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.