The brand's top executive admitted his nerves were aflutter despite the tight security he lined up for the operation.
"I don't want to be the president who loses the recipe," KFC President Roger Eaton said. "Imagine how terrifying that would be."
So important is the 68-year-old concoction that coats the chain's Original Recipe chicken that only two company executives at any time have access to it. The company refuses to release their name or title, and it uses multiple suppliers who produce and blend the ingredients but know only a part of the entire contents.
Louisville-based KFC, part of the fast-food company Yum Brands Inc., hired off-duty police officers and private security guards to whisk the document away to an undisclosed location in an armored car. The recipe will be slid into a briefcase and handcuffed to security expert Bo Dietl for the ride.
"There's no way anybody could get this recipe," said Dietl, a former New York City police detective. His security firm is also handling the security improvements for the recipe at headquarters, but he wouldn't say what changes they're making.
For more than 20 years, the recipe has been tucked away in a filing cabinet equipped with two combination locks in company headquarters. To reach the cabinet, the keepers of the recipe would first open up a vault and unlock three locks on a door that stood in front of the cabinet.
Vials of the herbs and spices are also stored in the secret filing cabinet.
"The smell is overwhelming when you open it," said one of two keepers of the recipe in an interview at company headquarters.
The biggest prize, though, is a single sheet of notebook paper, yellowed by age, that lays out the entire formula - including exact amounts for each ingredient - written in pencil and signed by Sanders.
Others have tried to replicate the recipe, and occasionally someone claims to have found a copy of Sanders' creation. The executive said none have come close, adding the actual recipe would include some surprises.
Sanders developed the formula in 1940 at his tiny restaurant in southeastern Kentucky and used it to launch the KFC chain in the early 1950s.
Sanders died in 1980, but his likeness is still central to KFC's marketing.
"The recipe to him, in later years, was everything he stood for," said Shirley Topmiller, his personal secretary for about 12 years.
Larry Miller, a restaurant analyst with RBC Capital Markets, said the recipe's value is "almost an immeasurable thing. It's part of that important brand image that helps differentiate the KFC product."
KFC had a total of 14,892 locations worldwide at the end of 2007. The chain has had strong sales overseas, especially in its fast-growing China market, but has struggled in the U.S. amid a more health-conscious public. KFC posted U.S. sales of $5.3 billion at company-owned and franchised stores in 2007.