Soap Nuts are a berry that grows on a tree and naturally contains a cleaning agent called saponin that acts as a detergent (though often referred to as a “soap” – it’s not a true soap which is made with lye and oils). The cleaning agent can be used as an excellent multipurpose cleaner, and indeed has been used as one for centuries around the world, particularly in areas of Asia and by Native Americans.
There are many different kinds of soap nuts that grow all over the world, but usually what you see for sale come from the Sapindus mukorossi tree in the Himalayas and will be the focus of this article.
The Sapindus mukorossi tree is a deciduous tree found wild in north India, Nepal and China. This tree belongs to the plant family Sapindaceae. Other plants that share this family are the maple, horse chestnut, and lychee. The common names for the plant are “soapberry tree” or “soap nut tree” though the parts of the tree that is used for washing are a fruit and not a nut. The name “soap nut” is a misnomer, though it’s easy to see why if you take a look at the berries themselves. The fruit, when dried, turns into a hard brown shell that resembles an acorn. The fruit/nut distinction is important because many people have nut allergies and these, not being actual nuts, won’t aggravate those allergies and can be safely used by people with these sensitivities.
The Sapindus mukorossi fruit is the largest of the soapberry trees which makes them ideal to use for washing laundry – they contain more saponin and last longer through multiple laundry loads.
Nothing is added to the berries to make them soapy – the cleaning agent/detergent is made by the tree for various reasons which are still being studied. For the most part, science agrees that saponin tastes bad to insects (it tastes like soap!) and may have other functions within the plant as part of its immune system. Saponin is a well-studied compound and has been utilized in many different industries, but is well recognized for its ability to act as a natural surfactant. When you see detergents that list “natural surfactants” as an ingredient, they are likely referring to saponin, either from soap berries or other plants that also contain saponin.
The fruit is a drupe – having a fleshy outer part and a “stone” or pit seed in center. Other examples of drupes include peaches, coffee beans, coconuts and cherries.
This tree grows best in poor uncultivated deep clay loam soil and thrives in areas that experience 60 to 80 in of annual rainfall. The tree can reach a height of 90 ft and a girth of 9-16 ft. The trees also produce fruit for 70-90 years (different sources vary on the exact number of years the tree lives for). The wood is hard, close-grained and light yellow in color.
The tree flowers during summer. The flowers are small and greenish white and the fruit appears in July-August and ripens by November-December. The soapberries are round and as discussed before, about the size of acorns. They start out green and then turn yellow and then brown. The seed is enclosed in a black, smooth and hard round endocarp. The endocarp, or outside fleshy part of the fruit is what contains the saponin and is what is used for cleaning, not the seed itself.
The soapberry harvest goes from December-February.
To use these for laundry, the empty shells are placed in a cotton bag (just so they aren’t lost) and they are put in the washing machine along with clothes, linens or whatever else is being washed. When they are immersed water, they will release the saponin. Most people don’t see any bubbles – saponin doesn’t make great bubbles but it still cleans. The saponin is also extracted to be used in liquid detergents and other cleaning products. If you’d like to try these for yourself, check out our web store where you can find the berries, liquid detergent, and other cleaners.