Many items naturally exist as organic wholes, but people have figured out how to grind them up and break them down to create new and wonderful things. By grinding up wheat and other grains, we make flour, which in turn can be used to bake bread, cake, and much more. Cayenne pepper is made by grinding up chili peppers. By grinding certain plants and herbs, medicines are made. Since grinding is a creative activity, it is included in the melakhot prohibited on Shabbat.
The prohibition of Grinding applies to natural items (such as plants, fruits, and metals), but does not apply to foods already ground up during processing. Therefore, bread, matza, cookies, chocolate, or hardened sugar may be crumbled, and pills may be crushed.