My mother told me about this today to make our homes more angelic. How Islam preserves Semitic culture.
In Yemen, the Jewish custom of old was to bleach wheaten flour on Passover, in order to produce a clean and white unleavened bread. This was done by spreading whole wheat kernels upon a floor, and then spreading stratified layers of African rue (Peganum harmala) leaves upon the wheat kernels; a layer of wheat followed by a layer of Wild rue, which process was repeated until all wheat had been covered over with the astringent leaves of this plant.
“The beta-carboline alkaloids present in medicinal plants, such as Peganum harmala and Eurycoma longifolia, have recently drawn attention due to their antitumor activities. Further mechanistic studies indicate that beta-carboline derivatives inhibit DNAtopoisomerases and interfere with DNA synthesis."
https://en.wikipedia.org/wiki/Peganum_harmala