Despite its name, it is primarily composed of pork shoulder meat, according to McDonalds.[1] However, according to Chicago Magazine, the patty is composed of restructured meat products such as tripe, heart, and stomach and blended with salt and water to extract salt-soluble proteins, which act as a "glue" that helps bind the reshaped meat together.[2]
McDonald's sold 30 million made with over 7 million pounds of pork in 2007.[1]
The Chappelle's Show sketch "Calvin Gets a Job at WacArnold's" (a parody of McDonald's) references the McRib. Upon realizing that his girlfriend has been cheating on him, Calvin, a WacArnold's employee, yells out "And guess what, the rib sandwich is coming back on Tuesday! Guess who ain't getting one!?"[16]
http://en.wikipedia.org/wiki/McRib