McDonald's, admitting that it overcooks some burgers, is planning to add salt and pepper to the ingredients, rather than relying on tomato ketchup to give them their distinctive taste.

For the "Arch Deluxe", its new burger aimed at adults, McDonald's will even break with its long tradition of slapping the lettuce and tomato along with the burger into a microwave, a practice that makes Big Macs taste of warm, wilted lettuce. At rivals, the trimmings are added by customers.

These changes follow criticism from franchisees - the people who pay McDonald's for the privilege of being allowed to sell its burgers. The Deluxe line, introduced to great fanfare earlier this year, has drawn unflattering reviews from analysts, who have called them "magnificently mediocre".

The company, which has 18,300 outlets worldwide, has sent a memo entitled "Maximising Taste at McDonald's," to franchisees. It contained detailed cooking instructions.

The memo's author, executive vice-president Thomas Glasgow, disseminated the cooking tips after McDonald's chairman Michael Quinlan spoke of solving "product taste challenges".

The memo is an implicit acknowledgment that the world's first name in fast food still has a few things to learn in the kitchen. Mr Glasgow, sounding as much like Elizabeth David as a top executive, writes: "Overcooking is the No.1 enemy of beef flavour."

He advises that the meat should be cooked "above but as close to 155 degrees as possible," a temperature health experts consider approriate to kill any bacteria.

As McDonald's expands into Tahiti, Belarus and India, sales in the US have been flat or down for most of the year at the 12,000 US outlets.