does this experiment tell you? anything? >> nothing much. >> reporter: food scientist dr. john lucie says it's just dehydrated food. >> if you took a steak home and cooked it and forgot about it, you'd get something similar. >> reporter: how about the bun? regular bread gets moldy. >> yeah, but the burger buns are different because they're made to be lower moisture content because they have to be tougher. >> reporter: he has no connection to mcdonald's, but the company made the same argument. if food is/or becomes dry enough, it won't grow mold or bacteria. >> a happy meal, fountain of youth. >> reporter: the funny thing is how many people keep old fast food. >> this is going on four years old. and it's aging better than me. >> reporter: one guy has a burger museum dating back more than 20 years. >> the world's first immortal hamburger. >> reporter: morgan spurloch did a similar experiment when he made "super size me."