Why were ashes and animal fats used by early soapmakers?

Early soapmakers used ashes and animal fats because these materials provided the essential chemical components required for saponification, the process of creating soap.1

• Ashes: Wood or plant ashes contain alkali carbonates, such as potassium carbonate. When these ashes are dispersed in water, they create an alkaline liquor known as lye, which is necessary to react with fats.123
• Animal Fats: Fats serve as the source of fatty acids. Early soapmakers boiled these fats with the alkaline lye solution, causing a chemical splitting of the neutral fat. The resulting fatty acids then reacted with the alkali carbonates from the ash to form soap.1

By combining these two readily available natural resources, early civilizations were able to produce a functional cleansing agent. This method remained the standard for soap production until the end of the Middle Ages, when the introduction of slaked lime allowed for more efficient causticization of the alkali carbonates.14