About 50 years ago, modern machinery, chemical engineering and abundant energy made it possible to speed up the soapmaking process and utilise low quality oils.
In order to make soap in this way, it is necessary to split the glycerol from the fatty acids.
Commercially this is done by treating the oil with hot water in a hydrolyser and then distilling off the fatty acids released by the process, leaving the glycerol behind.
The distilled acids are then treated with alkali (sodium or potassium hydroxide), mixed and blended and then builders and other ingredients (including preservatives, artificial fragrances and colours) added; the mixture is then cooled, compressed and dried.
With the glycerol removed the soapmaking process can be sped up and modern factories now produce at rates of 50 tonnes per hour.
The glycerol is converted to glycerin, which is then sold in moisturising and hair preparations.
The advantages of modern factory soapmaking are:
- high volume, low cost product;
- low cost feedstock (mostly animal fats - an abattoir waste problem);
The disadvantages are:
- low quality product (no glycerin);
- energy and machinery intensive;
- nutrients destroyed by heat and pressure;
- process requires the use of preservatives and fragrances to cover the decay of the broken down oils;
- significant environmental impact caused by the manufacture and use.