How are soapberries used to make a soapy lather?

Soapberries, which belong to the genus Sapindus within the Sapindaceae family, produce a soapy lather due to their high concentration of saponin. The fruit of these trees and shrubs can contain as much as 37 percent of this substance.1

When the fruit is mixed with water, the saponin acts as a natural detergent or surface-active agent. Saponins are characterized by their ability to produce a soapy lather, which functions by reducing the surface tension of water and allowing it to emulsify and remove dirt. In various tropical regions, this natural property allows the fruit to be used directly as a soap substitute.1234