Castor Oil: Hulled Castor Beans Pressed Cold, then Steamed and Filtered

Castor beans are about half oil. For the best oil, the trade hulled the beans and pressed the kernels without solvent, then steamed the crude oil so its albumin curdled and could be filtered out (Thorpe, 1912). The beans and the press-cake are poisonous (ricin): the oil is pressed out, and the poison stays in the cake. The picture: castor beans (Wikimedia Commons, public domain).