"Industrially-produced lard, including much of the lard sold in
supermarkets, is rendered from a mixture of high and low quality fat
sources from throughout the pig. It is typically hydrogenated (which
produces trans fats as a by-product), and often treated with bleaching
and deodorizing agents, emulsifiers, and antioxidants, such as BHT.
Such treatment makes lard shelf stable."
SOURCE: http://en.wikipedia.org/wiki/Lard