Plenty of fizz and sparkle behind the secret recipes

Coca-Cola keeps the recipe for its 127-year-old soda inside an imposing steel vault that is bathed in red security lights. Several cameras monitor the area to make sure the fizzy formula stays a secret.

But in one of the many signs that the surveillance is as much about theatre as reality, the images that pop up on video screens are of smiling tourists waving at themselves.

"It's a little bit for show," concedes a guard at the World of Coca-Cola museum in Atlanta, where the vault is revealed at the end of an exhibit in a puff of smoke.

The ability to push a quaint narrative about a product's origins and fuel a sense of nostalgia can help drive billions of dollars in sales. That's invaluable at a time when food makers face greater competition from smaller players and cheaper supermarket store brands that appeal to cash-strapped consumers.

It's why companies such as Coca-Cola and Twinkies' owner Hostess play up the notion that their recipes are sacred, unchanging documents that need to be closely guarded. As it turns out, some recipes have changed over time, while others may not have. Either way, they all stick to the same script that their formulas have remained the same.

John Ruff, who formerly headed research and development at Kraft Foods, said companies often recalibrate ingredients for various reasons, including new regulations, fluctuations in commodity costs and other issues that impact mass food production.

"It's almost this mythological thing, the secret formula," said Ruff, now president of the Institute of Food Technologists, which studies the science of food. "I would be amazed if formulas [for big brands] haven't changed."