"Part of what we're looking for is total anonymity," said Chief Operating Officer Michael Roberts in an interview following the company's annual shareholders meeting last week.
Two days after the Oak Brook-based fast-food giant's September 2002 announcement of efforts to switch to a cooking oil with less trans fat, its customer service line was flooded with calls from people who complained that the fries tasted bad.
To avoid another round of placebo-effect feedback, McDonald's executives aren't disclosing how many restaurants are using the new oil, where those restaurants are located or exactly when the testing moved out of the lab and into the field.
For McDonald's, the risk of tinkering with its legendary french fry formula is huge.
And so is the risk of doing nothing, given growing concerns about the health risks of trans fat.
It's clearly one of their top signature products," said Dennis Lombardi, executive vice-president of WD Partners, a Columbus, Ohio-based restaurant design and development firm.
"Changing the formulation of a signature product for a major brand is not something to be done lightly."
For instance, when rival Burger King added a starch coating to its fries in the mid-1990s in an effort to improve the taste, sales of fries plunged.
In the fast-food arena, burger prices tend to be highly competitive, with the beefy margins coming from fries and soft drinks.
But if McDonald's were to do nothing to reduce trans fat in its fries, it would risk continued criticism from public health and nutrition experts, given trans fat's link to cardiovascular disease and possibly cancer.
"I can appreciate the Herculean feat McDonald's faces in reducing trans fat in its fries while still preserving the great taste," said Dave Grotto, director of nutrition at Block Medical Center in Evanston and a spokesman for the American Dietetic Assn.