Can soap nuts develop mold or fungus?
Of course – if left sitting in water or stored wet. All botanicals will. Even though soap nuts have natural anti-fungal and anti-microbial properties, remember that a soap nut is a still an unpreserved dried fruit. Simply treat it as such, and use plain old-fashioned common sense. Just because a lemon – which is totally loaded with citric acid – does not mean it won’t ever rot.