McDonald's still won't reveal the recipe for its secret sauce, but it will show you how that Big Mac patty gets made. Keith Srakocic/AP hide caption toggle caption Keith Srakocic/AP The Salt What's Really In A Big Mac? McDonald's Says It's Ready To Tell All October 14, 2014 Pink slime? Eyeballs? Rumors about what goes into McD's food have dogged it for years. As U.S. sales falter, the firm's new ad campaign aims to tackle those concerns by inviting consumers' questions.