What you should know as a newbie in soap making

Soap is an important commodity in our daily lives. Therefore, it is crucial to know some key terms that are used and how to make your soap if you’re in position to do so or if you wish to start business in soap making. Everybody knows soap but does everybody know its definition? According to Oxford Advanced Learner’s Dictionary defines soap as a substance that you use with water for washing your body  or objects. Soap consists of two ends, the hydrophilic end and hydrophobic end. During washing hydrophobic end interacts with dirt while hydrophobic end interacts with water and due to this hydrophobic components form miscelles which pull away from water. When this is rinsed with water, the dirt is carried away by water.

 Oils or fats used in soap making are divided into three classes: mineral oils, essential oils and fixed oils. Since majority of the oils/fats in soap making fall in class of fixed oils, this article discusses fixed oils.

 Fixed oils 
 These oils and fats in this class are further divided according to their physical properties as:

(i) Nut oils: These are characterized by a large proportion of fatty acids with low molecular weight, for example, lauric acid, palm kernel oil, and coconut oil.They have pros of  easily saponifying with strong alkali but require large amount of brine (sodium chloride) for graining.

(ii) Hard fats: This class contains a good amount of palmitic acid and stearic acid, for instance, palm oil, animal tallow, and hydrogenated oils. These oils produce slow lathering but lather produced is more stable for long duration of time than of the previous class. They always saponified with weak alkali and in the advance stages with stronger alkali.

(iii) Soft oils: This class  majorly composed of oils or fats with unsaturated acids like oleic acid, linoleic acid, groundnut oils, castor oil, cotton oil, fish oil and olive oil. These oils are blended with other oils since they produce soap of poor quality. But they lather freely and have excellent detergent properties.

 Terms used in soap making 
The following terms are frequently used in soap making.

 Saponification value: It determines the quantity of caustic soda or potash required to neutralize(saponify) a given amount of fat or oil in making soap or it is the amount of caustic soda (in milligrams) required to neutralize 1 gram of oil or fat. It is often  expressed in terms of caustic potash. Hence, the value given must be multiplied by 0.7 to get its value in terms of caustic soda. 0.7 is obtained by divided molecular weight of caustic soda (NaOH) by molecular weight of caustic potash (KOH), for example:

 Relative molecular weight of caustic potash (KOH), K = 39, O = 16, H=1

{39 + 16+1} = 56 grams

 Relative molecular weight of caustic soda (NaOH), Na= 23, O = 16, H= 1

{23 + 16 +1} = 40 grams

 Now, dividing 40 by 56 gives (40/56) = 0.7

 Example
 How much quantity of caustic soda a soap-maker who has 4kg of palm oil use? When saponification value is 202.

 Solution 
 To calculate this, the saponification value will be multiplied by 0.7 and the weight of the oil . It is given as follow:

Caustic soda (NaOH) required = 0.7 X saponification value/weight of oil in grams

{0.7 X 202  X 4000/1000} = 565.6 grams.

If you use online calculator then you will find a slight difference between the calculated and Online Lye Calculator  values. Hence, one can determine amount of lye to be used without using Online Lye Calculator .

 Iodine number: It is the number of centigrams of iodine absorbed by one gram of oil or fat. This number indicates the number of unsaturated acids in the sample. The higher the number the greater the presence of these acids. The higher iodine number value produce soft soaps.

 INS factor: This is expressed as the difference between the iodine number and saponification value of the oil/fat. It is used to predict the quality of the soap to be obtained from the blend of oils or fats. INS factor number ranges from 15 to 250.

 When INS factor increases the following occur:

(i)The oil varies from oil to solid and produces harder soap.

(ii)The detergent and lathering properties and also the solubility of the soap decreases (but increases in nut oils) with improved color and capability to hold more filling agents.

 (iii)The soap or oil diminishes in its tendency to go rancid on ageing. 

Application of INS factor 
A soap-maker wants to make a blend of beef tallow, coconut oil and cotton seed oil in such away that the blend has INS factor of 150 which corresponds to INS factor of  beef tallow and lies within the INS factor range of soap oils. It should contain 50% of beef tallow. How much(in percentage) of each constituent in the blend should the soap-maker use?

 Solution 
 In this problem, one need to determine the percentage of cotton seed oil (lets say b) and coconut oil (50-b) which must be added to the beef tallow to form the blend. Given that, INS factor of beef tallow  = 150, coconut oil = 250, cotton seed oil = 85.

Therefore;

 50/100 X (INS factor of beef tallow) + (50-b)/100 X (INS factor of coconut oil) + b/100 X (INS factor of cotton-seed oil) = 150.

 It is known that the blend should constitute 50% of beef tallow, and then the 50% should be composed of coconut oil and cotton seed oil. In the above statement, the percentage of cotton seed oil is represented by “b” hence the percentage of coconut oil will be (50-b). The blend should be equal to INS factor of beef tallow  ‘150’.

 {50/100 X 150} + {(50-b)/100 X 250} + {b/100 X 85} = 150

75 + 125 -2.5b + 0.85b = 150 1.65b = -50

b= -50/-1.65

b = 30.3%

 The blend will compose of 50%  beef tallow, 19.7% of coconut oil and 30.3% cotton seed oil. This can be done to any preferred oils of your blend. To calculate this you should know the INS factor of oils in the question.

 Note:  oils or fats  blend with INS factor range  between 130 and  160 is not suitable for making soaps. The lathering and solubility of a soap depends on the INS factor of oil blend.