance oils or essential oils.

See also: soap on a stick, trace, saponification

Acid
The chemical term for any substance that measures below 7 on the pH (acid-alkaline) scale. Vegetable oils, animal fats, butters and waxes used for soap making are all comprised of various combinations of fatty acids. It is the chemical reaction between these fatty acids and the strong alkaline lye solutions used in soap making, that transforms the oils into soap. This reaction is referred to as saponification.
See also: fatty acid

Alien brains
The appearance of a wrinkled ‘brain-like’ looking surface on soap that has been warmed/processed in the oven after pouring (see ‘CPOP’) to force gel phase. This is a great article detailing some interesting experiments with CPOP and avoiding alien brains and silicone rash.
See also: Silicone rash, CPOP, gel phase

Alkali
The chemical term for any substance that measures above 7 on the pH (acid-alkali) scale. Alkaline substances are also sometimes referred to as ‘base’ (not to be confused with my use of the term ‘base oils’ for a soap recipe - which just means the main soaping oils used).

Sodium hydroxide (NaOH) and potassium hydroxide (KOH), the two alkaline substances used to make lye solutions for soap making, are highly alkaline, extremely corrosive and require careful handling and the use of personal protective equipment. Please refer to my soap making safety essentials video for information on this topic.

Sometimes people ask me if other common alkaline substances such as sodium carbonate (washing soda - Na2CO3) or sodium bicarbonate (baking soda - NaHCO3) can be used for soap making, and the answer, unfortunately, is no - they cannot. Washing soda and baking soda are also alkaline, but they do not have the strength or the correct chemical composition to saponify with fatty acids to make soap.
See also: sodium hydroxide, potassium hydroxide.

Caustic potash
Another term for potassium hydroxide (KOH), the strong alkaline substance most commonly used to make handcrafted liquid soaps.
See also: potassium hydroxide

Caustic soda
Another term for sodium hydroxide (NaOH), the alkaline substance most commonly used to make handcrafted bar soaps.
See also: sodium hydroxide

Cold process (CP) soap
Refers to a popular method of making handcrafted bar soap whereby the soap ingredients (oils and lye solution) are mixed at room temperature or slightly warmer, around body temperature, with no additional heat added to accelerate the saponification reaction. Cold process soap batters are usually poured at the point of emulsification or ‘tracing’ of the batter, after which the soap completely saponifies over the course of a few hours up to a few days, depending on the recipe. Cold process soap makers often insulate their soap moulds, once poured, to help the soap stay warm throughout the saponification reaction encouraging the soap to go through a complete ‘gel phase.’
See also: gel phase, CPOP, hot process, heat transfer method.

CPOP
An acronym for ‘cold process oven process’ whereby cold process soap is placed in a warm oven after moulding to force the soap through a full gel phase.
See also: gel phase, soap volcano, silicone rash

Cure time/curing soap
Refers to the time required for handmade soap to be stored in a dry, airy place after cutting and before use. Curing soap for at least 4-6 weeks is important for two reasons. The first reason is to ensure that the soap is as mild as possible. Most handmade soaps are fully saponified within a day or two of making, however an additional resting period improves the lather, mildness and overall quality of the soap.

The second reason for curing soap is to allow it to dry and harden as much as possible before use. Making soap with low water/liquid amounts can reduce the cure time required, however I still advocate for 4-6 weeks cure of any handmade soap, including hot process!

DOS - Dreaded Orange Spots
Pale orange, yellow or brown spots on cured soap resulting from oxidised unsaturated oils in the soap and/or the presence of dissolved minerals in the soap as a result of using hard water in the lye solution (Kevin Dunn, 2010). This is a good article about how to deal with DOS (with some great photo examples) by the Soap Queen. There is also some good, in-depth information about DOS and how to prevent it in Kevin Dunn’s book Scientific Soapmaking on my favourite books page. Handmade soap with DOS can be unsightly, but depending on the severity the soap can still be used for home/cleaning use.

Emulsion/emulsify
In the context of soap making, reaching ‘emulsion’ refers to when the soap mixture (oils and lye solution) are combined to the point where they will no longer separate. Oils and lye do not naturally mix with each other (if poured into a container without mixing they will separate into two layers with the oil floating on top), however when mixed together vigorously, the particle sizes of the oil and lye solution become smaller and smaller, and they begin to bond chemically and commence the saponification reaction and the batter will start to thicken.

EO
Short for ‘essential oil’

EVOO
Short for ‘extra virgin olive oil’

FO
Short for 'fragrance oil’

Gel phase and ‘forcing gel’
Gelling of the soap refers to a stage of the saponification process whereby a soap batter changes colour and appears to melt and become translucent (it looks like gel), after which the batter eventually cools down and the soap returns to a lighter, opaque state. Some soap makers prefer to avoid gelling of their soap in favour of the pastel, creamy colours common to ungelled soap. On the other hand, many soap makers prefer to gel their soap in order to improve the quality of the soap (gelled soaps do not absorb water in use as much as ungelled soaps do. Dunn, 2010) and to enhance the vibrancy of colour in their finished soap bar, particularly those made with natural soap colourants which can be pale and insipid in ungelled soap but very vibrant when the soap is gelled.

Soaps made in log moulds often retain enough heat with light insulation (wrapping in a blanket or towel) to completely gel without extra heat being applied. Smaller or individual moulds lose heat faster and can be more challenging to gel. The cold process oven process (CPOP) method is useful in ‘forcing’ the gel where smaller moulds are used.

The saponification reaction is an exothermic process, which means it generates heat. Some of this self-generated heat is useful in helping a soap to gel thoroughly, however some recipes and soap making methods can lend themselves to overheating, in which case the use of insulation or extra heat processes like CPOP should be used with caution. If the saponifcation reaction is too hot or too rapid, cold process soaps can ‘volcano’ out of the mould, causing a mess and ruining the look of your soap bars.

Hot process soap making is a good example where gelling of the soap is forced through the cooking process and soap often fluffs up and ‘volacnoes’ in the cooker as the saponification reaction progresses. See my hot process soap recipe videos for some good examples of this.
See also: saponification, CPOP, silicone rash, soap volcano

Heat transfer method
A method in soap making where, instead of warming/melting the soap oils before mixing with a lye solution cooled to a similar temperature, the oils are left in their room temperature (often semi-solid) state (eg. coconut oil and butters) and the lye solution is mixed just before the soap is made and is added to the oils while still very hot. The heat of the lye solution melts the cool, semi-solid oils and the soap batter is ready to mix without heating the oils or waiting for the lye solution to cool.

Hot process (HP) soap
Refers to the method of soap making whereby the soap batter is mixed in a cooking pot (usually a slow cooker/crockpot or double boiler - gentle heat is required) then after the soap has reached a stable emulsion or trace, ongoing heat is applied, which cooks the soap and completes the saponification process. As a result of this cooking process, HP soap has a different, often more chunky and rustic appearance to the smooth texture of CP soap.

Technically, hot process soap can be used soon after making (ensuring it has been tested and saponification is actually complete), however many hot process soap recipes have higher water amounts and other liquids added during the cook, so a 4-6 week cure is still recommended.
See also: saponification, soap volcano, curing soap

Hygroscopic
A substance is hygroscopic when it attracts and absorbs water from the atmosphere. Sodium hydroxide and potassium hydroxide are both highly hygroscopic and need to be stored in properly sealed containers in a dry place at all times. Particular attention is required to storage if you live in a high humidity area. Note that soap itself is a type of sodium salt which itself is hygroscopic, therefore it will dry/cure less rapidly and may even feel moist on the surface in high humidity environments.

Lye
A term commonly used for the water and sodium or potassium hydroxide solution used to mix with oils to make soap. Can also refer to the sodium or potassium hydroxide in granular/flake form before being dissolved in water.

Lye calculator / soap calculator
Most often lye calculators are web-based tools designed to assist soap makers to calculate their own bar or liquid soap recipes without having to use saponification (SAP) value tables and manual calculations. Note that most soap calculators will provide slightly different lye amounts due to the different saponification values used for each oil in the calculator (most SAP values are averages, the actual values vary between oils from different regions, seasons and variety of plants/animal sources). See my soap calculators page for suggested soap/lye calculators.

Lye concentration
A term that refers to the concentration of sodium hydroxide (bar soap) or potassium hydroxide (liquid soap) in a lye water solution for a given soap recipe. ***This term does not refer to the concentration of lye in the overall soap recipe, it only refers to the concentration of the lye in relation to the water amount within the lye-water solution. For example, in a 40% lye concentration lye-water solution, 40% of the weight of the solution will be the sodium or potassium hydroxide, and 60% will be water. In a 50% lye concentration lye-water solution, there will be equal weights of water and sodium or potassium hydroxide (depending on what type of soap is being made). This video explains this concept and the three ways water amounts can be calculated in soap recipes in greater depth. It can be confusing!
See also: water as percentage of oils, water to lye ratio, water discount

Lye discount
This term is actually what most of us mean when we refer to the ‘superfat’ amount in our soap recipes. When we tell a soap calculator that we want a 5% superfat (for example), the calculator does not add extra oil into the recipe calculation, it reduces the lye amount in the recipe to give the soap the 5% oil excess, hence the accurate term ‘lye discount’ compared to what we often think of as a ‘superfat’. A true superfat would be when we add extra oil to our soap recipe, which I don’t recommend. This video explains all the details of lye discounting and superfatting in depth.
See also: superfat

Lye solution
The mixture of water (can be other liquids) and sodium hydroxide or potassium hydroxide that is added to and blended with oils in correctly calculated amounts to make soap.

MSDS
Short for ‘material safety data sheet’. Every soap maker should have read and be familiar with the MSDS for their sodium or potassium hydroxide products they use in their soap making. Be aware that these products differ between manufacturers and regions around the world. It is important to know exactly what product you are using when making soap and understand the safety requirements involved. Please see my soap making safety essentials video for more information.

OO
Short for ‘olive oil’

pH
A term in chemistry referring to the scale of acidity or alkalinity of any given substance, expressed as a number between 0-14, where acidic ingredients have a low pH (0-7) and alkaline ingredients have a high pH (7-14). A pH reading of 7 indicates neutral.

In the context of soap making, pH is important. Soap makers understand that:

fatty acids (oils, fats, butters and waxes) used in soap making are mildly acidic.
sodium hydroxide and potassium hydroxide lye solutions are highly alkaline/base (and are extremely corrosive - proper preparation and care needs to be taken when handling them).
Fully saponified soap is a naturally alkaline product ranging between 8-10 on the pH scale.
Soap needs to be tested for correct pH (and therefore safety) before using.
(This video details my method for testing pH in handmade soap)
See also: zap test

Potassium hydroxide
Has the chemical formula KOH and is also known as ‘caustic potash’. Potassium hydroxide is used to make lye solutions for liquid soaps or soft/paste soaps. Potassium hydroxide can also be used in combination with sodium hydroxide to make ‘dual lye’ soaps.

Saponification
The name of the chemical reaction which takes place in soap making when fatty acids (oils and fats) are combined and emulsified with a strong alkaline lye solution to transform the mixture into soap. Once these two parts are emulsified beyond the point of separation, saponification commences and is completed when the soap sets into a solid or semi-solid homogeneous mass and reduces to a pH of 8-10.

Saponification value / SV or ‘SAP’ value
Refers to the number of milligrams of potassium hydroxide (KOH) required to completely saponify one gram of a particular fat. In the context of soap making, ‘SAP value’ charts with average saponification values for different oils and fats used in soap making are used to calculate soap recipes manually or are used in the design of online soap calculator tools (such as these) which are used commonly by hobby and professional soap makers to easily calculate soap recipes.

Sequestering (liquid soap)
The process in which a new batch of liquid soap is left to stand for 1-2 weeks to clarify the solution and allow any sediments to fall to the bottom of the container. The clarified liquid soap can then be poured from the top into a new container.

Silicone rash
The appearance of small bubbles or uneven, pockmarked surface on soap that has been poured into silicone cavity moulds and then warmed/processed in the oven (see ‘CPOP’) to force gel phase. This is a great article detailing some interesting experiments with CPOP and avoiding silicone rash (and alien brains). I have yet to succeed in avoiding silicone rash with my CPOP’d silicone moulded soap, but I haven’t given up yet!
See also: CPOP, gel phase, alien brains

Soap on a stick (seizing)
An unfortunate experience when the soap batter undergoes an extremely rapid saponification reaction and the soap becomes hard before the soap maker can pour the soap into the mould. Most often caused by untested fragrance oils or in combination with high temperatures and/or other ingredients that accelerate trace.
See also: accelerate trace

Soda ash
The completely harmless but undesirable appearance of a thin, powdery white film on finished bars of soap. Soda ash is much more common in high-water soap recipes and soaps that have been left in the open air to set, compared to being covered and wrapped or insulated. Keeping soap warm as it saponifies seems to help prevent soda ash, but the biggest factor in my experience is the amount of water in the soap recipe. Keep your water amount at a moderate level and you shouldn’t have any issues with ashy soap.
See also: water discount

Sodium hydroxide
Has the chemical formula NaOH and is also known as ‘caustic soda’. Sodium hydroxide is used to make lye solutions for liquid soaps or soft/paste soaps. Can be used in combination with potassium hydroxide to make ‘dual lye’ soaps. A very highly alkaline and corrosive product. Please refer to MSDS and this video for more information.

Superfat
Fully explained in this video, this term relates to the practice of calculating a soap recipe with either an excess oil amount or a reduced lye amount to ensure that there are some excess, unsaponified oils/fats in the finished soap product. Superfatting or lye discounting is done for two main reasons:

To provide a safety buffer of unsaponified oils/fats in the recipe due to the averaging of saponification values used in soap calculators that may not be accurate for all oils due to regional, seasonal and varietal differences.
To add some extra conditioning quality to the soap via the excess unsaponified oils in the mixture.
See also: lye discount

Stick blender
Another term for ‘immersion blender’ or ‘hand blender’. A handheld blender commonly used for soap making due the convenience of being able to immerse the head of the blender into and under the surface of the soap batter, reducing the chance of splashing.

Soap volcano
The potentially hazardous, sometimes scary and sometimes fun (if you are ready) experience of a liquid or bar soap batter overheating and bubbling/frothing up in the cooking pot or out of the mould (not so fun), in the case of bar soap. Soap volcanoes are relatively common in liquid soap making and hot process soap making due to acceleration of the saponification reaction through the cooking/heating process. This is why HP and liquid soap makers must supervise their soap pot at all times, use a large enough pot, and be prepared to stir down their soap quickly when it puffs up. The likelihood of soap volcanoes depends greatly on temperature and the oils and fats used in the soap recipe and is fairly unlikely in cold process soap making except where fast saponifying oils (eg. coconut) are used in large amounts, excess sugars are added and/or the soap batter is too warm or over-insulated.
See also: accelerating trace, saponification

Trace
A common term in soap making referring to the point when a soap batter starts to thicken and becomes pudding-like, which is demonstrated by the appearance of a ‘trace’ or trail of soap that is visible when some of the soap batter is lifted out of the pot and drizzled back over itself.

Water discount
My most disliked term in soap making due to its inconsistent use, varied meanings and the unwillingness of many soap makers to clarify exactly what they are referring to when they use it. Generally speaking, to ‘discount’ water in a soap recipe is to reduce the water amount, which makes perfect sense. However, often when this term is used it is expressed as a percentage discount amount, for example, “I used a 20% water discount”, which actually most often refers to the amount of water the person is putting in their soap recipe in relation to the oil amount in the recipe, and not referring to a discount at all!

The term originated (I think) from its related term ‘full water soap’, which for most people means a soap recipe that is calculated with the default water amount provided in most soap calculators, 38% water 0as a percentage of the total oil amount. The problem with this is that there are numerous ways to calculate the water amount in a soap recipe, and the ‘water as a percentage of oils’ method is only one of them, so when a person says “I’m using 20% water” or “20% water discount”, not everyone will be speaking the same soap language and it can easily be misinterpreted!

I made a video all about all of this here. It’s quite technical (it needs to be), and I do use my whiteboard, but it’s well worth a look if you have any doubt at all about the three main methods for calculating water in soap recipes.

> If this is all really new to you, you might want to check out more of my soap techy videos here
See also: water to lye ratio, water as percentage of oils, lye concentration.

Water to lye ratio
A method for calculating the water (or other liquid) in a soap recipe where the water amount is expressed in terms of its ratio with the sodium or potassium hydroxide (lye) amount in the recipe.

For example, a 2:1 water to lye ratio recipe, where the sodium hydroxide amount (for example) is 50g, would have 2 parts of water for every 1 part of sodium hydroxide, which equates to 100g of water and 50g sodium hydroxide. A 1.5:1 water to lye ratio for the same soap recipe would have 75g (1.5 times the sodium hydroxide amount) of water and 50g of sodium hydroxide.

The sodium or potassium hydroxide amount in the recipe does not change, that is determined by the soap calculator on the basis of the amount and types of oils you enter.

Water as percentage of oils
Another method for calculating the water (or other liquid) amount in a soap recipe where the water amount is calculated and expressed as a percentage of the total oil amount in the soap recipe.

For example, if the soap maker using this method calculates a recipe with 25% water (as percentage of oils) and the total oil/fat amount for the recipe is 1000g, then the water amount will be 25% of 1000g = 250g. Note that you do not need to make these calculations yourself (a soap calculator does that for you), but you do need to know what method of water calculation you are using because there are other methods that also refer to percentage amounts, that if confused can lead to miss calculation of recipes.

If you are not sure, please refer also to ‘lye concentration’ and ‘water to lye ratio’ to help clarify your understanding. There is no one correct way to calculate water amounts for soap recipes, most soap makers choose the method that they like the best and stick to that. You just need to know what method you are using and confirm that you are understanding and using it correctly.

This video explains the three methods and their differences.
See also: water discount

Zap test/tongue test
A valid alternative method for testing the relative neutrality (not pH neutrality, soap is always alkaline at pH 8-10) of a finished soap batch where pH testing equipment is not available. The tongue test or ‘zap test’ as it is commonly known is done by wetting a piece of soap, rubbing the wet soap with a wet finger and then touching your soapy finger to your tongue. If there is no ‘zappy’ feeling, tingling or stinging whatsoever, and the soap just tastes like, well, soap… it is considered to have passed the zap test, is ‘tongue neutral’ and is therefore safe to use (Dunn, 2010).
(See my favourite book section with a listing for Dunn’s Scientific Soap Making).
See also: saponification and pH.

Reference:
Dunn, Kevin. 2010. Scientific Soapmaking: The Chemistry of the Cold Process. Clavicula Press.