There could be a lot of factors. Firstly, are you 100% sure that it's mimosa hostilis? It has long, white blooms. Not all mimosa trees have significant amounts of spice.
2nd, it could be the drying method. You want to dry the roots in a warm, dark area. If you dry them in direct sunlight it will definitely have adverse effects on yield.
It could be the roots themselves. I've heard that the younger, horizontal roots are better to harvest because of less impact on the plant. I haven't done enough testing to know for sure though.
Convert a melodic element into a rhythmic element...