Complex sentence: Second, the shea nut is shelled; historically, shelling is done by mortar and pestle or by crushing the shell with stones; however, the Universal Nut Sheller is an appropriate technology that reduces a significant amount of labor involved in shelling shea.
Split into simpler sentences: Second, the shea nut is shelled; historically, shelling is done by mortar and pestle or by crushing the shell with stones. In some instances, the Universal Nut Sheller may be an appropriate technology that sometimes reduces a significant amount of labor involved in shelling shea.